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Waterfield, Price Noah. "Domains and functionality in multiferroic BiFeO3 films". Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:e8a8f8ff-8510-4fdf-93f4-0037cebc0210.
Pełny tekst źródłaMasteghin, João Francisco Vieira. "Síntese e propriedades de filmes finos multiferróicos de BiFeO3". Universidade Estadual Paulista (UNESP), 2018. http://hdl.handle.net/11449/153560.
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Foram preparados filmes finos, de Ferrita de Bismuto (BiFeO3), considerado um dos principais multiferróico que são classes de materiais que apresentam ferroeletricidade e ferromagnetismo simultaneamente. Os filmes foram preparados por um rota química chamada de Sol-gel modificado, variando-se a quantidade de % de mol do Bismuto, depositados em substratos de platina Pt/TiO2/SiO2/Si(100), variando-se a temperatura de cristalização entre 400°C a 600°C, com o objetivo de eliminar algumas fases indesejadas encontradas na literatura. Alguns filmes finos passaram pelo tratamento térmico em atmosférica de O2, com o intuito de diminuir a condutividade, causada pelas vacâncias de oxigênio no material. Pelos resultados obtidos foi possível conseguir filmes finos sem as fases indesejadas e com condutividade não tão alta, sendo possível realizar análises elétricas. Assim, tornou-se possível analisar o comportamento da permissividade, impedância e condutividade em função do campo aplicado e da temperatura. Com tais resultados mostra-se a indicação de polarização iônica nestes filmes. Eles apresentam uma energia de ativação parecida com filme finos encontrados na literatura. Além disso, também mostra que o comportamento das propriedades físicas são os mesmos quando varia a temperatura e o campo.
Bismuth Ferrite (BiFeO3) thin films were prepared, considered one of the main multiferroic that are classes of materials that present ferroelectricity and ferromagnetism simultaneously. The films were prepared by a chemical path called modified sol-gel, varying the amount of Bismuth mol percentage, deposited on Pt/TiO2/SiO2/Si(100) platinum substrates, varying the crystallization temperature between 400 °C to 600 °C, with the aim of eliminating some unwanted phases found in literature. Some thin films underwent the thermal treatment in atmospheric O2, in order to reduce the conductivity, caused by the oxygen vacancies in the material. By the results obtained, it was possible to obtain thin films without the undesired phases and with not so high conductivity, being possible to perform electrical analysis. This way it was possible to analyze the behavior of the permissiveness, impedance and conductivity in function of the applied field and temperature. With these results, it is shown an indication of ionic polarization in these films. They have an activation energy similar to thin films found in literature. It is also shown that the behavior of the physical properties are the same when temperature and the field change.
González, Vázquez Otto E. "First-principles investigation of BiFeO3 and related multiferroic materials". Doctoral thesis, Universitat Autònoma de Barcelona, 2012. http://hdl.handle.net/10803/96248.
Pełny tekst źródłaThis work is about magnetoeltric multiferroics, a relatively new class of ma- terials discovered by the mid of the past century, which involve simultaneously ferroelectricity and magnetism. Perovskite oxide BiFeO3 (BFO) is one of the few multiferroic materials at room temperature. However, as its ferroelectric and anti- ferromagnetic transition temperatures are relatively high (about 1100 K and 640 K, respectively), BFO's electromechanical and magnetoelectric responses are small at ambient conditions. In this thesis we used ab-initio methods, based on density functional theory, to study the basic properties of BFO and proposed possible strategies for enhancing its response. We used rst-principles methods to perform a systematic search for potentially stable phases of BFO. We considered the distortions that are most common among perovskite oxides and found a large number of local minima of the energy. We discussed the variety of low-symmetry structures discovered, as well as the implications of these ndings as regards current experimental work on this compound. We also carried out a study of the Bi1�xLaxFeO3 (BLFO) solid solution formed by multiferroic BFO and the paraelectric antiferromagnet LaFeO3 (LFO). We dis- cussed the structural transformations that BLFO undergoes as a function of La content and the connection of our results with the existing crystallographic stud- ies. We found that, in a wide range of intermediate compositions, BLFO presents competitive phases that are essentially degenerate in energy. Further, our results suggested that, within this unusual morphotropic region, an electric eld might be used to induce various types of paraelectric-to-ferroelectric transitions in the compound. We also discussed BLFO's response properties and showed that they can be signi cantly enhanced by partial substitution of Bi/La atoms in the pure BFO and LFO materials. We analyzed the atomistic mechanisms responsible for such improved properties and showed that the e ects can be captured by simple phenomenological models that treat explicitly the composition x in a Landau-like potential. Furthermore, we performed a rst-principles study of BFO at high pressures. Our work revealed the main structural change in Bi's coordination and suppression of the ferroelectric distortion, electronic spin crossover and metallization, and mag- netic loss of order e ects favored by compression and how they are connected. Our results are consistent with and explain the striking manifold transitions observed experimentally We conclude our thesis presenting the preliminary results of an ongoing project in which we are modeling the energetics of the oxygen octahedra rotations in per- ovskite oxides. The model is tted to the rst-principles results and a careful check of its validity is carried out.
Blouzon, Camille. "Photoelectric and magnetic properties of multiferroic domain walls in BiFeO3". Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066006/document.
Pełny tekst źródłaAmong all multiferroics, BiFeO3 is a material of choice because its two ordering temperatures are well above 300K. It is a ferroelectric antiferromagnet, and magnetoelectric coupling has been demonstrated in bulk and in thin films. Remarkably, BiFeO3 has the largest polarization of all known ferroelectrics (100µC/cm²). A huge research effort is carried out worldwide to understand and exploit the physical properties of this material which requires to design and tailor BiFeO3 on many scales. In this sense, developing methods and tools to control the domain structure is essential to explore new emergent phenomena arising at domain walls. This is the aim of the present PhD work. Some of the original properties of BiFeO3 have been investigated including its photoelectric and magnetic properties. A particular attention is given to characterize in a parallel fashion bulk properties and domain walls properties, using original techniques of characterization such as Scanning Photocurrent Microscopy (SPCM), scattering synchrotron facilities or high field pulses. SPCM mapping reveals that depolarizing fields in the vicinity of a 180° domain wall can significantly improve the photovoltaic efficiency. Thus domain walls can be generated and precisely positioned in order to tailor the local photovoltaic efficiency. Moreover, X-ray resonant magnetic scattering on thin films with periodic domain structure shows that domain walls generate specific magnetic structures with possible uncompensated magnetization
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.
Pełny tekst źródłaWójcik, Katarzyna. "The synthesis, structure and reactivity of iron-bismuth complexes : Potential Molecular Precursors for Multiferroic BiFeO3". Doctoral thesis, Universitätsbibliothek Chemnitz, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-201000715.
Pełny tekst źródłaLorenz, Michael, Gerald Wagner, Vera Lazenka, Peter Schwinkendorf, Hiwa Modarresi, Bael Margriet J. Van, André Vantomme, Kristiaan Temst, Oliver Oeckler i Marius Grundmann. "Correlation of magnetoelectric coupling in multiferroic BaTiO3-BiFeO3 superlattices with oxygen vacancies and antiphase octahedral rotations". American Institute of Physics, 2015. https://ul.qucosa.de/id/qucosa%3A31214.
Pełny tekst źródłaYousfi, Said. "Mécanismes de conduction et effet photovoltaïque dans des films minces de BiFeO3". Electronic Thesis or Diss., Amiens, 2018. http://www.theses.fr/2018AMIE0017.
Pełny tekst źródłaThe multiferroic BiFeO3 is one of the most studied material because of the room temperature coexisting ferroelectric and antiferromagnetic state. It also shows a photovoltaic response not yet understood. The main objective of this thesis is therefore to investigate the the photovoltaic properties of epitaxial BiFeO3 thin films. Preliminary to photovoltaic studies an investigation of the conduction mechanism has been performed. A polaronic transport with next nearest hopping mechanism is evidenced with a change of regime below 253K. Below 253K variable range hopping transport is observed and involves defects states near the Fermi level. This transport behavior seems connected to the photovoltaic response and change observed at 253K in the photo-induced voltage. Interestingly the photovoltaic response is induced by the ferroelectric state and we demonstrate a switchable photovoltaic effect by an applied electric field. In order to artificially reproduce the domain structure involved in the photovoltaic effect in BiFeO3 BiFeO3/SrRuO3 superlattices have been fabricated and a preliminary structural investigation is presented. A structural change is evidenced from a rhombohedral structure to pseudo-tetragonal state in the superlattices with variable periodicities and we attribute this transition to the influence of the induced in-plane elastic strain
Jarrier, Romain. "Influence de la stœchiométrie sur les propriétés physiques du multiferroïque BiFeO3". Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00676879.
Pełny tekst źródłaKavanagh, Christopher M. "Synthesis and structure-property relationships in rare earth doped bismuth ferrite". Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/3555.
Pełny tekst źródłaAppert, Florian. "Conception et réalisation de détecteurs dédiés à l'analyse de couches minces par spectrométrie Mossbauer : application à l'étude des propriétés magnétiques de films d'oxydes multiferroïques". Thesis, Normandie, 2017. http://www.theses.fr/2017NORMR133/document.
Pełny tekst źródłaThis work is devoted to the development of two Mössbauer detectors dedicated to thin films studies by conversion electron Mössbauer spectrometry (CEMS), and to their use for the characterization of bismuth ferrite BiFeO3 (BFO) epitaxials thin films. The first designed instrument is composed of a proportional counter and a thermoelectric module. It allows CEMS acquisitions of Mössbauer spectra from 245 to 375K with an external magnetic field upto 1.4 T. The second device is based on a commercial channeltron™ and a continuous flow cryostat allowing measurements downto 4 K. The CEMS measurements have been performed on (110) and (001) oriented BFO layers with various thickness deposited on LaAlO3 et SrTiO3 substrates. Beyond a critical thickness, the (110) BFO exhibits a mixing of collinear and cycloidal magnetic phases. The collinear phase shows an anisotropy axis [001] direction which is located in the sample plane. The cycloid propagation plane have been found to be perpendicular to the sample plane. Both epitaxial strain and size effects have been proposed to explain the cycloid destabilization in the thinner films. In (001) BFO thin films, exhibiting a BFO tetragonal phase, the CEMS measurements have shown that the magnetic ordering temperature tends to decrease with the layer thickness
Curvello, Marcio Sena. "Síntese e caracterização de óxidos multiferroicos". reponame:Repositório Institucional da UFABC, 2017.
Znajdź pełny tekst źródłaTese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, Santo André, 2017.
Neste trabalho foram estudados os efeitos da substituição do Bi por um elemento terra-rara (R = Pr, Dy) e da adição de polímeros nas propriedades físicas de compostos de BiFeO3 (BFO) sintetizados pelo método hidrotermal assistido por micro-ondas. Inicialmente, amostras de BFO foram preparadas em diferentes condições de síntese (tempo, temperatura e concentração de KOH) e com este estudo escolheu-se os parâmetros de síntese utilizados neste trabalho para síntese de todas as amostras. As sínteses hidrotermais foram realizadas a 200 °C por 120 min com concentração de KOH de 4 M. Os compostos preparados foram avaliados por meio de medidas de difração de raios X (DRX) e de imagens de microscopia eletrônica de varredura (MEV). Na segunda etapa, o efeito da substituição de bismuto (Bi) por praseodímio (Pr) ou disprósio (Dy) foi investigado por meio de medidas das propriedades físicas caracterizadas por medidas de DRX e análise pelo método de refinamento de Rietveld, imagens de MEV, espec-tros de absorção na região UV-Vis, medidas de constante dielétrica em função da frequência e medidas de magnetização em função do campo magnético aplicado (MxH) e da temperatura (MxT). Por meio das análises de DRX das amostras de Bi1-xRxFeO3, foi observado que com a substituição de Bi por R as amostras tendem a cristalizar-se de forma polimórfica, apresentando duas simetrias: uma romboédrica (R3c) e outra monoclínica (Cc), sendo que a proporção da simetria monoclínica tende a aumentar com o aumento de x. Este polimorfismo, em geral, está associado a presença de Fe2+ na estrutura do Bi1-xRxFeO3, que exerce forte influência nas pro-priedades magnéticas destes compostos. As medidas elétricas mostraram uma melhora dos va-lores da constante dielétrica destas amostras quando comparadas a amostras sem substituição e com resultados listados na literatura para compostos BiFeO3 dopados preparados por outras metodologias. Resultados de absorção na região UV-Vis dos compostos Bi1-xRxFeO3 eviden-ciam uma diminuição do gap de energia de 2,1 eV para a amostra com x = 0 a 1,7eV para com x = 0,3 (Pr). Por fim, no estudo do efeito da adição de polímeros ou surfactantes, foram adici-onados os seguintes materiais: polietilenoglicol (PEG), polivinilpirrolidona (PVP), carboxime-tilcelulose de sódio (NaCMC) ou brometo de cetiltrimetilamonio (CTAB) com o objetivo de verificar a influência de diferentes morfologias nas propriedades físicas do BFO. De fato, o surfactante na síntese do BiFeO3 modificou a morfologia destes compostos, sendo que o resul-tado diferencial foi a obtenção do BiFeO3 na forma de nanobastões utilizando o CTAB. Os demais surfactantes apresentaram formatos similares aqueles já descritos na literatura. As me-didas de UV-Vis revelaram que o valor do gap de energia variou de 1,7 a 2,1 eV com a variação da morfologia do BFO, sendo que este resultado já foi observado em compostos de BFO com diferentes morfologias na literatura. As medidas de constante dielétrica em função da frequên-cia apresentaram um comportamento similar àqueles observados para o BFO preparado sem surfactante. As caracterizações magnéticas revelaram modificações nas curvas de MxT e MxH na região de baixa temperatura (<50 K), o que foi atribuído a presença de fases adicionais nestas amostras.
In this work, the effects of chemical substitution and addition of polymers on the physical prop-erties of BiFeO3 (BFO) compounds synthesized by microwave-assisted hydrothermal method were studied. Firstly, samples of BFO were prepared using different synthesis conditions (time, temperature, KOH concentration), with this study we chose the synthesis parameters used in this work to produce all samples. In order to obtain the parameters that allow the production of compounds with the desired crystalline phase. Hydrothermal syntheses were performed at 200°C during 120 min with KOH concentration of 4M. The compounds were evaluated by X-ray diffraction (XRD) measurements and images of Scanning Electronic Microscopy (SEM). In the second step, the effect of bismuth (Bi) substitution by praseodymium (Pr) or dysprosium (Dy) was investigated by measurements of the physical properties characterized by XRD meas-urements, and analysis by the Rietveld method of refinement, SEM images, absorption spectra in the UV-Vis region, dielectric constant measurements as a function of frequency, and mag-netization measurements as a function of the applied magnetic field (MxH) and temperature (MxT). By means of the XRD analysis of Bi1-xRxFeO3 samples, it was observed that with Bi for R substitution these samples are likely to crystallize in a polymorphic way, which present a rhomboedric (R3c) and a monoclinic (Cc) symmetry. The proportion of monoclinic symmetry tends to increase with the increasing of x. In general, such polymorphism is related to the Fe2+ content in the Bi1-xRxFeO3 structure, which provides a strong influence in the magnetic proper-ties of these compounds. Electrical measurements of the samples show dielectric constants val-ues similar to values observed for undopped and dopped-BiFeO3 prepared by other methodologies. UV-vis absorption results of Bi1-xRxFeO3 compounds revealed a decrease of energy gap from 2.1 eV for sample with x =0 to 1.7 eV for x = 0.3 (Pr). Finally, study of the effect of polymers or surfactants addition, the following materials were added: polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), sodium carboxymethylcellulose (NaCMC) or cetyltrimethylammonium bromide (CTAB) to verify the influence of different morphologies on the physical properties of BFO. In fact, the morphology of BFO was modified through the sur-factant addition, the most remarkable results is the nanostick shape observed for BFO samples prepared with CTAB. Samples prepared using the other surfactants revealed different mor-phology than those reported in literature. UV-vis measurements revealed energy gap varying from 1.7 to 2.1 eV for BFO samples with different morphologies. Dielectric constant measure-ments as function of frequency presents similar behavior than those observed for BFO without surfactant. Magnetic characterizations revealed changes in low temperature region (<50 K), which is attributed to the presence of additional phases in these samples.
Jahjah, Walaa. "NanOstructures MultIferroïques INtrinsèques et extrinsèques : vers un contrôle Électrique des propriétés magnétiquEs (NOMINÉE) Influence of mesoporous or parasitic BiFeO3 structural state on the magnetization reversal in multiferroic BiFeO3/Ni81Fe19polycrystalline bilayers, in Journal of Applied Physics 124 (23), December 2018 Spin pumping as a generic probe for linear spin fluctuations: demonstration with ferromagnetic and antiferromagnetic orders, metallic and insulating electrical states, in Applied Physics Express 12(2), January 2019 Thickness dependence of magnetization reversal and magnetostriction in Fe81Ga19 thin films, in Physical Review Applied 12, August 2019". Thesis, Brest, 2019. http://www.theses.fr/2019BRES0070.
Pełny tekst źródłaWe conducted three experimental studies of magnetization reversal (MR) behavior in three different types of bilayers, under different types of strain. We studied the influence on the magnetic properties of the structural state in the BiFe03, of magnetoelastic mechanical strain in the Fe81Ga19, which we then coupled to electrical and even thermal strainA bilayer consisted of using a ferromagnetic Ni81Fe19, and an intrinsic multiferroic BiFe03. These polycrystalline thin films are deposited by sputtering. Their structure and morphology are characterized by X-ray diffraction, and transmission electron microscopy, revealing two fundamentally different structural states of the BiFeO3 due to defects. The MR is analyzed by vibrating sample vector magnetometry, providing angular measurements it room temperature. The parasitic state with the parasitic phase Bi2O3 increases the values of the exchange field according to its concentration, which we can control. A mesoporous state is also highlighted, and prevents the establishment of the unidirectional anisotropy.Magnetostrictive thin films of Fe81Ga19 are deposited on glass substrates. Their characterizations reveal thicknessdependent magnetic properties, in correspondence with the structural state. Two remarkable crystallographic directions for the whole range of thicknesses allow a coherent MR. The thinner films have a magnetostriction coefficient value of 20 ppm, which decreases for the thicker films. This trend is associated with a predominant surface texture which is reduced in favor of the polycrystalline volume with non-preferential orientation.Such Fe81Ga19 films are deposited on single-cristalline ferroelectric substrates of PMN-PZT to form an extrinsic multiferroic.The MR and the anisotropy character are controlled by an electric field. The composite reveals a strong inverse magnetoelectric coupling αCME between the two piezoelectric and magnetostrictive phases, of value among the best reported so far. Measurements at low temperatures show a magnetomechanical effect due to thermal stress, and imposed by the nature of the substrate
Wang, Junling. "Deposition and characterization of multiferroic BiFeO₃ thin films". College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/2188.
Pełny tekst źródłaThesis research directed by: Material Science and Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
Bai, Xiaofei. "Effet de taille et du dopage sur la structure, les transitions et les propriétés optiques de particules du multiferroïque BiFeO₃ pour des applications photocatalytiques". Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLC013/document.
Pełny tekst źródłaThis experimental PhD work has been dedicated to the synthesis, by wet chemistry methods, and characterization of nanoparticles based on multiferroic BiFeO3, with the aim of using them for photocatalytic applications. This material presents a bandgap of 2.6eV, which allows the charge carrier photoexcitation in the visible range, making BiFeO3 a very interesting system for photoinduced processes. This thesis has been particularly focused on characterizing the properties of BiFeO3 nanoparticles in view of understanding the relationship of their properties on their potential use for photocatalytic applications. First of all, the topic of the size effect on the structural properties, phase transitions, and physics and chemistry of the particles has been developed, keeping as first aim to separate the properties related to the surface from those arising from the bulk/core of the particle. To do so, the mastering and optimization of the synthesis processes of BiFeO3 particles at the nano and microscale were needed, to finally obtain different size compounds with high crystalline quality. Despite the size reduction of the particles, we notice that, thanks to the control of the synthesis process, our BiFeO3 nanoparticles present properties very close to those of the bulk BiFeO3 material, keeping the rhombohedral structure R3c with weak strain effects. In order to indirectly tune the optical properties exploiting the doping, we have succeeded in realizing a homogenous La3+ doping, and a partial Ca2+ doping, on the Bi3+ site. The optical properties of the nanoparticles and their use on the first photocatalytic experiments for degrading rhodamine B dye have shown the complexity of the physics and chemistry phenomena at their surface and of the light-particle processes. After analyzing optical absorbance data as a function of the particle size, we observe that the deduced bandgap for different particles is not the main parameter directing the photocatalytic performances. Other factors have been identified to be at the origin of the localization of the photoexcited charges, as the surface states linked to the skin layer of the nanoparticles, depicting structural defects, a reduction of the oxidation state of Fe3+ towards Fe2+ and the stabilization of other adsorbates, such as FeOOH; all these parameters may contribute to the change on the photocatalytic performances. The photocatalytic results are very encouraging, motivating to continue the study of BiFeO3 based nanoparticles, though depicting a 50% rhodamine B degradation after 4h of photocatalytic reaction using some of the present nanoparticles
Lazenka, Vera, Johanna K. Jochum, Michael Lorenz, Hiwa Modarresi, Haraldur P. Gunnlaugsson, Marius Grundmann, Bael Margriet J. Van, Kristiaan Temst i André Vantomme. "Interface induced out-of-plane magnetic anisotropy in magnetoelectric BiFeO3-BaTiO3 superlattices". American Institute of Physics, 2017. https://ul.qucosa.de/id/qucosa%3A31216.
Pełny tekst źródłaFischer, Johanna. "Imaging and tailoring electric and antiferromagnetic textures in multiferroic thin films of BiFeO₃". Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASP013.
Pełny tekst źródłaAntiferromagnetic materials are generating a growing interest for spintronics due to important assets such as their insensitivity to spurious magnetic fields and fast magnetization dynamics. A major bottleneck for functional devices is the readout and electric control of the antiferromagnetic order. In multiferroics, the magnetoelectric coupling between ferroelectric and antiferromagnetic orders may represent an efficient way to control antiferromagnetism with an electric field. In this thesis, we observe a wide variety of antiferromagnetic textures that we control by strain engineering and electric field in the archetypical multiferroic, BiFeO₃. We elaborate epitaxial BiFeO₃ thin films, harbouring various ferroelectric domain landscapes, as imaged by piezoresponse force microscopy. Furthermore, we resort on an inverse phase transition to improve the global electrical order from maze to perfect array of striped ferroelectric domains. Using scanning NV magnetometry, we correlate the antiferromagnetic landscapes to the ferroelectric ones. We demonstrate that strain stabilizes bulk or exotic spin cycloids, as well as collinear antiferromagnetic order. With resonant X-ray elastic scattering, we macroscopically confirm the existence of two types of cycloid. Furthermore, we electrically design antiferromagnetic landscapes on demand, changing one type of cycloid to another or turning collinear states into non-collinear ones. Finally, resorting on anisotropic strain, we stabilize a single domain ferroelectric state, in which a single spin cycloid propagates. This opens a fantastic avenue to investigate the coupling between non-collinear antiferromagnetism and spin transport
Dupe, Bertrand. "Propriétés structurales et diélectrique de BiFe03 en couche mince". Phd thesis, Ecole Centrale Paris, 2010. http://tel.archives-ouvertes.fr/tel-00646714.
Pełny tekst źródłaBruyer, Emilie. "Propriétés structurales, électroniques et ferroélectriques de systèmes Ln₂Ti₂O₇ (Ln=lanthanides) et d'hétérostructures SrTiO₃ / BiFeO₃". Thesis, Artois, 2012. http://www.theses.fr/2012ARTO0401/document.
Pełny tekst źródłaIn this work, first-principles calculations and experimental measurements have been done in order to investiguate the structural, electroniq and ferroelectric properties of Ln2Ti2O7 (Ln = La, Nd, Sm, Gd) and BiFeO3 oxydes. Calculations on La2Ti2O7 and Nd2Ti2O7 confirmed their ferroelectricity. Other oxydes belonging to the Ln2Ti2O7 family have also been investigated. The results showed an enhancement of the spontaneous polarization within these compounds compared to that of La2Ti2O7 and Nd2Ti2O7. The second part of this work is related to the structural and ferroelectric properties of bismuth ferrite BiFeO3. The evolution of its properties when undergoing an epitaxial strain have been investigated by ab initio calculations and piezoresponse force microscopy measurements on thin films deposited on a (001)-SrTiO3 substrate. Our results showed a modification of the inner structure of BiFeO3 under stain, leading to a continuous reorientation of the spontaneous polarization vector towards [001]. The third part of our study consists in the computational design and synthesis of (SrTiO3)n(BiFeO3)m superlattices. Our calculations showed that epitaxial strain imposed to the superlattice brings a further control of physical properties of BiFeO3 as compared with its behaviour when deposited alone in a thin film. PFM analysis showed a decrease of the coercive field for STO/LNO/(STO)n(BFO)m superlattices as compared with those measured on STO/BFO bi-layers and on BiFeO3 thin films
Wu, Shan-Lin, i 吳尚霖. "Transport properties of multiferroic BiFeO3 transistors". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/10807390970679908413.
Pełny tekst źródłaYang, wei-chun, i 楊偉群. "A-site ion substitution effectin multiferroic BiFeO3 ceramics". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/23922101744104176585.
Pełny tekst źródła輔仁大學
物理學系
99
This work is to investigate the structural, electrical, and magnetic properties of various A-site ion substations in BiFeO3. The samples were fabricated by the solid state reaction method (SSR). The experiment methods include the high-resolution synchrotron XRD, dielectric constant, SEM(grain size), and magnetic properties. The (Bi0.95La0.05)FeO3 and (Bi0.95Nd0.05)FeO3 ceramics exhibit a rhombohedral-orthorhombic-cubic phase transition. The dielectric permittivities of (Bi0.95La0.05)FeO3 and (Bi0.95Nd0.05)FeO3 ceramics are 71.045 and 74.937 at room temperature, respectively. The dielectric loss of (Bi0.95La0.05)FeO3 and (Bi0.95La0.05)FeO3 are about 0.0127 and 0.1415 at room temperature, respectively. The frequency dependent dielectric maximum in 600~800 K is likely activated by the antiferromagnetic transition which takes place at the Néel temperature (TN). This phenomenon associates with a local minimum in rhombohedral distortion angle αR near TN.
Lin, Qi-Rui, i 林其叡. "Domain structures and growth in multiferroic BiFeO3 films". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/08632874787624615705.
Pełny tekst źródła國立成功大學
物理學系碩博士班
96
In this study, I observe the domain structure and growth at nanoscale by the piezoresponse force microscopy (PFM) in the multiferroic BiFeO3 thin films. The topography, in-plane (IP) and out-of-plane (OP) components of domains for BFO thin films can be revealed simultaneously. The effects of free carriers exist at grain boundaries, where free carries are assumed to screen the depolarization fields in rough epitaxial and polycrystalline samples. The effect of free carriers also provide the explanations for that BFO ferroelectric domains are usually larger than theory expected. The stripe-like domains formed as normal states by considering ferroelectric ordering, magnetoelectric coupling, and the depolarization energy. When applying lower voltage pulses, the domain grows logarithmically with time, which suggests the observed domain wall follows the creep motion in (111) epitaxial sample. When applying higher voltage pulses (close to the macroscopically saturation voltage), the observed states are in equilibrium so that the domain size is determined by minimizing the domain free energies, which include the contributions from (1) the depolarization energy from the bound charges on the domain wall; (2) the surface energy of the domain wall and (3) interaction energy between the domain and the tip fields. The threshold electric field of nonequlibrium creep wall for negative bias (~0.81-0.91 MV/cm) is smaller than that (~1.71-1.93 MV/cm) for positive bias. It is reasonable since the original polarizations of the films tend to direct toward the bottom electrodes.
Chiang, Ming Ta, i 江明達. "Synthesis and Photovoltaic Effects of Multiferroic BiFeO3 Ceramics". Thesis, 2014. http://ndltd.ncl.edu.tw/handle/61967416017836242394.
Pełny tekst źródła輔仁大學
物理學系碩士班
101
In this thesis, the synthesizing process of BiFeO3 (BFO) polycrystalline multiferroic ceramic by solid-state reaction method has been explained systematically. The as prepared BFO ceramic sample shows high purity single phase without any traces of secondary phases. In order to study the photovoltaic effect, ITO/BFO/Au heterostructure (with electrodes of Indium tin oxide and Au films) has been prepared. Photovoltaic responses under near-ultraviolet illumination at λ= 405 nm exhibit nonlinear dependence on light intensity, whereas light illumination at λ = 532 nm does not show any significant response due to its energy band gap of about 2.7 eV. Under the illumination at λ= 405 nm, the measured photovoltage, and photovoltaic current density are 0.83V and 0.25 A/m2 respectively for a chosen sample thickness of 0.2 mm. The maximal power conversion efficiency is about 0.0289% at illumination intensity of 9.2 W/m2. It is also verified that the photovoltaic responses increases as the sample thickness decreases and it can be enhanced after dc E-field poling. A model based on the PN junction theory has been proposed in order to explain the photovoltaic effects. The model gives good agreement between the theoretical and experimental values.
Tu, Hao-Chun, i 杜浩群. "Photo-Induced Electric Effects on Multiferroic BiFeO3 Ceramics". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/85686199937337909875.
Pełny tekst źródła輔仁大學
物理學系
100
This study used the solid state reaction to produce BiFeO3 multiferroic ceramics. The processes include mixing powders, ball milling, calcining, high -energy ball milling, granulation, pressing, and sintering. XRD of BiFeO3 ceramics show high purity without obvious second phases. Room -temperature dielectric permittivity is about 48 (for f=1 MHz). The maximum dielectric-permittivities occur between 650-800 K and show obvious frequency-dependent dispersion. Dielectric loss increases rapidly when temperature is above 630 K because of the thermal-active conductivity. In one-dimension barrier model, a turning point of conductivity appears around 610 K, which is close to the Nèel temperature. The maximum of dielectric permittivity from the barrier model is consistent with the experiment data. Probably, the main reason is due to transition from antiferromagnetism to paramagnetism. Comparing with two different diode lasers, the photovoltaic responses of 373 nm laser is better than the green diode laser (=532 nm). The smaller photovoltaic phenomena are mainly due to inefficiently photonic energy for electronic excitation. The thickness of ceramic sample will also affect photovoltaic effect, in which the thinner sample exhibit better photovoltaic effect. With poling by external electric field, the photovoltaic effects under illumination of =405 nm increase with rising of poling intensity.
Lee, Yi-Hsien, i 李奕賢. "Crystal growth and characterizations of multiferroic BiFeO3 thin Films". Thesis, 2005. http://ndltd.ncl.edu.tw/handle/79896347569589551198.
Pełny tekst źródła國立清華大學
材料科學工程學系
94
Multiferroics BiFeO3 (BFO), exhibiting simultaneously ferroelectricity (Tc~1100K) and anti-ferromagnetism (TN~640K), have attracted extensively attention for their coupled electric, magnetic, and structure order parameters in the same phase. The crystal structure, chemical configuration, nanoscale characterization, electric and magnetic properties were investigated is this study. The pure perovskite phase of BFO films were deposited by rf-magnetron sputtering at low processing temperature. The crystal structure of the BFO films was significantly influenced by the substrate and the bottom electrodes. The BFO film was grown with random orientation on Pt/TiOx/SiO2/Si (Pt), whereas highly (100)- and (111)-oriented ones were obtained on LaNiO3/Pt/TiOx/SiO2/Si (LNO) and BaPbO3/Pt/TiOx/SiO2/Si (BPO), respectively. The BFO-based films were hetero-epitaxially grown on the LaNiO3/LaFeO/MgO single crystal substrates. The chemical configuration of the films, which significantly depended on working pressure and temperature, was enhanced by well-controlled processing parameters. The orientation dependence in the crystal growth, electric properties and magnetic behavior of BFO films were examined. The film/electrode interface and chemical homogeneity of the films were characterized by the scanning transmission electron microscope high-angle annular dark-field imaging (STEM-HAADF). Nanoscale characterization of the BFO films was studied by scanning probe microscopy (SPM). With the partial substitution of lanthanum (La) ions for bismuth ions, the significant enhancement in the dielectric, ferroelectric and magnetic performance of BFO films was attributed to the improved crystallinity, smooth surface, and increased lattice volume.
Amrillah, Tahta, i 安泰達. "Multiferroic Properties of BiFeO3-CoFe2O4 Epitaxial Nanocomposite Thin Film". Thesis, 2014. http://ndltd.ncl.edu.tw/handle/22604706933633806236.
Pełny tekst źródła國立交通大學
電子物理系所
102
BFO-CFO vertically align nanocomposite (VAN) was successfully made by utilizing the different wetting conditions from BFO and CFO film when growing on STO substrate at the same time in the PLD system. From the XRD result, there was strain effect from STO substrate to BFO and CFO film. Especially for BFO-CFO/STO VAN, CFO pillar relaxed the strain of BFO film, and shifted magnetic phase transitions on BFO/STO thin film to around 30 K and 160 K as compared to that of BFO powders where the transitions occured around 55 K and 200 K, respectively. From M-T and C-T measurements on BFO/CFO/STO bilayer and BFO-CFO/STO VAN, antiferromagnetic-ferromagnetic coupling (BFO-CFO) is stronger than antiferromagnetic-ferroelectric coupling (BFO). making the magnetization and capacitance anomalies unobservable in those systems. Furthermore, the C-T beharviors of BFO/STO and BFO/CFO/STO are in general similar, but different in subtle details, which presumably originates from the quenching of spin reorientation in BFO due to ferromagnetic coupling from CFO. The situation is even more complicated in the CFO pillar embedded in BFO matrix sample. Finally, from R-T measurement, the high-density BFO-CFO/STO VAN film showed an apparent insulator-metal transition around 30 K, which is similar to that observed in BFO film under strong external magnetic fields which done by another reseach before. The result suggests that when the pillar density is large enough it may generate strong enough local magnetic field to modify the ferroelectric domain structures in BFO matrix. Further investigations are certainly in order to delineate the interisting emergent phenomena observed in the present study.
Bao, Zueng-en, i 鮑正恩. "The ferroelectric property of La and Pb codoped multiferroic BiFeO3". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/72jq57.
Pełny tekst źródłaDing, Jiun-jang, i 丁俊彰. "Synthesis of multiferroic BiFeO3 nanowries by tataric acid gel process". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/70051328437818021438.
Pełny tekst źródła國立成功大學
材料科學及工程學系碩博士班
97
One-dimensional nano-structures have generated considerable interest, due to their unique and superior qualities opposite bulk structures. The investigation in BiFeO3(BFO) material is to transform its morphology into nanowires. The BiFeO3 compound is one of the few materials with coexistent ferroelectricity (TC =810℃) and antiferromagnetism (Neel temperature TN =380℃) at room temperature. Therefore, BFO material is considered to have the great potential for applications in magnetic as well as in ferroelectric devices. Though BiFeO3 was discovered in the 1960’s, but it has the week use in the field of electronics for several reasons: one is that Bi and Fe atoms make it hard form BiFeO3 single phase and ionic iron valence changes from tervalency to bivalence easily result in BiFeO3 has quite high leakage current. In the other hand BiFeO3 its low dielectric constant and resistance make it hard to measure hysteresis loop; furthermore BiFeO3 single phase cannot be synthesized by solid state method and it often includes Bi2Fe4O9、Bi25FeO40 etc impurity phases. Recently, it has generated considerable interest, being a material with great potential applications, by a combination of its magnetic and electric properties in the field of electronics: radio, television, audio-video and digital recording, and as permanent magnets. Thus, the synthesis of bismuth ferrite materials subject of renewed research and attempts have been made to obtain a pure phase. There are two major preparation technique, solid-state reactions based on Bi2O3 andFe2O3 have been used, with thermal treatments around 800°-830℃, but unreacted Bi2O3/ Bi2Fe4O9 were present and removed by washing with HNO3.. Another chemical method includes simultaneous precipitation / coprecipitation involving starting solutions such as Bi and Fe nitrates with ammonium hydroxide and sol-gel method to obtain pure-phase BiFeO3 .Nano-stucture synthesis is the new technique for the last decades. So, the subject of the research is to change BFO material structure by recently nano-techniques and hope to get better physical qualities. In the literature[40], BFO nanowires synthesis has successful done by NCA (porous nanochannel alumina) template, but in the study represents another BFO nanowires synthesis in Si substrate without using NCA template.
Tung, Chiao-Kai, i 董兆凱. "Influences of strain on multiferroic properties of BiFeO3 thin films". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/60702676746344100953.
Pełny tekst źródła國立交通大學
材料科學與工程學系
98
Magnetoelectric multiferroic materials which have coupled electric, and magnetic, that result ferroelectricity and ferromagnetism . These compounds are explored in transition-metal-oxide that present great opportunities for applications in information storage, sensors and green materials. BiFeO3 (BFO)is a room-temperature , single- phase magnetoelectric multiferroic which present ferroelectric polarizations along <111> directions and G-type anti-ferromagnetism . Our study suggests an isostructural change can be induced by epitaxial strain, which is usually driven by temperature or high pressure in solids. Such a transition can induce large displacement of ions that causes high polarizations and show great potential for green piezoelectrics. By using substrates with different lattice parameters for the growth of BFO thin films ,we can get different strain states. In order to fully understand how these strains affect the structure, polarization rotation, ferroelectric domains and environment of ions, we have several techniques to build the framework. X-ray analysis ,such as reciprocal space mapping has been used to understand the structure correlation with strain states. Piezoresponce microscopy has been used to probe the ferroelectric domains .We can also find how the local environment of iron and oxygen ions changed by using X-ray absorption near edge structure (XANES).
TengChi, Lin, i 林灯祺. "Phase Transition and BaTiO3-Doping Effect in Multiferroic BiFeO3 Ceramics". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/05908433999197058974.
Pełny tekst źródła輔仁大學
物理學系
98
In-situ high-resolution synchrotron X-ray diffraction reveals a local minimum in rhombohedral distortion angle αR (associated with an inflection in the lattice constant aR) in the region of 350 ~ 400 oC in BiFeO3 (BFO) and 5 mol% BaTiO3-doped BiFeO3 (BiFeO3(0.95)-BaTiO3(0.05)). It confirms a coupling of ferroelectric and magnetic parameters near the Néel temperature, which is responsible for frequency-dependent maxima in dielectric permittivity. A rhombohedral–cubic structure transition occurs near 850 and 830 oC in BiFeO3 and BiFeO3(0.95)-BaTiO3(0.05), respectively. The BaTiO3-doping can enhance dielectric and ferromagnetic responses, and reduce electric leakage. The dielectric loss of BiFeO3(0.95)-BaTiO3(0.05) remains less than 0.04 below 150 oC.
Wang, Tzu Hsiang, i 王子翔. "Synthesis and Characterization of (Ba,Ti) Substituted BiFeO3 Multiferroic Ceramics". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/26720423799274273711.
Pełny tekst źródła輔仁大學
應用科學與工程研究所博士班
100
A one-dimensional conductivity barrier model with intrinsic barrier B every lattice constant a and extrinsic barrier B+Δ is introduced to describe the dielectric response and conductivity as functions of temperature and frequency. Temperature- and frequency-dependent dielectric permittivity (ε′) and conductivity (σ′) have been studied on multiferroic BiFeO3 (BFO), (1-x)BiFeO3-(x)BaTiO3 (BFO-BT), and (Bi1-xBax)(Fe1-xTix)O3 [BFO-(Ba,Ti)] ceramics, which were synthesized by the solid state reaction method. A frequency-dependent dispersion of dielectric maximum appears in the lower temperature region. This phenomenon is likely activated by the antiferromagnetic (AFM)-paramagnetic (PM) transition. Good qualitative fits of dielectric permittivity and conductivity are obtained with the interior grain sizes d of 20-40 nm. BFO-BT and BFO-(Ba,Ti) ceramics show higher intrinsic barriers B about 11000 K than B=8200 K in BiFeO3. The phase transition of BFO is rhombohedral (R)-orthorhombic (O)-cubic (C) and the Curie temperature (Tc) is near 850 ℃. The structure transition sequence of BFO-BT and BFO-(Ba,Ti) ceramics is R to C upon heating. The Curie temperatures in BFO-BT and BFO-(Ba,Ti) ceramics shift toward lower temperatures due to the contents of (Ba,Ti). The lattice constant in BFO is about 3.9699 Å and increases with increasing the (Ba,Ti) contents. The local minima of R distortion angle (αR) in BFO, BFO-BT, and BFO-(Ba,Ti) occur in the region of 300-500 ℃, implying ionic displacements. The temperature regions also associate with Nèel temperature (TN). This anomaly is likely resulted from the antiferromagnetic (AFM)–paramagnetic (PM) transition and is responsible for the broad frequency-dependent dielectric maximum. The dielectric permittivities are about 33 in BFO and 321 in BFO-30%BT for 1 MHz at room temperature. The dielectric loss decreases as BT increases. The real part of conductivity in BFO shows a deviation from the linear relation near Tm and αR. The deviation temperature shifts to lower temperature with increasing BT contents. BFO and BFO-BT ceramics exhibit a similar antiferromagnetic (AFM) behavior. BFO-5%(Ba,Ti) shows the weak ferromagnetic behavior. The magnetic hysteresis loop of possible iron oxide in BFO-10%(Ba,Ti) was observed due to higher sintering temperature.
Kothai, V. "On the Factors Influencing the Stability of Phases in the Multiferroic System BiFeO3-PbTiO3". Thesis, 2015. http://etd.iisc.ac.in/handle/2005/3949.
Pełny tekst źródłaKothai, V. "On the Factors Influencing the Stability of Phases in the Multiferroic System BiFeO3-PbTiO3". Thesis, 2015. http://etd.iisc.ernet.in/2005/3949.
Pełny tekst źródłaYan, Wei-De, i 顏維德. "Cobalt-Doping Effects on Photovoltaic and Structural Properties in BiFeO3 Multiferroic Ceramics". Thesis, 2014. http://ndltd.ncl.edu.tw/handle/86161909726900075810.
Pełny tekst źródła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.
Yang, Jan-Chi, i 楊展其. "Advanced Engineering of Multiferroic BiFeO3: A Roadmap from Domain Wall, Structure to Functionalities". Thesis, 2014. http://ndltd.ncl.edu.tw/handle/26131191070456830385.
Pełny tekst źródła國立交通大學
材料科學與工程學系所
103
Multiferroics - materials that exhibit coexistence of different ferroic order parameters - have offered a new route to create intriguing functionalities for next generation nanoelectronics. Bismuth ferrite, BiFeO3, is currently the most studied single-phase multiferric, because BiFeO3 is the only room temperature multiferroic in the world to date. In this dissertation, domain engineering of BiFeO3 is explored to create well-controlled domain patterns and desired domain walls, which are used to gain further understanding on the intriguing functionalities of this room-temperature multiferroic. In addition to domain engineering, epitaxial strain engineering is another main focus in this dissertation. The fabrication of newly-developed and non-equilibrium phases of BiFeO3 is achieved by choosing misfit substrates and suitable growth conditions, allowing original properties to be tailored by epitaxial strains. In this dissertation, a new orthorhombic phase of the multiferroic BiFeO3 is stabilized by exerting proper tensile strain, leading to the formation of functional 90o domain walls. On the other hand, with precisely controlled compressive strain, a highly strained BiFeO3 phase is found to exhibit electric controllable magnetism. This dissertation is written to offer a roadmap to reach advanced control on multiferroic BiFeO3, with the hope to explore new opportunities for novel multifunctional devices and nanoelectronics.
Sil, Anomitra. "Structural, Magnetic and Electrical Studies of Multiferroic BiFeO3 and CuO Epitaxial Thin Films". Thesis, 2018. https://etd.iisc.ac.in/handle/2005/4368.
Pełny tekst źródłaWójcik, Katarzyna. "The synthesis, structure and reactivity of iron-bismuth complexes : Potential Molecular Precursors for Multiferroic BiFeO3". Doctoral thesis, 2009. https://monarch.qucosa.de/id/qucosa%3A19322.
Pełny tekst źródłaTripathy, Satya Narayan. "Phase Transition and Magnetoelectric Properties of BiFeO3-RMnO3 (R: Y3+, Gd3+, Dy3+) and Bi1-xBaxFe1-xZrxO3 Multiferroic Nanoceramics". Thesis, 2015. http://ethesis.nitrkl.ac.in/6680/1/Satya_N._Tripathy.pdf.
Pełny tekst źródłaSaha, Surajit. "Phonon Anomalies And Phase Transitions In Pyrochlore Titanates, Boron Nitride Nanotubes And Multiferroic BiFeO3 : Temperature- And Pressure-Dependent Raman Studies". Thesis, 2010. https://etd.iisc.ac.in/handle/2005/2244.
Pełny tekst źródłaSaha, Surajit. "Phonon Anomalies And Phase Transitions In Pyrochlore Titanates, Boron Nitride Nanotubes And Multiferroic BiFeO3 : Temperature- And Pressure-Dependent Raman Studies". Thesis, 2010. http://etd.iisc.ernet.in/handle/2005/2244.
Pełny tekst źródłaWójcik, Katarzyna [Verfasser]. "The synthesis, structure and reactivity of iron-bismuth complexes : potential molecular precursors for multiferroic BiFeO3 / vorgelegt von Katarzyna Wójcik". 2010. http://d-nb.info/1007641886/34.
Pełny tekst źródłaAllen, Marc Alexander. "Theoretical determination of electric field-magnetic field phase diagrams of the multiferroic bismuth ferrite". Thesis, 2014. http://hdl.handle.net/1828/5628.
Pełny tekst źródłaGraduate
0607
0611
marca@uvic.ca
Allen, Marc Alexander. "Theoretical investigation of size effects in multiferroic nanoparticles". Thesis, 2020. http://hdl.handle.net/1828/11972.
Pełny tekst źródłaGraduate
Agrawal, Binit Kumar. "Synthesis of Multiferroic $BiFeo_3$ Material by Autocombustion Technique". Thesis, 2009. http://ethesis.nitrkl.ac.in/1315/1/synthesis_of_multiferroic_BiFeO3_material_by_autocombustion_technique.pdf.
Pełny tekst źródłaChang, Chih-Chia, i 張志嘉. "Fabrication and Characterization of Si-doped or La-doped BiFeO3 Multiferroics Thin Films". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/68061565606033552667.
Pełny tekst źródła國立成功大學
材料科學及工程學系碩博士班
94
Multiferroics BiFeO3 (BFO) thin films which simultaneously coexists ferroelectricity and antiferromagnetism, have attracted extensively attention to applying on memory, tunable sensor and spin transistor. Because of the significant leakage of BiFeO3, the ferroelectric hysteresis can’t measure at room temperature. Si-doped and La-doped BFO thin films were deposited LaNiO3/Si substrates by chemical solution method in this study. Doping effects on crystal structure, leakage current, dielectric, ferroelectric and magnetic properties were investigated. Because the radius of Si4+ ion was much smaller than that of Fe3+, a high temperature annealing process was necessary to induce Si4+ ion to substitute Fe3+ ion. The annealing temperature for Si-doped BFO thin films was 650℃, but the impurity phase (Bi2Fe4O9) was always occured in BFO thin films. The solubility of Si ion was about 5 mole%. Si-doped in BFO thin films would make films dense, reduce crystal size, vacancies, and surface roughness. From dielectric analyses, 5BFSO thin films got a smallest tanδ at low frequency. That’s why leakage current densities of 5BFSO thin films were reduced from 1.58×10-4 (A/cm2) to 1.09×10-7 (A/cm2). The remnant polarization and coercive field of 5BFSO thin films which measured at room temperature were 2.94 (μm/cm2) and 100.1(kV/cm), respectively. The remnant magnetization and coercive magnetic field were increased with increasing the amounts of Si-doped in BFO thin films. The dopant of La would inhibit the formation of Bi2Fe4O9 phase, resulting in increasing dielectric constant. But as the amounts of La-doped in BFO thin films were increased to 15 mole%, grains appeared to be discontinuous. That’s the reason why 15BLFO had a large leakage current density. 10BLFO had the lowest leakage current density of 2.02×10-5(A/cm2) for La-doped in BFO thin films. But this value was still too high to have complete P-E analyses. The remnant magnetization increased as the amounts of La-doped in BFO thin films increased, but the coercive magnetic field was decreased as the amounts of La-doped in BFO thin films increased.
Schwinkendorf, Peter. "Magnetoelektrische Kopplung in BaTiO3- und BiFeO3-Kompositschichten und Leitfähigkeitsphänomene in Sr2FeMoO6-Dünnschichten". 2017. https://ul.qucosa.de/id/qucosa%3A21173.
Pełny tekst źródłaHohenberger, Stefan. "Magnetoelectric Coupling in BaTiO3-BiFeO3 Multilayers: Growth Optimization and Characterization". 2020. https://ul.qucosa.de/id/qucosa%3A73842.
Pełny tekst źródłaGhosh, Sharmistha. "DIELECTRIC RELAXATION SPECTROSCOPY AND ELECTRO-OPTICAL STUDIES OF ANTIFERROELECTRIC AND FERROELECTRIC LIQUID CRYSTALS AND LIQUID CRYSTAL NANO-COMPOSITES". Thesis, 2019. http://hdl.handle.net/10821/8328.
Pełny tekst źródłaThe research was conducted under the supervision of Prof. Subir Kumar Roy of the Spectroscopy division under SPS [School of Physical Sciences]
The research was carried out under IACS fellowship and DST research grant