Thèses : « Multiferroic Oxides - Structural Properties »

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Vaghefi, Seyedeh Pegah Mirzadeh. « Structural and physical properties studies on multiferroic oxide films and heterostructures ». Doctoral thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/18502.

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Doutoramento em Engenharia Física
O presente trabalho de doutoramento é um estudo de propriedades físicas e aspectos estruturais de filmes de óxidos e heteroestruturas multiferróicas, englobando técnicas de caracterização do nível macroscópico ao microscópico. O objectivo principal é a compreensão de novas heteroestruturas epitaxiais multifuncionais e as suas interfaces para junções de túnel magnetoelétricas e filtros de spin. Os principais materiais em estudo foram manganitas à base de La dopadas com iões divalentes (ba, Sr), apresentando efeito magnetoelétrico, sendo preparadas em diferentes substratos e diferentes técnicas de crescimento, optimizadas para epitaxia e qualidade de interface. O estudo combinado de propriedades eléctricas e magnéticas permitiu estabelecer as condições necessárias para a aplicação dos materiais multiferróicos em estudo, por técnicas experimentais apresentadas neste trabalho. O trabalho consistiu no estudo sistemático de microestrutura de filmes finos de La0:7Sr0:3MnO3 em substratos de SrTiO3, preparados por pulsed laser deposition, o filme fino de La0:9Ba0:1MnO3 e a heteroestrutura La0:9Ba0:1MnO3/BaTiO3/La0:9Ba0:1MnO3 em substrato de Al2O3, e filme fino de La0:9Ba0:1MnO3, BaTiO3 e heteroestrutura de La0:9Ba0:1MnO3/BaTiO3/La0:9Ba0:1MnO3 em substrato de Si, preparado por RF magnetron sputtering. A caracterização estrutural das amostras foi feita principalmente por difracção de raio-X (XRD) convencional e de alta resolução e Microscopia de Transmissão de Alta Resolução (HRTEM). A composição química foi analisada por Electron Dispersion Spectroscopy (EDS), Rutherford backscattering spectroscopy (RBS) e energy filtered transmission electron microscopy (EFTEM). As medidas de magnetização forram realizada com a um magnetómetro superconducting quantum interference device (SQUID). A análise da topografia e efeitos locais foi realizada por microscopia de varimento de ponta usando microscopia da Força Atómica (AFM) e de resposta piezoeléctronica (PFM). Os resultados mostram claramente uma evolução da microestrutura dos filmes finos de La0:7Sr0:3MnO3, á medida que aumenta a sua espessura, passando de uma estrutura policristalina no filme mais fino (13.5 nm) a colunar inclinado (45 nm e 200 nm), a uma estrutura ramificada no filme mais espesso (320 nm). A alteração na estrutura do filme é devida à tensão pelo substrato e deformação da estrutura nas etapas iniciais de crescimento, onde se detectaram fronteiras anti-phase e maclas. A evolução da estrutura modificou as propriedades magnéticas dos filmes a baixa temperatura (abaixo da temperatura de transição estrutural do substrato de SrTiO3), mostrando magnetização em excesso e defeito, para espessuras abaixo e acima de 100 nm, respectivamente. Análises STEM-EELS e EFTEM mostraram a diferença em composição elementar dos filmes perto das fronteiras e na interface com o substrato.No âmbito do plano de trabalhos de doutoramento, o segundo substrato consiste em estudar as propriedades físicas e estruturais de filmes finos de La0:9Ba0:1MnO3 e heteroestruturas La0:9Ba0:1MnO3/BaTiO3/La0:9Ba0:1MnO3 em substratos de Al2O3, revelando estruturas altamente orientadas. A razão La/Ba do filme e heteroestrutura é drasticamente diferente do alvo providenciado, La0:7Ba0:3MnO3, como provado por XRD, RBS e transições de fase magnéticas. As propriedades magnéticas e eléctricas das estruturas mostraram uma forte dependência na cristalinidade do filme e da heteroestrutura. A parte final do trabalho é dedicada aos filmes de La0:9Ba0:1MnO3, BaTiO3 e a heteroestrutura de La0:9Ba0:1MnO3/BaTiO3/La0:9Ba0:1MnO3 em substrato de Si, que em comparação com as estruturas em substrato de ALO, provaram o efeito da cristalinidade nas propriedades magnéticas, eléctricas e de magneto-resistência do filme e heteroestrutura. Foi mostrado que um grau superior de cristalinidade leva a uma mais elevada magnetização, reduzindo a resistividade das estruturas. Pela primeira vez, um estudo de deformação de topografia por aplicação de uma tensão dc externa foi feito num filme fino de BaTiO3 em Si, usando uma técnica de poling num microscópio de força piezoresponse. Os resultados mostraram a capacidade de uma modificação controlada da superfície, por aplicação de uma voltagem externa nointervalo 14V < Vapp < 20V. Abaixo destes valores, não se observou alguma deformação na topografia, enquanto acima deste intervalo, a 30V, a superfície foi completamente danificada. A mudança topográfica produzida mostrou estabilidade no tempo, onde após a aplicação de 20V, a área modificada alcançou 83% da altura as-poled ( 9 nm) em 90 minutos, a 7,4 nm. A resposta assimétrica de piezoresponse da área poled foi associada à existência de um campo eléctrico interno na amostra, que foi também provado através de medidas de espectroscopia de switching no filme fino. A heteroestrutura no substrato de Si mostraram o mesmo fenómeno que a mono-camada de BaTiO3, onde o arranjo de heteroestrutura realça o efeito de voltagem aplicada na topografia. Aplicando 10V, a estrutura da superfície foi alterada na heteroestrutura e houve uma modificação visível da camada de BaTiO3, alterando também a topografia da camada superior de La0:9Ba0:1MnO3.
This present PhD work made a study of structural aspects and physical properties of the oxide films and multiferroic heterostructures, encompassing the techniques from macroscopic level to microscopic description. The understanding of novel multifunctional epitaxial heterostructures and their interfaces for magneto-electrically driven tunnel junctions and spin-filters is the central objective. The main materials in study were La based doped manganites with magnetoelectric effect prepared on different substrates and growth conditions, optimized for epitaxy and interface quality. The combined study of electric and magnetic properties allowed us examining the conditions required for application of the studied multiferroic materials and experimental techniques are presented in this work. The work consists of three main substrates, a systematic study of microstructure of La0:7Sr0:3MnO3 thin films on SrTiO3 substrate, prepared by pulsed laser deposition, the La0:9Ba0:1MnO3 thin film and La0:9Ba0:1MnO3/BaTiO3/La0:9Ba0:1MnO3 heterostructure on Al2O3 substrate, and the La0:9Ba0:1MnO3 thin film, BaTiO3 and La0:9Ba0:1MnO3/BaTiO3/La0:9Ba0:1MnO3 heterostructure on Si substrate, prepared by RF magnetron sputtering. Main structural characterization of samples was performed by conventional and high resolution X-Ray Diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM); chemical composition was determined by Electron Dispersion Spectroscopy (EDS), Rutherford Backscattering Spectroscopy (RBS) and Energy Filtered Transmission Electron Microscopy (EFTEM); Magnetization measurements done with a Superconducting Quantum Interface Device (SQUID) magnetometer. Surface probing of topography and local effects was performed, using Atomic Force (AFM) and Piezo-Response (PFM) Microscopy. Results clearly showed that there is an evolution in the microstructure of the La0:7Sr0:3MnO3 thin films, by increasing their thickness, changing from polycrystalline structure in the thinnest film (13.5 nm) to tilted columnar structure(45 nm and 200 nm) and to a branched structure in the thickest film (320 nm). The change in the structure of the film is due to the strain from the substrate and deformation of the structure in the early stages of the growth, where anti-phase boundaries and twinning were detected. The evolution of the structure modified the low temperature (below structural phase transition of SrTiO3 substrate) magnetic properties of the films, showing in-excess and in-defect magnetization, below and above 100 nm thickness, respectively. Also, STEM-EELS and EFTEM analysis showed the difference in the elemental composition of the films near the boundaries and interface with the substrate.In the scope of the PhD work plan, the second substrate consists of studying the structural and physical properties of La0:9Ba0:1MnO3 thin film and La0:9Ba0:1MnO3/BaTiO3/La0:9Ba0:1MnO3 heterostructure on Al2O3 substrate, where they showed highly oriented structure. The La/Ba ratio of the single layer film and heterostructure is drastically different from the target, La0:7Ba0.3MnO3, proven by XRD, RBS, and magnetic phase transitions. The magnetic and electrical properties of the structures showed strong dependence on the crystallinity of the samples. The final part of the work is devoted to the La0:9Ba0:1MnO3 and BaTiO3 thin films and La0:9Ba0:1MnO3/BaTiO3/La0:9Ba0:1MnO3 heterostructure on Si substrate, which in comparison with the structures on Al2O3 substrate, highlights the influence of crystallinity on magnetic, ferro-electrical and magnetoresistance properties of the film and heterostructure. It is shown that higher degree of crystallinity leads to higher magnetization and lowers the resistivity. For the first time, a study of the topography deformation by applying a dcexternal voltage was done on BaTiO3 thin film on Si, using a poling technique in a piezoresponse force microscope. The results show the ability of controlled modification of the surface, by applying an external voltage/electric field in the range of 14V< Vapp<20V. Below this range, no deformation is observed on the topography, and above this interval, at 30V, the surface is completely damaged. The produced topographical change show stabilization in respect to time, where after applying 20V, the modified area reaches its 83% of the as-poled height ( 9nm) in 90 minutes, to 7.4 nm. The asymmetrical response in the piezoresponse of the poled area is related to the existence of an internal built-in electric field in the sample, which is also confirmed by performing switching spectroscopy measurements on the single layer. The heterostructure on the Si substrate shows the same phenomena, as the BTO single layer, where the heterostructure arrangement enhances the applied voltage effect on the topography. With applying 10V, the structure of the surface changes in the heterostructure and a visible modification of BaTiO3 layer, changing also the topography of La0:9Ba0:1MnO3 top layer is observed.

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Rotaru, Andrei. « Novel polar dielectrics with the tetragonal tungsten bronze structure ». Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/4184.

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There is great interest in the development of new polar dielectric ceramics and multiferroic materials with new and improved properties. A family of tetragonal tungsten bronze (TTB) relaxors of composition Ba₆M³⁺Nb₉O₃₀ (M³⁺ = Ga³⁺, Sc³⁺ and In³⁺, and also their solid solutions) were studied in an attempt to understand their dielectric properties to enable design of novel polar TTB materials. A combination of electrical measurements (dielectric and impedance spectroscopy) and powder diffraction (X-ray and neutron) studies as a function of temperature was employed for characterising the dynamic dipole response in these materials. The effect of B-site doping on fundamental dipolar relaxation parameters were investigated by independently fitting the dielectric permittivity to the Vogel-Fulcher (VF) model, and the dielectric loss to Universal Dielectric Response (UDR) and Arrhenius models. These studies showed an increase in the characteristic dipole freezing temperature (T[subscript(f)]) with increase B-cation radius. Crystallographic data indicated a corresponding maximum in tetragonal strain at T[subscript(f)], consistent with the slowing and eventual freezing of dipoles. In addition, the B1 crystallographic site was shown to be most active in terms of the dipolar response. A more in-depth analysis of the relaxor behaviour of these materials revealed that, with the stepwise increase in the ionic radius of the M³⁺ cation on the B-site within the Sc-In solid solution series, the Vogel-Fulcher curves (lnf vs. T[subscript(m)]) are displaced to higher temperatures, while the degree of relaxor behaviour (frequency dependence) increases. Unfortunately, additional features appear in the dielectric spectroscopy data, dramatically affecting the Vogel-Fulcher fitting parameters. A parametric study of the reproducibility of acquisition and analysis of dielectric data was therefore carried out. The applicability of the Vogel-Fulcher expression to fit dielectric permittivity data was investigated, from the simple unrestricted (“free”) fit to a wider range of imposed values for the VF relaxation parameters that fit with high accuracy the experimental data. The reproducibility of the dielectric data and the relaxation parameters obtained by VF fitting were shown to be highly sensitive to the thermal history of samples and also the conditions during dielectric data acquisition (i.e., heating/cooling rate). In contrast, UDR analysis of the dielectric loss data provided far more reproducible results, and to an extent was able to partially deconvolute the additional relaxation processes present in these materials. The exact nature of these additional relaxations is not yet fully understood. It was concluded application of the Vogel-Fulcher model should be undertaken with great care. The UDR model may represent a feasible alternative to the evaluation of fundamental relaxation parameters, and a step forward towards the understanding of the dielectric processes in tetragonal tungsten bronzes.

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Geatches, Rachel M. « Electrical and structural properties of metal oxides ». Thesis, University of Kent, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278079.

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Regoutz, Anna. « Structural and electronic properties of metal oxides ». Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:6f425890-b211-4b35-b438-b8de18f7ae64.

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Metal oxides are of immense technological importance. Their wide variety of structural and electronic characteristics leads to a flexibility unrivalled by other groups of materials. However, there is still much debate about the fundamental properties of some of the most widely used oxides, including TiO₂ and In₂O₃. This work presents high quality, in-depth characterisation of these two oxides in pure and doped form, including soft and hard X-ray photoelectron spectroscopy and X-ray diffraction. Bulk samples as well as thin film samples were prepared analysed. For the preparation of thin films a high quality sol-gel dip-coating method was developed, which resulted in epitaxial films. In more detail the organisation of the thesis is as follows: Chapter 1 provides an introduction to key ideas related to metal oxides and presents the metal oxides investigated in this thesis, In₂O₃, Ga₂O₃, Tl₂O₃, TiO₂, and SnO₂. Chapter 2 presents background information and Chapter 3 gives the practical details of the experimental techniques employed. Chapters 4 presents reciprocal space maps of MBE-grown In₂O₃ thin films and nanorods on YSZ substrates. Chapters 5 and 6 investigate the doping of In₂O₃ bulk samples with gallium and thallium and introduce a range of solid state characterisation techniques. Chapter 7 describes the development of a dip-coating sol-gel method for the growth of thin films of TiO₂ and shows 3D reciprocal space maps of the resulting films. Chapter 8 concerns hard x-ray photoelectron spectroscopy of undoped and Sn-doped TiO₂. Chapter 9 interconnects previous chapters by presenting 2D reciprocal space maps of nano structured epitaxial samples of In₂O₃ grown by the newly developed sol-gel based method. Chapter 10 concludes this thesis with a summary of the results.

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Thrall, Michael. « The magnetic, electric and structural properties of multiferroic BiFeo3 and BiMnO3 ». Thesis, University of Manchester, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492716.

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Bulk BiFe03 samples prepared by the conventional mixed oxide route were investigated. High purity Bi203 and Fe203 powders were weighed according to stoichiometry and milled for 20 hours. The powders were pressed into cylinders (10mm diameter by 6mm thickness) at 100 MPa. The cylinders were heated at a rate of 3 degrees C/min at temperatures of between 700 degrees C and 900Â°C for times between 7.5 minutes and 48 hours. XRD spectra collected from both the as-sintered and 'bulk' (internal) surfaces showed the formation of additional Bi2Fe40, and Bi25Fe04o secondary phases coexisting alongside the main BiFeOs phase.

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Millburn, Julie Elizabeth. « Structural and electronic properties of transition metal oxides ». Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364166.

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Jones, Christopher Wynne. « Structural and electronic properties of mixed metal oxides ». Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235645.

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Abbas, Hussien Ahmed, Fadwaa Fwad Hamad, Atrees Khair Mohamad, Zeinab Mohamad Hanafi et Martin Kilo. « Structural properties of zirconia doped with some oxides ». Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-192913.

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Zirconia powders doped with different amounts of dopants (CeO2, Gd2O3, and CaO) were synthesized by a citrate technique. X-ray diffraction for samples sintered at 1500 °C revealed that the zirconia ceramics were stabilized in the cubic phase above 12 mole % CaO and 10 mole % Gd2O3, while tetragonal zirconia is obtained above 15 mole % CeO2. Relative densities up to 99.5% were obtained. The effect of dopant concentration on the lattice parameter, average crystallite size, microstrain was studied. The cubic lattice parameter increases nearly linearly with increasing the concentration in case of CaO and Gd2O3. The tetragonal lattice parameters at and ct increase nearly linearly with increasing the concentration of CeO2. The average crystallite size was found to be larger than 600 nm for the samples investigated.

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Abbas, Hussien Ahmed, Fadwaa Fwad Hamad, Atrees Khair Mohamad, Zeinab Mohamad Hanafi et Martin Kilo. « Structural properties of zirconia doped with some oxides ». Diffusion fundamentals 8 (2008) 7, S. 1-8, 2008. https://ul.qucosa.de/id/qucosa%3A14153.

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Zirconia powders doped with different amounts of dopants (CeO2, Gd2O3, and CaO) were synthesized by a citrate technique. X-ray diffraction for samples sintered at 1500 °C revealed that the zirconia ceramics were stabilized in the cubic phase above 12 mole % CaO and 10 mole % Gd2O3, while tetragonal zirconia is obtained above 15 mole % CeO2. Relative densities up to 99.5% were obtained. The effect of dopant concentration on the lattice parameter, average crystallite size, microstrain was studied. The cubic lattice parameter increases nearly linearly with increasing the concentration in case of CaO and Gd2O3. The tetragonal lattice parameters at and ct increase nearly linearly with increasing the concentration of CeO2. The average crystallite size was found to be larger than 600 nm for the samples investigated.

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Harrison, W. T. A. « Structural and magnetic properties of some mixed metal oxides ». Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379947.

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Smith, Anna Louise. « Structural and thermodynamic properties of sodium actinide ternary oxides ». Thesis, University of Cambridge, 2015. https://www.repository.cam.ac.uk/handle/1810/263068.

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In the potential event of a clad breach in a Sodium-cooled Fast Reactor (SFR), the sodium metallic coolant could come into contact with the (U,Pu,Np)$O_2$ nuclear fuel. The reaction products are numerous, but there is little knowledge of their structural and thermodynamic properties. Under the oxygen potential conditions of the reactor, pentavalent $Na_3AnO_4$ (An=U,Pu,Np) is expected to form, but its structure was the subject of controversy until now. We showed that $\alpha-Na_3UO_4$ adopts a monoclinic symmetry in space group $\textit{P2/c}$. Neutron diffraction combined with X-ray Absorption Near Edge Structure (XANES) spectroscopy at the U-M$_4$ edge also revealed that this phase could accommodate excess sodium on the uranium site, with subsequent charge compensation of the uranium cation from U(V) to U(VI), which was not previously foreseen. The corresponding mixed valence state composition is written $Na_3(U_{1-x},Na_x)O_4$ with 0<$\textit{x}$<0.16(2). To complete the data on the Na-U-O system, the thermodynamic functions of $Na_2U_2O_7$ and $Na_4UO_5$ were evaluated using Knudsen effusion mass spectrometry (KEMS) and thermal-relaxation calorimetry. In addition, the oxygen content required at 900 K within liquid sodium to form pentavalent $Na_3UO_4$ and hexavalent $Na_4UO_5$ were calculated to be 0.7 and 1.5 wppm, respectively, which are levels typically encountered in SFRs. A thermodynamic model for the Np-O system was then developed using the CALPHAD method. This is particularly relevant since it is envisaged to incorporate minor actinides into the fuel to minimize the nuclear waste inventory. The poorly known structures of the Na- Np-O and Na-Pu-O phases diagrams, i.e., tetravalent $Na_2AnO_3$ (An=Np,Pu), pentavalent $Na_3AnO_4$, hexavalent $Na_4AnO_5$ and $\alpha-Na_2NpO_4$, and heptavalent $Na_5AnO_6$, were also re-fined by the Rietveld method. The structures of $Na_3NpO_4$ and $Na_3PuO_4$ were determined ab initio from powder X-ray diffraction data, and found to be orthorhombic in the space group $\textit{Fmmm}$. The valence states of the neptunium cations were confirmed from the isomer shift values of their Mössbauer spectra. Having established the charge states without ambiguity, XANES spectra were collected at the $Np-L_3$ and $Pu-L_3$ edges to serve as reference data for An(V), An(VI), and An(VII) oxide phases in the solid state. Finally, KEMS studies of $\alpha-Na_2NpO_4$ showed very promising results for the determination of the enthalpies of formation of the sodium neptunates and plutonates, for which there is almost no data available. The heat capacities and entropies at 298.15 K of $\alpha-Na_2NpO_4$, $Na_4NpO_5$, $Na_5NpO_6$, and $Na_5PuO_6$ were also determined. Comparing their Gibbs energy values, the sodium neptunates were found to be slightly more stable than their isostructural uranium analogues.

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Branford, William Richard. « Relationship of structural and electronic properties in transition metal oxides ». Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.407974.

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Jewell, Catherine Mary. « Structural & ; electronic properties of some early transition metal oxides ». Thesis, University College London (University of London), 2004. http://discovery.ucl.ac.uk/1446632/.

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Low-dimensional spin systems with S = 1/2 and a singlet ground state attract intensive research efforts because of the quantum nature of their ground state. Since the discovery of the singlet plaquette CaV4O9 compound more attention has been paid to chemical analogues with S = 1/2, V4+ (d1) ions. For example, the V2O5 network exhibits the characteristics of layered and crystallographic shear structures and there is a large vanadium oxide bronze family, MxV2O5 (M = alkali, alkaline earth metals), which shows several original [V2O5] networks. For this reason, the atomic architectures of V2O5 and its derivatives provide a stage where various lower-dimensional quantum critical phenomena can be realised. Compounds in the series LixV2O5 were synthesised via soft chemistry methods and characterised structurally and magnetically via high-resolution x-ray and neutron diffraction and magnetization measurements using a SQUID magnetometer. Additional weaker peaks observed in certain of the diffraction patterns suggested the occurrence of charge ordering of vanadium ions in an incommensurately modulated superstructure for some of the E-LixV2O5 and E'-LixV2O5 phases. Having discovered a possible magnetic transition (Tf ~ 25 K) in one of these dilute-spin phases, Li0.50V2O5, believed to be associated with the low-dimensional, chain-like arrangement of the V4+ (S = 1/2, d1) cations over the non-magnetic V5+(S = 0, d0) network, a local probe, SR, was applied to investigate its ground state and the ground states of other members of the series LixV2O5 with x = 0.55, 0.64 and 0.72 which also exhibit interesting magnetic behaviour. Lack of oscillation in the SR data revealed the absence of any long-range magnetic order for Li0.50V2O5, Li0.55V2O5, Li0.64V2O5, and Li0.72V2O5, supportive of a true one-dimensional ground state, suggesting the formation of domains of one-dimensional antiferromagnetic chains, consistent with the Bonner-Fisher model for low-dimensional magnetic behaviour which provided a good fit to the SQUID data collected.

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Mohamed, Hussien Ahmed Abbas. « Structural and electrical properties of zirconia doped with some oxides ». Clausthal-Zellerfeld Papierflieger, 2009. http://d-nb.info/99700701X/04.

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Bharathy, Muktha. « Layered Oxides And Phosphates Of Bismuth : New Structural Types And Related Properties ». Thesis, Indian Institute of Science, 2006. https://etd.iisc.ac.in/handle/2005/284.

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The thesis entitled "Layered Oxides and Phosphates of Bismuth: New Structural Types and Related Properties" consists of three parts and six chapters. It begins with an introductory note providing a brief overview of the existing literature on bismuth based layered oxides. Part A of the thesis describes novel variants of the Aurivillius, Scheelite and Fluorite related phases with special emphasis on photocatalytic behavior of these materials. Chapter 1 describes two new compounds, LiBi4Nb3O14 and LiBi4Ta3O14 characterized by single crystal X-ray diffraction to depict a unique structure, which have similarities with both an ideal Aurivillius phase and a typical hexagonal tungsten bronze. Photo-degradation of a wide range of water pollutants, which include commonly, used dyes in textile industry and phenols suggest selectivity of LiBi4Nb3O14 towards hydroxyl group containing aromatic compounds. Chapter 2, Section 1 presents the structure of BaBi2Mo4O16 as a new compound among Scheelites, which shows high selectivity towards photo-degradation of non- chloro-containing aromatic systems. Further, the degradation rates are found to be significantly higher than the commercial TiO2 catalyst for nitro and methyl phenols. The solid solution, BaBi2Mo4-xWxO16 (0.25 ≤ x ≤ 1) has been analyzed to obtain insights into the compositional aspects. Section 2 has a detailed discussion on the structural stability of the Scheelite BaBi2Mo4O16 upon substitution of divalent cations, Ca, Sr and Pb at the barium site. The potential of these compounds as photocatalytic materials has been investigated. Chapter 3 describes a detailed kinetic analysis along with a single crystal X-ray structure determination of Ba2Bi24Mo10O68. Substitution at the Bi site by Ba and La results in differences in photocatalytic activity. All variants are observed to show specificity towards nitro- substitution at the ortho- position in phenols. Chapter 4 is a re-determination of the crystal structures of the triclinic polymorphs of BiNbO4 and BiTaO4 since one of the earlier reports is on a twinned crystal with large, unacceptable thermal ellipsoids and the other is a powder data -based Rietveld refinement of this model. Further BiNbO4 has been investigated to evaluate selectivity in photo degradation of dyes. In Part B, an attempt to correlate the crystal structure with relaxor ferroelectric behavior is outlined. Chapter 5 investigates a bismuth based tetratungsten bronze (TTB) relaxor material for the first time. Single crystal X-ray diffraction studies on the composition, x = 0.77 of the solid solution, Ba5x/2Bi(1-x)5/3Nb5O15 (0.52 ≤ x ≤ 0.8) depicts disorder in the occupancies of barium and bismuth atoms which is suggested to be the possible origin for relaxor behavior. Dielectric measurements correlate the structural features. Part C consists of a structure-based analysis on possible correlations with ionic conductivity. Chapter 6 describes two new crystal structures, Bi17P8O45.5 and Bi20P8O50, and the evolution of the series, Bi16+xP8O45+(3x-2)/2 (0.7 ≤ x ≤ 4.0). A rationale for the low ionic conductivity exhibited in these materials is arrived at from the arrangement of atoms in the crystal structure. Appendix A consists of a description of the crystal structure and ionic conductivity of Bi3W2O10.5.

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Bharathy, Muktha. « Layered Oxides And Phosphates Of Bismuth : New Structural Types And Related Properties ». Thesis, Indian Institute of Science, 2006. http://hdl.handle.net/2005/284.

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The thesis entitled "Layered Oxides and Phosphates of Bismuth: New Structural Types and Related Properties" consists of three parts and six chapters. It begins with an introductory note providing a brief overview of the existing literature on bismuth based layered oxides. Part A of the thesis describes novel variants of the Aurivillius, Scheelite and Fluorite related phases with special emphasis on photocatalytic behavior of these materials. Chapter 1 describes two new compounds, LiBi4Nb3O14 and LiBi4Ta3O14 characterized by single crystal X-ray diffraction to depict a unique structure, which have similarities with both an ideal Aurivillius phase and a typical hexagonal tungsten bronze. Photo-degradation of a wide range of water pollutants, which include commonly, used dyes in textile industry and phenols suggest selectivity of LiBi4Nb3O14 towards hydroxyl group containing aromatic compounds. Chapter 2, Section 1 presents the structure of BaBi2Mo4O16 as a new compound among Scheelites, which shows high selectivity towards photo-degradation of non- chloro-containing aromatic systems. Further, the degradation rates are found to be significantly higher than the commercial TiO2 catalyst for nitro and methyl phenols. The solid solution, BaBi2Mo4-xWxO16 (0.25 ≤ x ≤ 1) has been analyzed to obtain insights into the compositional aspects. Section 2 has a detailed discussion on the structural stability of the Scheelite BaBi2Mo4O16 upon substitution of divalent cations, Ca, Sr and Pb at the barium site. The potential of these compounds as photocatalytic materials has been investigated. Chapter 3 describes a detailed kinetic analysis along with a single crystal X-ray structure determination of Ba2Bi24Mo10O68. Substitution at the Bi site by Ba and La results in differences in photocatalytic activity. All variants are observed to show specificity towards nitro- substitution at the ortho- position in phenols. Chapter 4 is a re-determination of the crystal structures of the triclinic polymorphs of BiNbO4 and BiTaO4 since one of the earlier reports is on a twinned crystal with large, unacceptable thermal ellipsoids and the other is a powder data -based Rietveld refinement of this model. Further BiNbO4 has been investigated to evaluate selectivity in photo degradation of dyes. In Part B, an attempt to correlate the crystal structure with relaxor ferroelectric behavior is outlined. Chapter 5 investigates a bismuth based tetratungsten bronze (TTB) relaxor material for the first time. Single crystal X-ray diffraction studies on the composition, x = 0.77 of the solid solution, Ba5x/2Bi(1-x)5/3Nb5O15 (0.52 ≤ x ≤ 0.8) depicts disorder in the occupancies of barium and bismuth atoms which is suggested to be the possible origin for relaxor behavior. Dielectric measurements correlate the structural features. Part C consists of a structure-based analysis on possible correlations with ionic conductivity. Chapter 6 describes two new crystal structures, Bi17P8O45.5 and Bi20P8O50, and the evolution of the series, Bi16+xP8O45+(3x-2)/2 (0.7 ≤ x ≤ 4.0). A rationale for the low ionic conductivity exhibited in these materials is arrived at from the arrangement of atoms in the crystal structure. Appendix A consists of a description of the crystal structure and ionic conductivity of Bi3W2O10.5.

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Kawamoto, Takahiro. « Synthesis and Structural Analysis of Metastable Transition Metal Oxides with Unique Magnetic Properties ». 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215553.

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Szkoda, Iwona. « Phase relations, structural studies and physical properties of mixed metal oxides and sulphides ». Thesis, Heriot-Watt University, 2008. http://hdl.handle.net/10399/2212.

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The phase relations in three oxide systems; ZnO–BiVO4, Pb2V2O7–BiVO4 and PbO– BiVO4, have been studied and their phase diagrams over the whole component concentration range up to 1273 K have been established. As a result of solid-state reaction between ZnO and BiVO4 mixed at a molar ratio of 2:1 or among ZnO, V2O5 and Bi2O3, mixed at a molar ratio of 4:1:1, a new double vanadate BiZn2VO6 has been obtained. Its crystallographic system was determined, its unit cell parameters were calculated and its incongruent melting temperature was established. A new compound is also formed in the Pb2V2O7–BiVO4 system. It has been shown that BiVO4 and Pb2V2O7 react with each other forming a compound of the formula Pb2BiV3O11, when their molar ratio is equal to 1:1, or between PbO, Bi2O3 and V2O5, mixed at a molar ratio of 4:1:3. This material melts congruently and it crystallises in the triclinic system. A new series of non-stoichiometric sulphides Ga1-xGexV4S8 (0 x 1) has been synthesised by standard solid-state reaction. The samples have been characterised by powder X-ray and neutron diffraction, SQUID magnetometry and electrical transportproperty measurements. Structural analysis reveals that a solid solution is formed throughout this composition range. Magnetic measurements suggest that the ferromagnetic behaviour of the end-member phase GaV4S8 is retained at x 0.7. By contrast Ga0.25Ge0.75V4S8 appears to undergo antiferromagnetic ordering at ca. 15 K. All materials with x ¹ 1 are n-type semiconductors whose resistivity falls by almost six orders of magnitude with decreasing gallium content, whilst the end-member phase GeV4S8 is a ptype semiconductor. Powder neutron diffraction studies show that the cubic unit cell is retained for non-stoichiometric materials to the lowest temperatures studied. Single crystals of five erbium-chromium sulphides have been grown by chemical vapour transport using iodine as the transporting agent. Single-crystal X-ray diffraction reveals that in Er3CrS6, octahedral sites are occupied exclusively by Cr3+ cations, leading to onedimensional CrS4 5- chains of edge-sharing octahedra, whilst in Er2CrS4, Er3+ and Cr2+ cations occupy the available octahedral sites in an ordered manner. By contrast, in Er6Cr2S11, Er4CrS7 and Er8Cr3S15, Er3+ and Cr2+ ions are disordered over the octahedral sites. In Er2CrS4, Er6Cr2S11, Er4CrS7 and Er8Cr3S15, the network of octahedra generates an anionic framework constructed from M2S5 slabs of varying thickness, linked by onedimensional octahedral chains. This suggests that these four phases belong to a series in which the anionic framework may be described by the general formula [M2n+1S4n+3]x-, with charge balancing provided by Er3+ cations located in sites of high-coordination number within one-dimensional channels defined by the framework. Er4CrS7, Er6Cr2S11, Er8Cr3S15 ii and Er2CrS4 may thus be considered as the n = 1, 2, 3 and members of this series. Whilst Er4CrS7 is paramagnetic, successive magnetic transitions associated with ordering of the chromium and erbium sub-lattices are observed on cooling Er3CrS6 (TC(Cr) = 30 K; TC(Er) = 11 K) and Er2CrS4 (TN(Cr) = 42 K, TN(Er) = 10 K) whereas Er6Cr2S11 exhibits ordering of the chromium sub-lattice only (TN = 11.4 K). These four materials have been studied using neutron diffraction which allowed magnetic ordering to be examined.

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Xiong, Jie. « Investigation of Structural and Magnetic Properties of Perovskite Type Oxides Containing 5d Ions ». The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1492623459123207.

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Hirai, Shigeto. « Investigation of CaIr1-xPtxO3 and CaIr0.5Rh0.5O3 : structural properties, physical properties and stabilising conditions for post-perovskite oxides ». Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/5019.

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Our understanding of the nature of Earth’s D” region was changed significantly by a recent finding by Murakami et al. (2004), who revealed a phase transition from perovskite to post-perovskite structure in MgSiO3 at about 125 GPa and 2500 K, corresponding to conditions of the lowermost mantle. A perovskite to post-perovskite phase transition accounts for many unusual features of the D” region, including its notable seismic anisotropy, and also accounts for the unusual topology of the D” discontinuity. However, the experimentally synthesised post-perovskite phase of MgSiO3 is not quenchable to ambient conditions, which means that many of its physical properties remain difficult to determine. On the other hand, there are several post-perovskite oxides, CaIrO3, CaPtO3, CaRhO3 and CaRuO3, which can be quenched to ambient conditions, maintaining their structure. High pressure synthesis of CaIr1-xPtxO3 solid solutions (x = 0, 0.3, 0.5, 0.7) and CaIr0.5Rh0.5O3 was conducted at the University of Edinburgh and Geodynamics Research Center, Ehime University, and structures and physical properties of these novel post-perovskite materials determined. Substantial [100] grain growth was observed in all solid solutions leading to pronounced texture even in powdered materials. Temperature-independent paramagnetism above 150 K and small magnetic entropy observed in heat capacity measurements suggest that CaIrO3 is an intrinsically weak itinerant ferromagnetic metal, while electrical resistivity measurements show that it is a narrow bandgap semiconductor, possibly due to grain boundary effects. CaIrO3 undergoes a magnetic transition at 108K and possesses a saturated magnetic moment of 0.04 μB. Doping with Pt or Rh induces Curie-Weiss paramagnetism and suppresses the magnetic transition. The anisotropic structure and morphology of CaIrO3 combined with the Ir4+ spin-orbit coupling results in a large magnetic anisotropy constant of 1.77 x 106 Jm-3, comparable to values for permanent magnet materials. A new high-pressure phase of CaIr0.5Pt0.5O3 was synthesised at 60GPa, 1900K using a laser-heated DAC (diamond anvil cell) at GRC, Ehime University. Its Raman spectra resemble those of perovskite phases of CaIrO3 and CaMnO3, implying that CaIr0.5Pt0.5O3 undergoes a post-perovskite to perovskite phase transition with increasing pressure. I estimate an increase in thermodynamic Grüneisen parameter γth across the post-perovskite to perovskite transition of 34 %, with similar magnitude to (Mg,Fe)SiO3 and MgGeO3, suggesting that CaIr0.5Pt0.5O3 is a promising analogue for experimentally simulating the competitive stability between perovskite and post-perovskite phase of magnesium silicates in Earth’s lowermost mantle. Such estimation is reliable since the estimated and directly calculated thermodynamic Grüneisen parameter γth from heat capacity show consistent values. The marked effect that Pt has on stabilising the post-perovskite structure in CaIr1-xPtxO3 solid solutions explains why the post-perovskite to perovskite phase transition has not been observed for CaPtO3 in contrast to other quenchable post-perovskite oxides: CaIrO3, CaRhO3 and CaRuO3.Work presented here demonstrates that CaIrO3 solid solutions can be used to provide new insight into factors stabilising post-perovskite structures in Earth’s lowermost mantle.

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Silva, Antonio Vinnie dos Santos. « Structural, vibrational and morphological properties of La2CoMnO6 multiferroics films ». Universidade Federal do CearÃ, 2016. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=17901.

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Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico
FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico
FundaÃÃo de Amparo Ã Pesquisa e ao Desenvolvimento CientÃfico e TecnolÃgico do MaranhÃo
CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior
Perovskitas duplas com fÃrmula na forma A2BBâO6 (A = La, Sr, Ca, B/Bâ = Co/Mn ou Fe/Mo) sÃo materiais multiferrÃicos de grande interesse na ciÃncia devido Ãs notÃveis propriedades, que permitem aplicaÃÃes em capacitores e em memÃrias, por exemplo. AlÃm disso, mudanÃas estruturais sÃo observadas entre a forma policristalina e o filme fino. Essas propriedades podem mudar de acordo com a rota utilizada para sintetizaÃÃo do material. No nosso trabalho estudamos filmes de La2CoMnO6 sintetizados pelo mÃtodo de Pechini Modificado (MPM), com trÃs deposiÃÃes e tratados em diferentes temperaturas: 700, 800 e 900 ÂC. Os filmes foram caracterizados por difraÃÃo de raios X, Microscopia EletrÃnica de Varredura (MEV), Microscopia de ForÃa AtÃmica e espectroscopia Raman Ã temperatura ambiente e tambÃm variando a temperatura. As tÃcnicas de MEV e AFM foram bastante eficientes na determinaÃÃo do diÃmetro mÃdio dos filmes, fornecendo resultados correspondentes. A tÃcnica de EDS trouxe dados qualitativos da composiÃÃo do material. A difraÃÃo de Raios X confirmou a fase do filme, alÃm de ter identificado a composiÃÃo do substrato: silÃcio e platina. A espectroscopia Raman em diversos pontos possibilitou identificar a regiÃo de melhor formaÃÃo do LCMO. O estudo da mudanÃa do fÃnon mais intenso com a temperatura mostrou diferentes temperaturas para a transiÃÃo de fase paramagnÃtica-ferromagnÃtica, possibilitando confirmar que a temperatura de calcinaÃÃo dos filmes determinou elevada desordem estrutural para os filmes de LCMO tratados a 700 e 900 ÂC. Discutimos nossos resultados com outros estudos na literatura, que mostram as medidas magnÃticas como um fator determinante para comprovar a temperatura do acoplamento spin-fÃnon.

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Grant, Stacy M. « Polymer Templating Synthesis, Adsorption and Structural Properties of Alumina-Based Ordered Mesoporous Materials ». Kent State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=kent1317593306.

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Das, Supriyo. « Synthesis and structural, magnetic, thermal, and transport properties of several transition metal oxides and arsenides ». [Ames, Iowa : Iowa State University], 2010. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3403075.

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Aguesse, Frederic. « Structural, electrical and magnetic properties of CoFe2O4 and BaTiO3 layered nanostructures on conductive metal oxides ». Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9300.

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Multiferroic materials exhibit simultaneously, magnetic and electric order. In a magnetoelectric composite structure, a coupling is induced via an interfacial elastic interaction between magnetostrictive and piezoelectric materials enabling the control of the magnetisation by applying an electric field and vice versa. However, despite the potential of such coupling, experimental limits of theoretical models were observed. This work sheds some light on these limits by focusing the research on the chemistry of nanocomposite CoFe2O4 and BaTiO3, particularly at the interfaces where the coupling predominates. A comparison of the most common conductive oxides, Nb doped SrTiO3 and SrRuO3, was made for the bottom electrode application. The variation of conductive properties in Nb-SrTiO3 thin films at high temperature has been quantified when artificially strained and 60 nm SrRuO3 film was found to be the best bottom electrode choice for room temperature use. Epitaxial growth of magnetic CoFe2O4 was achieved on various metal oxide substrates despite large lattice mismatches. Crystallographic properties and strain evaluation were investigated and a Stranski-Krastanov growth mechanism, arising from the PLD deposition, was predominant. A notable drop of magnetisation was observed depending on the growth template, particularly on BaTiO3 substrates, the piezoelectric counterpart of the magnetoelectric structures. However, an encouraging magnetoelectric coupling induced by thermal phase transition of BaTiO3 was revealed. For BaTiO3, a control of the growth direction was realised by varying the deposition pressure, and the existence of both 180° and 90° ferroelectric domains was observed for films up to 300 nm in thickness. However, both the ferroelectric and piezoelectric properties were reduced in the thin films due to the clamping effect of the substrate. Finally, highly crystalline multilayers of CoFe2O4 and BaTiO3 were prepared on SrRuO3 buffered SrTiO3 substrates. It was found that the degradation of both magnetic and ferroelectric properties was proportional to the increase in the number of interfaces. A thorough microscopic study revealed interdiffusion and chemical instability occurring between CoFe2O4 and BaTiO3 at the interface. This undesired effect was partially recovered by the insertion of an ultra thin layer of SrTiO3, acting as a barrier layer at every interface. This research shows how interfacial chemistry need to be understood to achieve high magnetoelectric coupling in these types of epitaxial engineered structures.

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Andersson, Martin. « Structural, thermal and thermodynamic properties of some Ln-Pd oxides and their behaviour as catalyst precursors ». Doctoral thesis, Stockholms universitet, 1999. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-64279.

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The structural, thermal and thermodynamic properties of some Ln-Pd oxides of the Ln4Pd07 type are presented. The main results are; (i) Reduction of Ln4Pd07, either ex-situ by CO or in-situ by a synthetic car exhaust gas, results in a materialwith catalytic activity for car exhaust gas clean-up reactions. The obtained material consists of Pd nanoparticles situated on the surface of micron-sized grains of Ln2O3 Upon heat treatment of the reduced material in air, Lu4Pd07 i srapidly re-formed. This property May be utilised for reactivation/conditioning of aged Ln4Pd07-based catalysts; (ii) The Ln4Pd07 compounds with Ln = Nd, Sm, Eu and Gd dare isostructural and have a structure which is a triclinic distortion of the monoclinic La4Pd07 type; (iii) ΔH°, and ΔS ° f values for La4Pd07 and Nd4Pd07 have been calculated by a combination of data obtained from dissolution calorimetry and thermogravimetric analysis studies; ( iv ) Carbon nanotubes, having the so-called fishbone structure, can be prepared by heat treatment o f La4Pd07 in a 20% CO/He gas mixture for an extended period of time. Nanotubes have been extracted from the obtained La203/Pd/nanotube mixture, using a wet-chemical method.

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Halpegamage, Sandamali. « Surface Properties of Titanium dioxide and its Structural Modifications by Reactions with Transition Metals ». Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6510.

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Surfaces of metal oxides play a vital role in many technologically important applications. The surfaces of titanium dioxide, in particular, show quite promising properties that can be utilized in solid-state gas sensing and photocatalysis applications. In the first part of this dissertation we investigate these properties of TiO2 surfaces through a vigorous surface scientific approach. In the second part, we investigate the possibilities of modifying the TiO2 surfaces by depositing multi-component transition metal oxide monolayers so that the properties of bare TiO2 surface can be influenced in a beneficial way. For instance, via formation of new surface sites or cations that have different valance states, the chemisorption and catalytic properties can be modified. We use sophisticated experimental surface science techniques that are compatible with ultra-high vacuum technology for surface characterization. All the experimental results, except for the photocatalysis experiments, were compared to and verified by supporting DFT-based theoretical results produced by our theory collaborators. TiO2 based solid-state gas sensors have been used before for detecting trace amounts of explosives such as 2,4-dinitrololuene (DNT), a toxic decomposition product of the explosive 2,4,6-trinitrotoluene (TNT) that have very low vapor pressure. However, the adsorption, desorption and reaction mechanism were not well- understood. Here, we investigate 2,4-DNT adsorption on rutile-TiO2(110) surface in order to gain insight about these mechanisms in an atomistic level and we propose an efficient way of desorbing DNT from the surface through UV-light induced photoreactions. TiO2 exists in different polymorphs and the photocatalytic activity differs from one polymorph to another. Rutile and anatase are the most famous forms of TiO2 in photocatalysis and anatase is known to show higher activity than rutile. The photoactivity also varies depending on the surface orientation for the same polymorph. So far, a reasonable explanation as to why these differences exist was not reported. In our studies, we used high quality epitaxial rutile and anatase thin films which enabled isolating the surface effects from the bulk effects and show that it is the difference between the charge carrier diffusion lengths that causes this difference in activities. In addition to that, using different surface orientations of rutile-TiO2, we show that the anisotropic bulk charge carrier mobility may contribute to the orientation dependent photoactivity. Moreover, we show that different surface preparation methods also affect the activity of the sample and vacuum reduction results in an enhanced activity. In an effort to modify the TiO2 surfaces with monolayer/mixed monolayer oxides, we carried out experiments on (011) orientation of single crystal rutile TiO2 with few of the selected transition metal oxides namely Fe, V, Cr and Ni. We found that for specific oxidation conditions a monolayer mixed oxide is formed for all M (M= Fe, V, Cr, Ni), with one common structure with the composition MTi2O5. For small amounts of M the surface segregates into pure TiO2(011)-2×1 and into domains of MTi2O5indicating that this mixed monolayer oxide is a low energy line phase in a compositional surface phase diagram. The oxygen pressure required for the formation of this unique monolayer structure increases in the order of V2O5 mixed monolayer oxide by DFT-based simulations was verified by X-ray photoemission diffraction measurements performed at a synchrotron facility.

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Burriel, López Mónica. « Epitaxial Thin Films of Lanthanum Nickel Oxides : Deposition by PI-MOCVD, Structural Characterization and High Temperature Transport Properties ». Doctoral thesis, Universitat Autònoma de Barcelona, 2007. http://hdl.handle.net/10803/3246.

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En los últimos años ha habido un interés creciente en el estudio de el compuesto La2NiO4+?, debido a sus propiedades como conductor mixto iónico-electrónico, que lo hacen adecuado para su utilización en dispositivos electroquímicos, tales como cátodo para pilas de combustible de óxido sólido a temperaturas intermedias (IT-SOFC), membranas de permeación o sensores de gas. La estructura de fase La2NiO4+? está formada por láminas de LaNiO3, de tipo perovskita, alternadas con láminas de LaO de tipo cloruro sódico, en las cuales puede incorporarse oxígeno sobreestequiométrico. Esta estructura laminar es la responsable de la anisotropía en las propiedades del La2NiO4+?, dando lugar a una conductividad iónica y electrónica que es entre dos y tres órdenes de magnitud superior a lo largo del plano ab, en comparación con la dirección del eje c.
Este trabajo consiste en el estudio, desde un punto de vista fundamental, de películas delgadas epitaxiales de La2NiO4+? orientadas a lo largo del eje c y crecidas por la técnica de deposición química en fase vapor de precursores organometálicos por inyección pulsada (PI-MOCVD) sobre diferentes sustratos, con el fin de adquirir una mejor comprensión de sus características microestructurales, su variación con la tensión y la influencia de la tensión en las propiedades de transporte a elevada temperatura. Además, el crecimiento epitaxial permite la medida de las propiedades de las películas de La2NiO4+? en dos direcciones perpendiculares, obteniendo una medida directa de la anisotropía del material.
El La2NiO4+? es el primer miembro (n = 1) de la familia Ruddlesden-Popper Lan+1NinO3n+1, en la que la estructura de cada miembro está formada por un número n de bloques perovskita LaNiO3 alternados entre bloques LaO tipo cloruro sódico. Asimismo se han intentado depositar películas orientadas a lo largo del eje c de los miembros n = 2, 3 e ?, y se ha estudiado la variación las propiedades de transporte a lo largo de la serie Lan+1NinO3n+1.
En la tesis se realiza una introducción a los conductores mixtos iónicos-electrónicos (MIEC) y a los cátodos para pilas de combustible de óxido sólido (SOFC), como una posible aplicación del material La2NiO4+?. Se describen las propiedades más importantes de la fase La2NiO4+?, y de los miembros n =2, 3 e ? de la familia Lan+1NinO3n+1, así como el estado del arte de la preparación de películas delgadas de estos materiales.
A continuación se describe la técnica de deposición química en fase vapor de precursores organometálicos por inyección pulsada (PI-MOCVD), acompañada de una descripción detallada de los parámetros de depósito seleccionados, y del equipo PI-MOCVD utilizado. También se describen las técnicas utilizadas en la caracterización de las películas delgadas de Lan+1NinO3n+1.
Posteriormente se describen los parámetros de depósito optimizados para la deposición de películas epitaxiales de La2NiO4+? y se realiza una caracterización estructural, morfológica y microestructural en función del espesor de las películas, del sustrato utilizado y de la temperatura. También se detalla y describe la conductividad total de películas epitaxiales de diferente espesor medida. Para éstas películas se han medido, además, las propiedades de intercambio y de difusión de oxígeno utilizando dos técnicas diferentes: la técnica de intercambio de isótopos y la técnica de relajación de la conductividad. Los resultados de estas medidas se discuten en función de la microestructura de las películas.
Por último, se ha completado el estudio describiendo los primeros resultados de deposición de otros miembros de la familia Ruddlesden-Popper. La evolución de las propiedades de transporte total de las películas delgadas de Lan+1NinO3n+1 se han relacionado con el número de láminas tipo perovskita n.
In the last years there has been a great interest in the study of the La2NiO4+? compound due to its mixed ionic-electronic properties, which make it suitable in electrochemical devices, such as cathode in Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC), permeation membranes or gas sensors. The La2NiO4+? phase structure is formed by perovskite-type LaNiO3 layers alternated with rocksalt-type LaO layers, in which hyperstoichiometric oxygen can be incorporated. This layered structure is responsible for the anisotropy in the La2NiO4+? properties, leading to electronic and ionic conductivity three orders of magnitude higher along the ab plane, in comparison with the c-axis direction.
This work is focused on the study, from a fundamental point of view, of epitaxial c-axis oriented La2NiO4+? thin films deposited by PI-MOCVD technique on different substrates, in order to achieve a better comprehension of the microstructural characteristics, their variation with strain and their influence in its high temperature transport properties. Moreover, the epitaxial growth of the films permits the measurement of the properties of the La2NiO4+? in two perpendicular directions, to have a direct inset of the anisotropy.
The La2NiO4+? phase is the n = 1 member of the Lan+1NinO3n+1 Ruddlesden-Popper family, in which the structure of each member is formed by a n number of perovskite layers alternated between rock-salt layers. We have also attempted to deposit c-axis oriented films of the n = 2, n = 3 and n = 1 members and studied the variation of the transport properties through the different members of the family.
First, Chapter 1 consists of an introduction to the mixed ionic-electronic conductors (MIEC) and to the solid oxide fuel cell (SOFC) cathodes, as a possible application of the La2NiO4+? material. The most remarkable properties of the La2NiO4+? phase, and of the n = 2, 3 and 1 members of the Lan+1NinO3n+1 family are analyzed, as well as the state of the art in the preparation of thin films of these materials.
In Chapter 2, the Metalorganic Chemical Vapor Deposition (MOCVD) technique is described, accompanied by a detailed description of the selected experimental deposition parameters and of the Pulsed Injection MOCVD equipment used. Chapter 3 summarizes all the techniques used for the Lan+1NinO3n+1 thin film characterization.
In Chapter 4, the optimized experimental parameters for the deposition of epitaxial La2NiO4+? thin films are described. Structural, morphological and microstructural characterization is performed as a function of film thickness, substrate used and temperature. Total conductivity of epitaxial layers is also described and discussed.
In Chapter 5 we have studied the oxygen exchange and transport of the La2NiO4+? thin films by two different techniques: the oxygen isotope exchange and the electrical conductivity relaxation. Results are discussed as a function of microstructure.
Finally, in Chapter 6, the study is completed describing the first results of the deposition of the other members of the Ruddlesden-Popper family. Evolution of the total conductivity properties of the Lan+1NinO3n+1 films has been related to the n number of perovskite layers.

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Benadda, Amel, Amar Djadoun, Hafida Guessis et Akila Barama. « Effect of the Preparation Method on the Structural and Catalytic Properties of MnOx-CeO2 Manganese Cerium Mixed Oxides ». Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35257.

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MnOx-CeO2 catalysts (molar ratio Mn/Ce 1) were prepared using two methods: co-precipitation and citrate methods. The prepared solids were calcined at 500°C, and characterized by XRD, nitrogen adsorp-tion-desorption technique and SEM morphological, they were, then, tested in the toluene combustion reac-tion. The catalytic performances of the prepared solids were evaluated in the temperature range 150-400°C. The XRD analysis of the two solids showed that the only crystalline phase detected is cerium oxide. BET surface area measurements showed that the incorporation of manganese led to an increase in the spe-cific surface area of ceria, the solid prepared by the co-precipitation method led to the highest specific sur-face area (156 m²/g). The solids showed good performances in the toluene combustion reaction that depend strongly on the preparation method. The best catalytic activity was obtained for the catalyst prepared by the citrate method achieving a complete conversion of toluene at 250 ° C. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35257

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Burriel, López Mónica. « Epitaxial thin films of lanthanum nickel oxides deposition by PI-MOCVD, structural characterization and high temperature transport properties ». Saarbrücken VDM Verlag Dr. Müller, 2007. http://d-nb.info/988631342/04.

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Leduc, Jennifer [Verfasser]. « Chemical Processing of Nanostructured Uranium Oxides for Solar Energy Conversion : Investigations on Structural, Electronic and Photoelectrochemical Properties / Jennifer Leduc ». München : Verlag Dr. Hut, 2018. http://d-nb.info/1162767715/34.

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31

Green, Sara. « Electrochromic Nickel – Tungsten Oxides : Optical, Electrochemical and Structural Characterization of Sputter-deposited Thin Films in the Whole Composition Range ». Doctoral thesis, Uppsala universitet, Fasta tillståndets fysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-179764.

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This thesis investigates the electrochromic NixW1-x oxide thin film system, where 0 < x < 1. The thin films were deposited by reactive DC magnetron co-sputtering from one Ni and one W metal target. In addition, Ni oxide was deposited with water vapor added to the sputtering gas. The different compositions were structurally characterized by X-ray diffraction, X-ray photoelectron-, Rutherford backscattering- and Raman spectroscopy. Possible nanostructures were studied by ellipsometry together with effective medium theory. Optical and electrochemical properties were investigated by spectrophotometry and cyclic voltammetry in 1 M lithium perchlorate in propylene carbonate (Li-PC). Li-PC electrolyte was used as it is being compatible with both W and Ni oxides. Few studies have previously been made on Ni oxides in Li-PC. Films with high Ni content, 0.85 < x < 1, were polycrystalline and all other films were amorphous. W-rich films, x < 0.5, consisted of a mixture of W oxide and NiWO4 -phases, and the Ni-rich samples, x > 0.5, probably consisted of hydrated Ni oxide and NiWO4 -phases. Films with 0 < x < 0.3 showed electrochromic properties similar to W oxide, and films with 0.7 < x < 1 behaved as Ni oxide. For 0.4 < x < 0.7 no optical change was seen. At the border of cathodic electrochromic and non-electrochromic behavior, i.e. x ~ 0.4, the sample behaved as an optically passive intercalation material. The transmittance change was 0.45 and 0.15 for the W-rich and Ni-rich films, respectively. Ni addition to W oxide improved the coloration efficiency. For the Ni-rich films the charge insertion/extraction and optical modulation was low and an aging effect resulted in strong bleaching of the samples. The advantage of W addition to Ni oxide was that the transparency at the bleached state was enhanced. Moreover, it was found that the hydrous character of the Ni oxide had a large impact on the electrochromic performance, both when electrochemically cycled in KOH and in the non-aqueous Li-PC.

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Eichel, Rüdiger-A. « Multi-Frequency and multi-pulse EPR spectroscopy for the study of structural and dynamic properties of defect centers in perovskite oxides ». Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-186665.

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33

Eichel, Rüdiger-A. « Multi-Frequency and multi-pulse EPR spectroscopy for the study of structural and dynamic properties of defect centers in perovskite oxides ». Diffusion fundamentals 12 (2010) 21, 2010. https://ul.qucosa.de/id/qucosa%3A13873.

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34

Ebdah, Mohammad A. « Engineering of the Optical, Structural, Electrical, and Magnetic Properties of Oxides and Nitrides of In-Ga-Zn Thin Films Using Nanotechnology ». Ohio University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1305141588.

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35

Podpirka, Adrian Alexander. « Studies on Synthesis, Structural and Electrical Properties of Complex Oxide Thin Films : Ba1-xSrxTiO3 and La2-xSrxNiO4 ». Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10247.

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High performance miniaturized passives are of great importance for advanced nanoelectronic packages for several applications including efficient power delivery. Low cost thin film capacitors fabricated directly on package (and/or on-chip) are an attractive approach towards realizing such devices. This thesis aims to explore fundamental frequency dependent dielectric and insulating properties of thin film high-k dielectric constant in the perovskite and perovskite-related complex oxides. Throughout this thesis, we have successfully observed the role of structure, strain and oxygen stoichiometry on the dielectric properties of thin film complex oxides, allowing a greater understanding of processing conditions and polarization mechanisms. In the first section of the thesis, we explore novel processing methods in the conventional ferroelectric, barium strontium titanate, $Ba_{1-x}Sr_xTiO_3 (BST)$, using ultraviolet enhanced oxidation techniques in order to achieve improvements in the dielectric properties. Using this method, we also explore the growth of BST on inexpensive non-noble metals such as Ni which presents technical challenges due to the ability to oxidize at high temperatures. We observe a significant lowering of the dielectric loss while also lowering the process temperature which allows us to maintain an intimate interface between the dielectric layer and the metal electrode. The second section of this thesis explores the novel dielectric material, Lanthanum Strontium Nickelate, $La_{2-x}Sr_xNiO_4 (LSNO)$, which exhibits a colossal dielectric response. For the first time, we report on the colossal dielectric properties of polycrystalline and epitaxial thin film LSNO. We observe a significant polarization dependence on the microstructure due to the grain/grain boundary interaction with charged carriers. We next grew epitaxial films on various insulating oxide substrates in order to decouple the grain boundary interaction. Here we observed substrate dependent dielectric properties associated with induced strain. We also observe, due to the p-type carriers in LSNO, pn junction formation when grown epitaxially on the conducting oxide degenerate n-type Nb-doped $SrTiO_3$. Finally we explore the growth mechanism of epitaxial LSNO as a function of high oxygen content. Due to the ability for LSNO to take in interstitial oxygen, a reoriented growth is observed at a critical thickness, thereby allowing us to vary anisotropy as a function of deposition conditions.
Engineering and Applied Sciences

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O'Malley, Matthew John. « A Structural, Bonding, and Properties Study of the Ordered Rock Salt Structures Li₂MO₃ (M = Ru, Ir, Pt) ». The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1250526178.

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37

RIBEIRO, THATIANA G. D. « Sintese e caracterizacao de nanoparticulas magneticas de oxidos mistos de MnFesub(2)Osub(4) recobertas comm quitosona. Estudos da influencia na dopagem com Gdsup(3+) nas propriedades estruturais e magneticas ». reponame:Repositório Institucional do IPEN, 2008. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11515.

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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38

Grund, Bäck Lina. « Redox reactions and structure - properties relations in mixed alkali/alkaline earth glasses : - The role of antimony oxides during the fining process- A structural study of copper(I) and copper(II) ». Doctoral thesis, Linnéuniversitetet, Institutionen för byggd miljö och energiteknik (BET), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-46782.

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It is important to optimize glass compositions for their specific purpose but also for the efficiency of the production process, the manufacturing of glass. This will be beneficial economically and environmentally. Today many processes and glass compositions are already optimized, but due to more strict legislation on toxic elements and substances there must be changes in many glass compositions. One of these elements is antimony; the oxide is used as fining agent to obtain a bubble free glass within a reasonable process time. One aim with this thesis is to obtain a deeper understanding of the fining mechanism in 20R2O-10MO-70SiO2 (R=Na and/or K, M = Ca and/or Ba, Mg, Sr) glasses in order to minimise the amount of Sb2O3. Another intention is to study the structure of 20R2O-10CaO-70SiO2 (R = Na, K) with Cu2+ as probe ion and thus get a deeper knowledge of the surrounding glass matrix. The optical basicity scale is used to determine the acid/base character of the different glass compositions. Fining efficiency results showed a remarkable increase of the number of remaining bubbles when the glass contains either approximately equal amounts of Na and K or Ca and Ba, Mg or Sr. The much higher number of bubbles in the potassium containing glasses compared to the sodium containing is explained by the increase in viscosity, the increase in optical basicity and thus lower oxygen activity. The differences in the fining efficiency when altering alkaline earth ions cannot be explained by the optical basicity values, it seems to be a more complicated situation. This thesis also reports maximum in Vickers hardness and packing density as well as minimum in glass transition temperature for the mixed alkali glasses. The mixed alkaline earth glasses do not exhibit any clear nonlinear behaviour. Raman spectroscopy measurements showed a variation in the network connectivity which has a clear relation to the optical basicity of the different glass compositions. The combination of UV-Vis-NIR and X-ray absorption spectroscopy measurements showed that the coordination sphere for Cu(II) is a tetragonal distorted octahedron with two elongated Cu-O bonds along the z axis. There were no trends in the degree of tetragonal distortion, thus it was about the same for all the investigated glass compositions. Cu(I) is found to be coordinated by two oxygen ligands in mainly linear coordination sphere, evidenced from X-ray absorption spectroscopy.

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SENE, FRANK F. « Sintese e caracterizacao de vidros niobofosfato de bario e potassio para aplicacoes como matriz hospedeira de ions de terras raras ». reponame:Repositório Institucional do IPEN, 2002. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10990.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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40

Bikowski, Andre. « The relation between the deposition process and the structural, electronic, and transport properties of magnetron sputtered doped ZnO and Zn1-xMgxO films ». Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2014. http://dx.doi.org/10.18452/16994.

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In dieser Dissertation wurde die Beziehung zwischen den strukturellen, optischen und Ladungstransporteigenschaften von dotierten ZnO- und Zn1-xMgxO-Schichten eingehend untersucht. Das Ziel war es, die oben genannten Zusammenhänge weiter aufzuklären, wodurch sich anschließend Ansätze für eine zielgerichtete Verbesserung der Schichteigenschaften ableiten lassen. Zunächst konzentriert sich die Arbeit auf das Wachstum der ZnO-Schichten, um wichtige strukturelle Parameter, wie zum Beispiel Korngrößen und Defektdichten, mittels Röntgendiffraktometrie und Transmissionselektronenmikroskopie zu bestimmen. Diese strukturellen Parameter wurden dann als Modellparameter für die theoretische Modellierung des Transports der freien Ladungsträger verwendet. Temperaturabhängige Hall-, Leitfähigkeits- und Seebeck-Koeffizient-Messungen zeigten, dass der elektrische Transport hauptsächlich durch die Streuung der Ladungsträger an ionisierten Störstellen und Korngrenzen limitiert wird. Im Rahmen dieser Arbeit wurde die theoretische Beschreibung der Streuung an Korngrenzen auf entartet dotierte Halbleiter erweitert. Diese Ergebnisse wurden dann genutzt, um ein qualitatives Modell zu formulieren, welches den Zusammenhang zwischen dem Magnetron-Sputter-Abscheidungsprozess und den strukturellen und elektrischen Eigenschaften der Schichten herstellt. Gemäß diesem Modell sind die Schichteigenschaften bei niedrigen Abscheidungstemperaturen hauptsächlich durch die Bildung akzeptoratiger Sauerstoffzwischengitterdefekte bestimmt, die einen Teil der extrinsischen Dotanden kompensieren. Diese Defekte werden durch ein Bombardement der wachsenden Schicht mit hochenergetischen negativen Sauerstoffionen verursacht. Bei höheren Abscheidungstemperaturen dominiert die Bildung von sekundären Phasen oder Defektkomplexen, in denen der Dotant elektrisch inaktiv ist.
In this thesis, the relation between the structural, optical, and charge carrier transport properties of magnetron sputtered doped ZnO and Zn1-xMgxO films has been investigated in detail. The objective was to clarify the above mentioned relations, which allows to derive solutions for a deliberate improvement of the layer properties. The work first focusses on the growth of the ZnO layers to determine important structural properties like grain sizes and defect densities via X-ray diffraction and transmission electron microscopy investigations. These structural properties were then used as model parameters for the theoretical modelling of the charge carrier transport. The temperature dependent Hall, conductivity and Seebeck coefficient measurements show that the transport is mainly limited by grain boundary scattering and ionized impurity scattering. The theoretical description of the grain boundary scattering has been extended in this work to also include degenerate semiconductors. Based on the results on the structural and electronic properties, in a next step a qualitative model was developed which explains the correlation between the magnetron sputtering deposition process and the structural and electronic properties of the films. According to this model, the properties of the films are mainly influenced by the formation of electrically active acceptor-like oxygen interstitial defects at low deposition temperatures, which lead to a partial compensation of the extrinsic donors. These defects are caused by a bombardment of the growing film by high-energetic negative oxygen ions. At higher deposition temperatures, the formation of secondary phases or defect complexes, in which the dopant is electrically inactive, prevails.

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Amorim, Carlos de Oliveira. « Experimental and modeling studies of magnetoelectric multiferroic heterostructured materials ». Doctoral thesis, 2019. http://hdl.handle.net/10773/27751.

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Multiferroic materials are a very exotic type of materials which present simultaneously two or more ferroic properties. Magnetoelectric multiferroics, in particular, are a very prominent class of materials, mainly due to their outstanding foreseen applications such as magnetic sensors, energy harvester/conversion devices, and high efficiency memories. However, intrinsic magnetoelectric materials are quite rare and do not have, yet, the adequate properties to the everyday applications. One of the reasons for this to occur is due to the requirements for magnetism and ferroelectricity in matter being a priori contradictory, since the former needs unfilled dn orbitals, while the latter favours d0 orbitals. Nevertheless, extrinsic magnetoelectric multiferroics do not suffer from this problem because they do not share the same phase, hence being a very promising approach to engineer adequate magnetoelectric multiferroics. This thesis focus on the study of Fe and BaTiO3 systems as a means of achieving novel magnetoelectric effects. It is shown that a peculiar type of BaTiO3:Fe auto-composite presents an ordered magnetic behaviour, despite the concentration of Fe being as low as 113 atomic ppm. The Fe magnetization displays two abrupt changes in its spontaneous value, one with M/M ≈ 32% and the other with M/M ≈ 14%. These magnetic transitions are correlated the BaTiO3 orthorhombic↔tetragonal and tetragonal↔cubic ferroelectric phase transitions. This magnetoelectric auto-composite was the motivation to resort to Density Functional Theory (DFT) modeling as a means to discover the microscopic mechanism(s) behind such a strong magnetoelectric effect. The study of an iron monolayer placed upon several possible BaTiO3 unit cells lead to the discovery of several interfaces with abrupt changes in their spontaneous magnetization, either through the enhancement and reduction of the Fe magnetic moments, or through the change between antiferromagnetic and ferromagnetic order of the Fe monolayer. However, the highlight of these DFT studies lies in the discovery of a particular kind of interfaces, namely in the BTO221_2ndFe and BTO99_2ndFe supercells, where there is a High-Spin–Low-Spin state transition which can quench completely the atomic magnetic moment of each of Fe atom, depending on the local crystal field felt by the Fe atoms. Based on this specific effect, where it is possible to turn on and off the magnetic moments of the Fe atoms, a magnetoelectric multiferroic device was proposed. Knowing the importance of the crystal field for the High-Spin–Low-Spin state transition, a thorough study regarding the Electric Field Gradient (EFG) of each possible BaTiO3 site was performed, resorting to a combined study of DFT and Perturbed Angular Correlations (PAC) spectroscopy. In this study, it was concluded that the PAC spectroscopy is not the most adequate hyperfine technique to be used in a quantitative study of the BaTiO3/Fe interfaces EFG tensor, due to the non-negligible effects of the radioactive probe on the BaTiO3 matrix. Finally, the deposition of BTO/Fe heterostructures on LaAlO3, MgO, Al2O3 and SrTiO3 substrates using RF-Sputtering, and the Molecular Beam Epitaxy (MBE) deposition of Fe layers on BaTiO3 cut at the (100), (110) and (111) planes were performed as an attempt to recreate the interfaces with the most appealing magnetoelectric effects predicted in the DFT modeling. The thin films deposited using sputtering showed the growth of many Fe, Ba-Ti-O and Fe-Ti-O oxides depending strongly on their substrate, as well as in the deposition and annealing conditions. Still no magnetoelectric coupling was observed in such thin films. On the other hand the Fe thin films deposited on BaTiO3 substrates showed large magnetoelectric couplings between the BaTiO3 ferroelectric phase transitions and the magnetization of the Fe layers (similarly to what happened in the BaTiO3:Fe auto-composite). The magnitude of this magnetoelectric couplings is strongly correlated with the BTO interface where the Fe was deposited, showing a huge change in spontaneous magnetization and coercivity for the rhombohedral↔orthorhombic ferroelectric phase transition up to M/M ≈ 148% and HC/HC ≈ 183% respectively for the (110) case.
Materiais Multiferróicos são um tipo de materiais bastante exótico que apresentam simultaneamente dois ou mais tipos de propriedades ferróicas. Multiferróicos magnetoelétricos, em particular, são uma classe de materiais muito proeminente, principalmente devido às suas espantosas aplicações tecnológicas, tais como sensores magnéticos, dispositivos de conversão/colheita de energia, e memórias the alta eficiência. Todavia, materiais magnetoelétricos intrínsecos são verdadeiramente raros e ainda não possuem propriedades adequadas ao uso do dia-a-dia. Uma das razões para que isto aconteça prende-se com o facto dos requisitos para existência de magnetismo e ferroeletricidade na matéria serem a priori contraditórios, uma vez que enquanto os primeiros necessitam de orbitais dn semipreenchidas, os últimos tendem a favorecer orbitais d0. Porém, Multiferróicos magnetoelétricos extrínsecos não sofrem desta limitação pois não partilham a mesma fase sendo portanto uma abordagem promissora para a construção de um bom Multiferróico magnetoelétrico. Esta tese focar-se-á no estudo de sistemas contendo Fe e BaTiO3 como meio de se alcançarem novos efeitos magnetoelétricos. Um auto-compósito de BaTiO3:Fe é apresentado, que apesar da sua diminuta concentração de Fe (apenas 113 ppm atómicas), ainda assim apresenta um comportamento magnético ordenado. A magnetização do Fe apresenta duas variações bruscas no seu valor espontâneo, uma com M/M ≈ 32% e outra com M/M ≈ 14%. Estas transições magnéticas estão correlacionadas com as transições de fase ferroelétricas do BaTiO3 (ortorrômbica↔tetragonal e tetragonal↔cúbica). Este auto-compósito magnetoelétrico foi a motivação par ao uso da Teoria de Densidade Funcional (DFT) como meio para descobrir os mecanismos microscópicos por trás deste acoplamento magnetoelétrico tão intenso. O estudo de uma mono-camada de Fe colocada sobre várias células unitárias de BaTiO3 levaram à descoberta de várias interfaces com mudanças abruptas na sua magnetização espontânea, ora através do aumento ou diminuição dos momentos magnéticos do Fe, ora através da mudança entre a natureza antiferromagnética ou ferromagnética da camada de Fe. Contudo, o destaque dos estudos de DFT reside na descoberta de um tipo particular de interfaces onde ocorre uma transição de estado High-Spin–Low-Spin que consegue colapsar completamente o momento magnético atómico dos átomos de Fe, dependendo do campo cristalino local sentido por esses mesmos átomos. Baseado neste efeito, um dispositivo Multiferróico magnetoelétrico foi proposto. Sabendo a importância do campo cristalino para as transições de estado High-Spin–Low-Spin state, um estudo minucioso foi feito relativo ao gradiente de campo elétrico (EFG) nos sítios possíveis do BaTiO3, usando um estudo combinado entre Correlações Angulares Perturbadas (PAC) e DFT. Neste estudo, concluiu-se que PAC não é uma técnica hiperfina adequada para o estudo quantitativo do tensor EFG de interfaces de BaTiO3/Fe, dados os efeitos não desprezáveis das sondas radioativas na matriz de BaTiO3. Finalmente, foi feita a deposição de Heteroestruturas de BTO/Fe em substratos de LaAlO3, MgO, Al2O3 e SrTiO3 usando RF-Sputtering, assim como deposição de camadas de Fe em substratos de BaTiO3 cortados nos planos (100), (110) e (111) planes, usando Molecular Beam Epitaxy (MBE), numa tentativa de recrear as interfaces com efeitos magnetoelétricos mais apelativos, previstos pela modelação DFT. Os filmes finos depositados por sputtering mostraram o crescimento de múltiplos óxidos de Fe, Ba-Ti-O e Fe-Ti-O dependendo fortemente do substrato onde foram crescidos, assim como das condições de deposição e tratamentos térmicos. Porém, nenhum efeito magnetoelétrico foi observado nestes filmes. Por outro lado, os filmes depositados nos substratos de BaTiO3 mostraram grandes acoplamentos magnetoelétricos entre as fases ferroelétricas do BTO e a magnetização das camadas de Fe (à semelhança do que aconteceu no auto-compósito de BaTiO3:Fe). A ordem de grandeza destes acoplamentos está fortemente correlacionada com a interface do BTO onde o Fe foi depositado, apresentando uma enorme variação na magnetização espontânea e na coercividade para o caso da transição romboédrica↔ortorrômbica, até M/M ≈ 148% e HC/HC ≈ 183% respetivamente para o caso da orientação (110).
Tese realizada com apoio financeiro da FCT através da bolsa SFRH/BD/93336/2013.
Programa Doutoral em Física

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42

Pal, Somnath. « Investigation of Dielectric and Magnetic Properties of Some Selected Transition Metal Oxide Systems ». Thesis, 2015. http://etd.iisc.ac.in/handle/2005/3878.

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High dielectric constant materials have tremendous impact on miniaturization of devices that are used in various applications like wireless communication systems, microelectronics, global positioning systems, etc. To store electric charge in a very small space necessarily needs a capacitor with very high dielectric constant. Thus, these materials are very important in fabricating capacitors, or metal oxide semiconductor filed effect transistor (MOSFET). Among the existing commercially available devices, silicon-based microelectronic devices are commonly used based on the moderately stable dielectric constants of silicon with low losses and minimal temperature and frequency dependence. However, now-a-days, the perovskite based transition metal oxides have drawn attention that have the ability to fulfill all the requirements for being a good dielectric material in all the industrial applications. In this thesis we have studied a few selected perovskite based transition metal oxide systems in terms of their dielectric and magnetic behaviour. In Chapter 1, we have have given brief introductions about the some application of dielectric materials and the origin of dielectric and magnetic properties in the materials. We have also discussed about the polarisation in the dielectric materials to understand it’s frequency dependence and also to formalise different relaxation behaviour with the help of physical and mathematical explanation. In Chapter 2, we describe the various methodologies adopted in this thesis. In Chapter 3, we have studied the dielectric behaviour of Nd2NiMnO6, a rare earth based double perovskite ferromagnetic insulator. We successfully synthesised and characterised the compounds, settled the valency issues with the help of temperature dependent XAS of the transition metal atom in contrast to the existing controversy available in literature. We have found that this material shows relaxor kind behaviour with a colossal dielectric constant value. We have studied in details the origin of the colossal dielectric constant and the relaxation behaviour along with the a.c and d.c. transport properties. We have shown the origin of the ferromagnetism (TC ∼ 200 K) with a low temperature antiferromagnetic ordering (TN ∼ 55 K) with the help of detailed studies of temperature dependent d.c., a.c. magnetism and their XMCD. We have also investigated the isothermal variation of magnetodielectric and magnetoresistance behaviour as a function of magnetic field and their origin. In Chapter 4,we study the effect of cation anti-site disorder on the magnetic, dielectric and transport properties of another rare earth based ferromagnetic double perovskite insulator La2NiMnO6 by controlling different extent of anti-site disordered. We have confirmed the valency of the transition metal cations using XAS technique and followed by shown, different types of magnetic interaction between the transition metal cations using d.c magnetic, quantitative XMCD analysis and the origin of large dielectric response, a.c. transport & dielectric relaxation using temperature variation dielectric measurement as an experimental evidence in contrast of our previous speculation published in literature. We further have studied, the coupling between the magnetic and electric spin through isothermal magnetodielectric measurement. In Chapter 5, we have successfully synthesised and characterised a solid solution of YMnxIn1−xO3 series via different mol % of In doping in the multiferroic YMnO3 system. YMnO3 is a well known multiferroic material studied rigorously during past few decades. We have seen, YMnO3 which has a antiferromagnetic ordering temperature of ∼ 75 K suppressed with increasing the dopant concentration In. We have figured out the effect of In doping in the suppression of multiferroic phase and extended it to the dielectric properties. We have found that, the temperature dependence of dielectric constant shows an anomaly at the magnetic ordering temperature and studied magnetodielectric coupling. We have also investigated the temperature variation of dielectric relaxation and a.c. transport behaviour as a function of composition. In Chapter 6, we have identified the phase seperation and proposed a phase diagram as function of Gd doping in the Ho2−xGdxCuTiO6 double perovskite, where two end member, namely Ho2CuTiO6 and Gd2CuTiO6 are found to be in two different crystallographic phase as, hexagonal (P63cm) and orthorhombic (Pnmm), respectively. We have characterised the valency of the transition metal cations using XAS.We have seen very less temperature and frequency dependence of dielectric constant in hexagonal phase in compare to the orthorhombic phase and tried to figuring out from experimental analysis by performing temperature dependence dielectric const measurement. We also have shown the effect of doping in the origin of dielectric relaxation, a.c transport and magnetic behaviour of this system. In Chapter 7, we have synthesised and characterised successfully two different rare earth based layered perovskite La3Cu2VO9 and La4Cu3MoO12 compounds are of centrosymmetric space group. We have figured it of the valency of the different atoms present in the compound using XAS. We also do have observed the good temperature stability of dielectric constant of these materials and explored origin of mechanism in the dielectric relaxation, a.c. transport property by performing the temperature dependance dielectric measurement. The magnetic structure also have shown with the help of d.d. magnetic measurements. In Appendix A, we have seen the very stable dielectric constant constant from very low to above room temperature of the 2D nano PbS. The frequency stability of dielectric constant is also remarkable in compare to bulk PbS values available in literature. We have explored the origin of the conductivity and relaxation mechanism performing dielectric constant measurement. In conclusion, we investigate, in this thesis, dielectric properties of different transition metal oxides system and the mechanism of dielectric relaxation, a.c, d.c transport and their origin of magnetic response.

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43

Pal, Somnath. « Investigation of Dielectric and Magnetic Properties of Some Selected Transition Metal Oxide Systems ». Thesis, 2015. http://etd.iisc.ernet.in/2005/3878.

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Résumé :

High dielectric constant materials have tremendous impact on miniaturization of devices that are used in various applications like wireless communication systems, microelectronics, global positioning systems, etc. To store electric charge in a very small space necessarily needs a capacitor with very high dielectric constant. Thus, these materials are very important in fabricating capacitors, or metal oxide semiconductor filed effect transistor (MOSFET). Among the existing commercially available devices, silicon-based microelectronic devices are commonly used based on the moderately stable dielectric constants of silicon with low losses and minimal temperature and frequency dependence. However, now-a-days, the perovskite based transition metal oxides have drawn attention that have the ability to fulfill all the requirements for being a good dielectric material in all the industrial applications. In this thesis we have studied a few selected perovskite based transition metal oxide systems in terms of their dielectric and magnetic behaviour. In Chapter 1, we have have given brief introductions about the some application of dielectric materials and the origin of dielectric and magnetic properties in the materials. We have also discussed about the polarisation in the dielectric materials to understand it’s frequency dependence and also to formalise different relaxation behaviour with the help of physical and mathematical explanation. In Chapter 2, we describe the various methodologies adopted in this thesis. In Chapter 3, we have studied the dielectric behaviour of Nd2NiMnO6, a rare earth based double perovskite ferromagnetic insulator. We successfully synthesised and characterised the compounds, settled the valency issues with the help of temperature dependent XAS of the transition metal atom in contrast to the existing controversy available in literature. We have found that this material shows relaxor kind behaviour with a colossal dielectric constant value. We have studied in details the origin of the colossal dielectric constant and the relaxation behaviour along with the a.c and d.c. transport properties. We have shown the origin of the ferromagnetism (TC ∼ 200 K) with a low temperature antiferromagnetic ordering (TN ∼ 55 K) with the help of detailed studies of temperature dependent d.c., a.c. magnetism and their XMCD. We have also investigated the isothermal variation of magnetodielectric and magnetoresistance behaviour as a function of magnetic field and their origin. In Chapter 4,we study the effect of cation anti-site disorder on the magnetic, dielectric and transport properties of another rare earth based ferromagnetic double perovskite insulator La2NiMnO6 by controlling different extent of anti-site disordered. We have confirmed the valency of the transition metal cations using XAS technique and followed by shown, different types of magnetic interaction between the transition metal cations using d.c magnetic, quantitative XMCD analysis and the origin of large dielectric response, a.c. transport & dielectric relaxation using temperature variation dielectric measurement as an experimental evidence in contrast of our previous speculation published in literature. We further have studied, the coupling between the magnetic and electric spin through isothermal magnetodielectric measurement. In Chapter 5, we have successfully synthesised and characterised a solid solution of YMnxIn1−xO3 series via different mol % of In doping in the multiferroic YMnO3 system. YMnO3 is a well known multiferroic material studied rigorously during past few decades. We have seen, YMnO3 which has a antiferromagnetic ordering temperature of ∼ 75 K suppressed with increasing the dopant concentration In. We have figured out the effect of In doping in the suppression of multiferroic phase and extended it to the dielectric properties. We have found that, the temperature dependence of dielectric constant shows an anomaly at the magnetic ordering temperature and studied magnetodielectric coupling. We have also investigated the temperature variation of dielectric relaxation and a.c. transport behaviour as a function of composition. In Chapter 6, we have identified the phase seperation and proposed a phase diagram as function of Gd doping in the Ho2−xGdxCuTiO6 double perovskite, where two end member, namely Ho2CuTiO6 and Gd2CuTiO6 are found to be in two different crystallographic phase as, hexagonal (P63cm) and orthorhombic (Pnmm), respectively. We have characterised the valency of the transition metal cations using XAS.We have seen very less temperature and frequency dependence of dielectric constant in hexagonal phase in compare to the orthorhombic phase and tried to figuring out from experimental analysis by performing temperature dependence dielectric const measurement. We also have shown the effect of doping in the origin of dielectric relaxation, a.c transport and magnetic behaviour of this system. In Chapter 7, we have synthesised and characterised successfully two different rare earth based layered perovskite La3Cu2VO9 and La4Cu3MoO12 compounds are of centrosymmetric space group. We have figured it of the valency of the different atoms present in the compound using XAS. We also do have observed the good temperature stability of dielectric constant of these materials and explored origin of mechanism in the dielectric relaxation, a.c. transport property by performing the temperature dependance dielectric measurement. The magnetic structure also have shown with the help of d.d. magnetic measurements. In Appendix A, we have seen the very stable dielectric constant constant from very low to above room temperature of the 2D nano PbS. The frequency stability of dielectric constant is also remarkable in compare to bulk PbS values available in literature. We have explored the origin of the conductivity and relaxation mechanism performing dielectric constant measurement. In conclusion, we investigate, in this thesis, dielectric properties of different transition metal oxides system and the mechanism of dielectric relaxation, a.c, d.c transport and their origin of magnetic response.

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林美如. « Optical properties of multiferroic oxides and sulfides ». Thesis, 2007. http://ndltd.ncl.edu.tw/handle/34507608505737032995.

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碩士
國立臺灣師範大學
物理學系
95
We study the optical properties of single crystalline multiferroic materials, such as (Tb1-xNax)MnO3 (x = 0.0, 0.03, and 0.05), DyMnO3, and CdCr2S4. The room-temperature Raman spectra of TbMnO3 are similar with the previous results of Phys. Rev. B 73, 064302 (2006). The position and intensity of Raman-active phonons are perturbed to some extent by Na doping. It is likely that monovalent Na+ ions were used to create oxygen vacancies and to induce the local lattice distortions. When doped with Dy on Tb, the phonon frequencies are hardening and their linewidths are narrowing, which is due to the chemical substitution of the smaller Dy ions into the bigger Tb ionic sites. The room-temperature Raman spectra of CdCr2S4 are also similar with the previous results of Phys. Rev. B 21, 1316 (1980). With decreasing temperature, overall infrared-active phonon spectra of (Tb1-xNax)MnO3 and DyMnO3 remain unchanged. However, the phonon mode at about 380 cm-1 show a softening and an increased intensity at low temperature, which is possibly due to the redistribution of effective charges in the unit cell. In the ferromagnetic phase below 84 K, the phonon peaks of CdCr2S4 near 325 and 381 cm-1 show a shift to lower frequencies, indicating the spin-phonon coupling via the superexchange interactions of Cr-S-Cr and Cr-S-Cd-S-Cr.

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Ghosh, Anirban. « Experimental And Theoretical Studies Of Strongly Correlated Multiferroic Oxides ». Thesis, 2010. https://etd.iisc.ac.in/handle/2005/1216.

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This thesis presents the synthesis and investigations of physical and chemical properties of multiferroic materials experimentally as well as theoretically. Multiferroics are materials in which at least two of the three ferroic orders, ferroelectricity, ferromagnetism and ferroelasticity occur in the same phase. Multiferroics, have the potential to be used as a four state as well as cross switchable memory devices. The thesis is organized into seven Chapters. Chapter 1 gives a brief overview of the different facets of multiferroics, explaining the origin of Multiferroicity and magnetoelectric coupling, their possible technological applications and the challenges involved. Chapter 2-4 concerns the experimental aspects and chapter 5-7 concerns the theoretical aspects. Chapter 2 deals with experimental investigations on nanoscale charge-ordered rare earth manganites. It shows with decreasing particle size the ferromagnetic interaction increases and the charge-ordering vanishes down to the lowest sizes. Chapter 3 describes magneto-dielectric, magnetic and ferroelectric properties of hexagonal LuMnO3. It also describes the Raman spectroscopy of this compound through the magnetic and ferroelectric transition temperatures. Chapter 4 deals with the anisotropic multiferroic properties in single crystals of hexagonal ErMnO3. In chapter 5 a brief introduction of density functional theory (DFT) is given. Chapter 6 deals with the magneto-structural changes, spin-phonon couplings and crystal field splittings for the different magnetic orderings LuMnO3. Chapter 7 elucidates the role of Lu d0-ness for the ferroelectricity observed of this compound.

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46

Ghosh, Anirban. « Experimental And Theoretical Studies Of Strongly Correlated Multiferroic Oxides ». Thesis, 2010. http://hdl.handle.net/2005/1216.

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This thesis presents the synthesis and investigations of physical and chemical properties of multiferroic materials experimentally as well as theoretically. Multiferroics are materials in which at least two of the three ferroic orders, ferroelectricity, ferromagnetism and ferroelasticity occur in the same phase. Multiferroics, have the potential to be used as a four state as well as cross switchable memory devices. The thesis is organized into seven Chapters. Chapter 1 gives a brief overview of the different facets of multiferroics, explaining the origin of Multiferroicity and magnetoelectric coupling, their possible technological applications and the challenges involved. Chapter 2-4 concerns the experimental aspects and chapter 5-7 concerns the theoretical aspects. Chapter 2 deals with experimental investigations on nanoscale charge-ordered rare earth manganites. It shows with decreasing particle size the ferromagnetic interaction increases and the charge-ordering vanishes down to the lowest sizes. Chapter 3 describes magneto-dielectric, magnetic and ferroelectric properties of hexagonal LuMnO3. It also describes the Raman spectroscopy of this compound through the magnetic and ferroelectric transition temperatures. Chapter 4 deals with the anisotropic multiferroic properties in single crystals of hexagonal ErMnO3. In chapter 5 a brief introduction of density functional theory (DFT) is given. Chapter 6 deals with the magneto-structural changes, spin-phonon couplings and crystal field splittings for the different magnetic orderings LuMnO3. Chapter 7 elucidates the role of Lu d0-ness for the ferroelectricity observed of this compound.

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Huang, Hung-Lung, et 黃鴻隆. « First-Principle Studies of Physical Properties of HeuslerAlloys and Multiferroic Oxides ». Thesis, 2015. http://ndltd.ncl.edu.tw/handle/20986757779148014188.

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博士
國立臺灣大學
物理研究所
103
We perform a systematic ab initio study of two principal spin-related phenomena,namely, anomalous Hall effect and current spin polarization, in Co2Fe-based Heusler compounds Co2FeX (X = Al, Ga, In, Si, Ge, Sn) in the cubic L21 structure. First, we find that the spin-polarization of the longitudinal current (PL) in Co2FeX (X = Al, Ga, In, Al0.5Si0.5 and Sn) approximately equals to 100 % The other compounds also have a high current spin polarization with PL larger than 85%. Interestingly, PD is negative in Co2FeX (X = Si, Ge and Sn), differing in sign from the PL as well as that from the results of transport experiments. Second, the calculated anomalous Hall conductivities (AHCs) are moderate, being within 200 S/cm, and agree well with the results of experiments on highly L21 ordered Co2FeSi specimen. Third, the calculated total magnetic moments are consistent with the corresponding experimental ones in all the studied compounds except Co2FeSi. We also performed the GGA plus on-site Coulomb interaction U calculations. We found that including the U affects the calculated total magnetic moment, spin polarization and AHC significantly. Meanwhile, unfortunately, this results in a disagreement with the available experimental results. All these interesting findings are discussed in terms of the underlying band structures. We also study the physical mechanism for ferroelectric polarization of multiferroic oxide, such as BiMnO3 and Li(Na)Cu2O2 with C2/c and Pnma structures. We found that the ground state of magnetic structure of BiMnO3 is noncollinear, the x- and z-directions are antiferromagnetic, the y-direction is ferromagnetic. The net magnetic dipole moment is 3.98 μB per chemical formula and it is consistent with experiment results. We also performed the electric polarized calculations using Berry phase method. The findings indicate that there is significant electric-polarization at both antiferromagnetism (AF2) and ferrimagnetism (Fe2), but there is no electricpolarization at the ground state of FM. This interesting phenomenon comes from the breaking of the spacial inversion symmetry. The magnitude of electric polarization is related strongly with the magnitude of antiferromagnetic moment. We also perform the GGA+U method to study both LiCu2O2 and NaCu2O2. Their structures are very similar, Therefore, both compounds exhibit almost identical physical properties, such as electronic structure, magnetism and ferroelectricity. However, experimental results show that LiCu2O2 is multiferroic, but NaCu2O2 is not. Antiferroelectricity in NaCu2O2 could be explained by multiple spin-spiral CuO ribbons along the y-axis with opposite chiralities. However, this would leave the ferroelectricity in LiCu2O2 unexplained. Interdiffusion of Li and Cu in LiCu2O2 while no interdiffusion of Na and Cu in NaCu2O2 could be a resolution. However, the good agreement in electronic structure between the XAS measurement and GGA+U calculation suggest that this is unlikely the explanation. We have carried out a systematic ab initio study of the magnetic properties of Heusler compounds and multiferroic oxide. These findings suggest that our simulation results are consistent with that of experiments. We hope that our systematic studies can help to understand the microscopic mechanism and have some benefits to the development of related applications.

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Denyszyn, Jonathan Charles. « The dielectric behavior of perovskite-related manganese oxides with stretched bonds or multiferroic properties ». Thesis, 2006. http://hdl.handle.net/2152/2859.

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49

Yan, Wei-De, et 顏維德. « Cobalt-Doping Effects on Photovoltaic and Structural Properties in BiFeO3 Multiferroic Ceramics ». Thesis, 2014. http://ndltd.ncl.edu.tw/handle/86161909726900075810.

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碩士
輔仁大學
物理學系碩士班
102
In this research, 5% and 10% Co-doped BFO multiferroic ceramics have been synthesized by solid state reaction (SSR) method with various sintering temperature and present single phase in XRD measurements. The average grain size of Co-doped BFO observed by SEM grows significantly as increasing sintering temperature. The ferromagnetic behavior at room temperature is enhanced as cobalt doped in BFO and grains demonstrate more rectangle shape with increasing Co content. The temperature- and frequency- dependent dielectric permittivity of Co-doped BFO show strong frequency dispersion and high electric conductivity around 250 oC. For photovoltaic (PV) effects measurement, the ITO and Au films were deposited on both sides of Co-doped BFO and the thickness of BFO is 0.2 mm. The diode laser of λ = 405 nm was used as an excitation source to measure open circuit voltage and short circuit current density. The photovoltaic phenomena can be explained by the developed model which is based on p-n junction concepts. On the other hand, the photovoltaic responses also depend on the average grain size and an application of magnetic field~3000 Oe. The relation between photovoltaic response and light intensity can be described by exponential equations Voc = Vb[1-exp(I/α)] and Jsc = Jb [1-exp(I/β)], where Voc, Jsc, Vb, and Jb are open-circuit voltage, short- circuit current density , saturated open-circuit voltage, and saturated short-circuit current density, respectively.

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Shen, Tsung-Wei, et 沈宗緯. « First-principles study in structural and elec-tronic properties of FeBaTiO3Fe multiferroic tunneling junction ». Thesis, 2019. http://ndltd.ncl.edu.tw/handle/jjm6yr.

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碩士
國立中央大學
物理學系
107
Multiferroic tunnel junction (MFTJs) is the combination of ferromag-netic (FM) and ferroelectric (FE) material system. To push for low energy consumption memory and logical spintronic devices, a reversal of magnet-ization requiring only the application of an electric field can be achieved via a ferroelectric (FE) barrier as an active role in a magnetic tunnelling junction. In this study, the first-principle calculation is employed to inves-tigate the atomic structure and electronic properties of (Fe2)7-(BaTiO3)m-(Fe2)6 superlattice with m=4, 6, 8. To better understand the magnetoelectric coupling between the magnetic moment of Fe electrode and the electric dipole moment of central ferroelectric BaTiO3 barrier, which is decided the direction of electric dipole (Δz

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