To see the other types of publications on this topic, follow the link: Perovskites oxides.
Dissertations / Theses on the topic 'Perovskites oxides'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Perovskites oxides.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Akbarian-Tefaghi, Sara. "Microwave-Assisted Topochemical Manipulation of Layered Oxide Perovskites: From Inorganic Layered Oxides to Inorganic-Organic Hybrid Perovskites and Functionalized Metal-Oxide Nanosheets." ScholarWorks@UNO, 2017. http://scholarworks.uno.edu/td/2287.
Full textAbstract:
Developing new materials with desired properties is a vital component of emerging technologies. Functional hybrid compounds make an important class of advanced materials that let us synergistically utilize the key features of the organic and inorganic counterparts in a single composite, providing a very strong tool to develop new materials with ”engineered” properties. The research presented here, summarizes efforts in the development of facile and efficient methods for the fabrication of three- and two-dimensional inorganic-organic hybrids based on layered oxide perovskites. Microwave radiation was exploited to rapidly fabricate and modify new and known materials. Despite the extensive utilization of microwaves in organic syntheses as well as the fabrication of the inorganic solids, the work herein was among the first reported that used microwaves in topochemical modification of the layered oxide perovskites. Our group specifically was the first to perform rapid microwave-assisted reactions in all of the modification steps including proton exchange, grafting, intercalation, and exfoliation, which decreased the duration of multi-step modification procedures from weeks to only a few hours. Microwave-assisted grafting and intercalation reactions with n-alkyl alcohols and n-alkylamines, respectively, were successfully applied on double-layered Dion-Jacobson and Ruddlesden-Popper phases (HLaNb2O7, HPrNb2O7, and H2CaTa2O7), and with somewhat more limited reactivity, applied to triple-layered perovskites (HCa2Nb3O10 and H2La2Ti3O10). Performing neutron diffraction on n-propoxy-LaNb2O7, structure refinement of a layered hybrid oxide perovskite was then tried for the first time. Furthermore, two-dimensional hybrid oxides were efficiently prepared from HLnNb2O7 (Ln = La, Pr), HCa2Nb3O10, HCa2Nb2FeO9, and HLaCaNb2MnO10, employing facile microwave-assisted exfoliation and post-exfoliation surface-modification reactions for the first time. A variety of surface groups, saturated or unsaturated linear and cyclic organics, were successfully anchored onto these oxide nanosheets. Properties of various functionalized metal-oxide nanosheets, as well as the polymerization of some monomer-grafted nanosheets, were then investigated for the two-dimensional hybrid systems.
2
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.
Full text
3
Erten, Onur. "Electronic and Magnetic Properties of Double Perovskites and Oxide Interfaces." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1376496346.
Full text
4
Josepha, Elisha A. "Topochemical Manipulation of Layered Perovskites." ScholarWorks@UNO, 2011. http://scholarworks.uno.edu/td/464.
Full textAbstract:
Topochemical strategies, techniques that allow one to effectively manipulate the structures of nonmolecular solids once a crystal lattice is established, are effective in the low temperature (< 500 °C) modification of solid state structures, allowing the preparation of nonmolecular compounds not accessible by standard synthetic routes. Some of the techniques, ion exchange, intercalation/deintercalation, have proven to be excellent synthetic methods for preserving specific frameworks. The combination of these techniques can allow one to create a multistep approach that can be used to design new compounds with interesting properties.
As an expansion to the field of topotactic reactions, a multistep approach was developed towards the synthesis of the new compounds (A xM0.5Cly)LaNb2O7 (where A = Rb, Cs; M = Fe, Ni; x ≈ 1.5;y ≈ 1) at temperatures below 400oC. The first reaction step involved the ion exchange of the host materials (ALaNb2O7, A = Rb, Cs) to form the products M0.5LaNb2O7 (where M = Fe, Ni), a structure open to further chemistry. The next step involved reductive intercalation with Rb or Cs metal to form the air sensitive mixed-valence products with the nominal compositions, A1.5M0.5LaNb2O7. The last step involved the oxidative intercalation of chlorine using chlorine gas to obtain the final compounds. This multistep approach is a design to form mix-metal halide layers, specifically those with divalent cations, within layered perovskites, opening the doors to compounds that can have interesting properties.
This reaction series was also applied to the tantalate layered oxides, leading to the formation of the new compound Ni 0.5LaTa2O7 through ion exchange. The further multistep
topochemical manipulation of this new compound was not successful and was indicative of the difference in chemical behavior of the tantalates versus the niobates.
We have also investigated the oxidative intercalation of halogens into a series of Ruddlesden-Popper (R-P) ruthenate oxides with the formula Ae n+1RunO3n+1 (Ae = Ca, Sr; n = 1, 2, 3) using several sources of fluorine, chlorine, and bromine. A new method was developed to intercalate chlorine into layered systems; this new approach avoids the use of chlorine gas which is highly toxic. The new phase Sr3Ru2O7Cl0.7 was synthesized by the new method and further topotactic manipulations were explored. The chemistry was not limited to the n = 2 phase but was also applied to the n = 3 phase, Sr4Ru3O10.
5
Gustin, Lea. "Synthesis and Topochemical Manipulation of New Layered Perovskites." ScholarWorks@UNO, 2016. http://scholarworks.uno.edu/td/2149.
Full textAbstract:
Metastable layered perovskites containing interlayer transition metals can readily be obtained by simple ion exchange reactions on receptive hosts, such as those of the Dion-Jacobson and Ruddlesden-Popper structure types. In this work, we focused on adding to the library of layered perovskites by not only creating new compounds, but by also showing their ability to be further manipulated, and by studying the stability of the series through thermal behavior studies.
The reactions with transition metal halides are particularly interesting since they often lead to novel architectures and magnetic behavior. On subsequent heat treatment, these exchange products typically decompose to thermodynamically more stable phases. The newly synthesized spin glass-like material, FeLa2Ti3O10, obtained by ion exchange of Li2La2Ti3O10 with FeCl2 at 350 °C, behaves differently. When heated to 700 °C, the compound undergoes a significant cell contraction (Δc ≈ -2.7 Å) with an increase in the oxidation state of iron present in the interlayer that not been observed before in such compounds. Efforts were also made to synthesize new series of compounds, here MSrTa2O7 (M= Co and Zn), with vacancies in the interlayer that could lead to future topochemical manipulations.
The ability to vary the composition of different phases to form solid-solutions through atomic substitution at the A or B sites with ions of similar or different charge can lead to new structures as well an enhancement of the properties of the original compound or new ones. The synthesis and characterization of the new mixed A-cation containing layered perovskite RbLaNaNb3O10, where La3+ and Na+ share the same site in the perovskite slab and RbLaCaNb2MnO10 that exhibits an ordering of the B site with Mn in the center of the perovskite slab will be presented. Further topochemical manipulation of these phases via ion exchange reactions at low temperatures (< 500 °C), lead to the new series A’LaNaNb3O10 and A’LaCaNb2MnO10 where A’= H, Li, Na, K and CuCl.
6
Awin, Labib Ali Mohamed. "Structural, Magnetic And Electrical Studies On Some Mixed Metal Perovskite Oxides." Thesis, The University of Sydney, 2013. http://hdl.handle.net/2123/9531.
Full textAbstract:
This thesis describes crystallographic, magnetic and electrical studies of some mixed metal perovskites. In the first part, the charge distribution, magnetic and electrical properties of mixed metal rhodium-copper perovskite oxides were investigated. Various series with the general formula Ln1-yAyRh1-2xCuxBxO3 in which (Ln = La3+, Tb3+; A = Ca2+, Sr2+, Pb2+, Bi3+; B = Sc3+, Cu2+, Zn2+ ; y ≤ 0.3, x ≤ 0.25), have been synthesised by solid state reaction, and characterised by X-ray diffraction, scanning electron microscopy and physical property measurements and, as available, neutron diffraction and X-ray absorption near edge structure measurements. Structures were invariably orthorhombic with space group Pbnm with the Rh and Cu ions disordered on the same site. X-ray diffraction measurements of selected samples showed that the orthorhombic structure persisted over a wide temperature range, 30 to 900 ºC. All the samples are semiconductors and paramagnetic over the temperature range 4-300 K. Doping a divalent cation onto the B site appears to have a significant impact on charge delocalization between Rh3+/4+ and Cu2+/3+ ions due to the oxidation of Rh3+ to Rh4+ required to maintain the overall charge. That was most evident from the Rh L3 XANES measurements of the LaRh1-2xCu2xO3 and La1-xPbxRh0.5Cu0.5O3 series. Powder neutron diffraction measurements of La0.75Pb0.25Rh0.5Cu0.25Zn0.25O3, LaRh0.5Cu0.25Zn0.25O3 and La0.75Pb0.25Rh0.5Cu0.5O3 show no evidence for anion vacancies and it is postulated the oxides do not contain appreciable amount of oxygen vacancies. The magnetization curves show negative values for Weiss constants indicating weak antiferromagnetism may be present but there is no indication for long range coupling in the oxides. There are several factors that may influence the magnitude of the cell volume, octahedral distortion, octahedral tilting, magnetic interactions and electronic properties. These include ionic size, effective charge, electron configuration and electronegativity. In addition the charge delocalization and local ordering effects can play a role. The present work has demonstrated that: The changes in the unit cell volume and the octahedral distortion of the isovalent doped oxides such as La0.75A0.25Rh0.7Cu0.3O3 where A = Ca2+, Sr2+ and Pb2+ are consistent with the increase in the ionic radii, whereas the decrease in magnetic moments of these is correlated with the increase in the electronegativities of the dopant cation. The unit cell volumes for the terbium oxides are somewhat smaller than found in the analogous lanthanum oxides reflecting the small ionic size of Tb3+. The divalent cation doped oxides LnRh1-2xCu2xO3 and LnRh1-2xCuxZnxO3 display lower cell volumes and octahedral distortions but higher magnetic moments and electrical conductivities than the trivalent cation doped oxides LnRh1-2xCuxScxO3 as consequence of charge delocalization. The electrical conductivity of the oxides increases as the divalent dopant content increases possibly because of an increase in carrier concentration that occurs as consequences of the formation of ionic defects due to the oxidation of Rh3+ (3d6) to Rh4+ (3d5). The electron configuration influences the spin coupling and the band gap and this is most evident in the Pb2+ and Bi3+ (6s2) doped LaRh1-2xCu2xO3 oxides which exhibited the lowest magnetic moments and the highest activation energies among the oxides studied. Compared with the analogous lanthanum oxides, the magnetic susceptibilities of the terbium oxides increased as a consequence of the contribution of Tb3+ 4 f8 electrons. Changing the A site composition resulted in anomalous changes in the cell volumes, octahedral distortions, electrical resistivity and magnetic susceptibility of the La1-xPbxRh0.5Cu0.5O3 and La1-xBixRh0.5Cu0.5O3 perovskites. This is likely a consequence of charge delocalization and short-range local ordering effects. Increasing the doping on the B-site resulted in either a decrease or increase in the cell volumes and the magnetic moments, depending on the dopant type cation. The final part of this thesis describes the structure of some Ba2-xSr1+xBO5.5 (B = Nb5+ and Ta5+) perovskites. These were characterised by scanning electron microscopy, thermogravimetric analysis, X-ray and neutron diffraction. The preparation of these used solid state methods but the initial reactions were conducted under different media. Four compounds were prepared and these all have a face centred cubic structure with space group Fm3 ̅m. The two synthetic methods produce monophasic powders and these differ in color, particle size, and hardness. The cell edges of the oxides obtained by mixing the reactants with water are larger than these obtained when the mixing was conducted with acetone. The neutron diffraction profiles demonstrate that the A cation and oxygen ions are disordered in the BaSr2NbO5.5 and BaSr2TaO5.5 structures. The unusual thermal expansion of the unit cell is due to the presences of water and anion deficiency into the oxides structure. The oxides were found to absorb CO2 atmosphere during storage.
7
Johnston, Karen Elizabeth. "A complementary study of perovskites : combining diffraction, solid-state NMR and first principles DFT calculations." Thesis, University of St Andrews, 2010. http://hdl.handle.net/10023/1837.
Full textAbstract:
Perovskites, ABX₃, and their associated solid-solutions are a particularly important and attractive area of research within materials chemistry. Owing to their structural and compositional flexibility and potential physical properties they are one of the largest classes of materials currently under investigation. This thesis is concerned with the synthesis and structural characterisation of several perovskite-based materials using a combined approach of high-resolution synchrotron X-ray and neutron powder diffraction (NPD), solid-state Nuclear Magnetic Resonance (NMR) and first-principles Density Functional Theory (DFT) calculations. Initial investigations concentrated on room temperature NaNbO₃, a perovskite widely debated in the literatue. Published crystallographic data indicate NaNbO₃ possesses two crystallographically distinct Na sites in space group Pbcm. Whilst some of our materials appear in agreement with this (notably a commercially purchased sample) many of our laboratory-synthesised samples of NaNbO₃ routinely comprise of two phases, which we show to be the antiferroelectric Pbcm and polar P2₁ma polymorphs. Several different synthetic methods were utilised during this investigation and the quantity of each phase present was found to vary as a function of preparative method. ²³Na, ⁹³Nb and ¹⁷O DFT calculations were used in conjunction with experiment to aid in spectral analysis, assignment and interpretation. In addition, ab initio random structure searching (AIRSS) was utilised in an attempt to predict the most stable phases of NaNbO₃. This proved to be both successful and highly informative. A series of NaNbO₃-related solid-solutions, namely K[subscript(x)]Na[subscript(1-x)]NbO₃ (KNN), Li[subscript(x)]Na[subscript(1-x)]NbO₃ (LNN) and Na[subscript(1-x)]Sr[subscript(x/2)]□[subscript(x/2)]NbO₃ (SNN) have also been synthesised and characterised. The substitution of K⁺ , Li⁺ and Sr²⁺ cations onto the A site appears to produce the same polar P2₁ma phase initially identified in the room temperature NaNbO₃ investigation. The abrupt change in cation size in the KNN and LNN series, and the introduction of vacancies in the SNN series, is thought to result in a structural distortion which, in turn, causes the formation of the P2₁ma phase. A low temperature synchrotron X-ray powder diffraction study (12 < T < 295 K) was completed for a sample of NaNbO₁ composed of the P2₁ma polymorph (~90%) and a small quantity of the Pbcm phase (~10%). A region of phase coexistence was identified between the P2₁ma, R3c and Pbcm phases over a relatively large temperature range. Full conversion of the P2₁ma phase to the low temperature R3c phase was not possible and, consistently, the P2₁ma phase was the most abundant phase present. Factors such as structural, strain, crystallite size and morphology are thought to be crucial in determining the exact phases of NaNbO₃ produced, both at low and room temperature. The solid-solution La[subscript(1-x)]Y[subscript(x)]ScO₃ was also investigated. Compositions x = 0, 0.2, 0.4, 0.6, 0.8 and 1 were successfully synthesised and characterised. Refined high-resolution NPD data indicates that an orthorhombic structure, in space group Pbnm, was retained throughout the solid-solution. Using ⁴⁵Sc and ⁸⁹Y MAS NMR each sample was found to exhibit disorder, believed to result from both a distribution of quadrupole and chemical shifts. NMR parameters were calculated for several model Sc and Y compounds using DFT methods to determine the feasibility and accuracy of ⁴⁵Sc and ⁸⁹Y DFT calculations. These proved successful and subsequent calculations were completed for the end members LaScO₃ and YScO₃. DFT calculations were also utilised to gain insight into the disorder exhibited in the La[subscript(1-x)]Y[subscript(x)]ScO₃ solid-solution.
8
Shah, N. "Structure-property correlations in layered perovskites and related oxides: importance of atomic sizes." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 1995. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2842.
Full text
9
Zong, Yanhua. "Magnetic and magnetodielectric properties of Eu2+-containing oxides." 京都大学 (Kyoto University), 2010. http://hdl.handle.net/2433/126809.
Full text
10
Vivek, Manali. "Etats topologiques aux surfaces de perovskites d'oxydes de métaux de transition." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS216/document.
Full textAbstract:
Le sujet de la topologie dans les oxydes, en particulier à la surface des oxydes de pérovskite comme SrTiO₃, ou à l'interface de LaA1O₃ / SrTiO₃ sera étudié dans cette thèse. Les deux matériaux, à leurs surfaces orientées (001), contiennent un état métallique limité à quelques nanomètres de la surface. De plus, nous montrerons qu'il existe certains croisements de trois bandes autour desquelles des perturbations vont provoquer l'apparition d'un spectre de bandes inversées et gappées. Ceux-ci conduiront à des états de bord topologiques qui peuvent être détectés via la supraconductivité induite comme dans le cas des puits quantiques topologiques ou des nanofils des supraconducteurs-semi-conducteurs. Ensuite, la surface orientée (111) de LaA1O₃ / SrTiO₃ sera étudiée lorsque les mesures de transport de Hall révèlent une transition de un à deux porteurs par dopage électrostatique. Une explication basée sur un modèle de liaisons fortes incluant des corrélations U de Hubbard sera proposée, ce qui donnera lieu à des croisements de bandes entre les sous-bandes favorisant les états topologiques. Enfin, une étude ab-initio de CaTiO₃ sera effectuée pour expliquer l'état métallique qui existe à sa surface (001) orientée et pour prédire le magnétisme dans le système. CaTiO₃ est différent des autres composés étudiés précédemment, en raison de la grande rotation et de l'inclinaison des octaèdres d'oxygène entourant le Ti, ce qui complique les faits. La structure avec et sans lacunes d'oxygène sera étudiée en profondeur pour fournir des détails sur la bande de conduction et leurs caractères orbitauxThe subject of topology in oxides, in particular at the surfaces of perovskite oxides like SrTiO₃, or at the interface of LaA1O₃/SrTiO₃ will be investigated in this thesis. Both compounds, at their (001) oriented surfaces, contain a metallic state confined to a few nanometers at the surface. In addition, we will show that there exist certain three band crossings around which perturbations will cause an inverted and gapped band spectrum to appear. These will lead to topological edge states which can be detected via induced superconductivity as in the case of topological quantum wells or superconductor-semiconductor nanowires. Next, the (111) oriented surface of LaA1O₃/SrTiO₃ will be studied where Hall transport measurements reveal a one to two carrier transition via electrostatic doping. An explanation based on a tight binding modelling including Hubbard U correlations, will be proposed which will give rise to band crossings between sub-bands promoting topological states. Finally, an ab-initio study of CaTiO₃ will be performed to explain the metallic state which exists at its (001) oriented surface and to predict magnetism in the system. CaTiO₃ is different from the other compounds studied previously, due to the large rotation and tilting of the oxygen octahedra surrounding the Ti, which complicates the picture. The structure with and without oxygen vacancies will be studied in-depth to provide details about the conduction band and their orbital characters
11
Gonzalez, Rosillo Juan Carlos. "Volume resistive switching in metallic perovskite oxides driven by the metal-Insulator transition." Doctoral thesis, Universitat Autònoma de Barcelona, 2017. http://hdl.handle.net/10803/405305.
Full textAbstract:
Los óxidos de perovskita fuertemente correlacionados son una clase de materials con fascinantes propiedades físicas intrínsecas debido a la interacción de efectos de carga, spin, órbita y cristalinos. Efectos exóticos, como superconductividad, ferromagnetismo, ferroelectricidad o transiciones metal-aislante se producen gracias a la competición de los diferentes grados de libertad del sistema. El uso de estos efectos en una nueva generación de dispositivos es una fuente de inspiración continua para la comunidad científica.
Los dispositivos de Memoria Resistiva de Acceso aleatorio (RRAM) son uno de los candidatos más prometedores para ganar la carrera hacia la memoria universal del futuro, debido a sus excelentes propiedades en términos de escalabilidad, fatiga frente a ciclado, retención y velocidad de operación. Están basadas en el efecto de Conmutación Resistiva (RS), dónde dos (o más) estados de resistencia, reversibles y no volátiles son inducidos mediante la aplicación de un campo eléctrico intenso. Este fenómeno ha sido observado en una gran variedad de óxidos, donde es ampliamente aceptado que el movimiento de oxígeno juega un papel fundamental para explicar su origen. Sin embargo, el mecanismo físico preciso que gobierna el efecto depende del material, y en algunos de ellos, dicho mecanismo aún no es comprendido en su totalidad. Esta falta de compresión es hoy en vía es uno de los cuellos de botella que está retrasando el uso generalizado de esta tecnología.
En esta tesis, presentamos un novedoso mecanismo de RS basado en la Transición Metal-Aislante (MIT) perovskitas metálicas con correlación electrónica fuerte. Hemos estudiado el comportamiento RS de tres diferentes familias de perovskitas metálicas: La1-xSrxMnO3, YBa2Cu3O7-d y RENiO3 y demostramos que estos tres sistemas con conducción mixta eletrónica-iónica pueden experimentar una MIT, como consecuencia de la aplicación del campo eléctrico intenso, y que puede transformar su volumen bulk. Esta conmutación resistiva de carácter volúmico tiene una naturaleza diferente the los usuales tipos filamentar e interfacial, y abre nuevas oportunidades para el diseño de nuevos dispositivos robustos.
Hemos caracterizado conciencudamente el efecto de RS a la nanoescala mediante Microscopía de Fuerzas Atómicas en modo Conducción (C-AFM). Espectroscopía de Fuerza Túnel (STS) y medidas de transporte dependientes de la temperatura han sido realizadas en los diferentes estados resistivos para obtener detalles de su estructura electrónica. Hemos reproducido con éxito el comportamiento memristivo nanoscópico en una escala micrómetrica mediante el uso de sondas de W-Au en una estación de puntas. Usando esta aproximación, hemos llevado a cabo medidas en diferentes atmósferas, las cuales sugieren el intercambio de oxígeno con la atmósfera. Además, presentamos una prueba de concepto de una configuración de tres terminales, donde la conmutación resistiva es inducida en la puerta del dispositivo. En el caso particular del superconductor YBa2Cu3O7-d, hemos estudiado la influencia en las propiedades superconductoras de zonas de alta resistencia embebidas en la matriz del material. Esta aproximación sienta las bases hacia el diseño de dispositivos con zonas de anclaje de vórtices reconfigurables.
La interpretación de los resultados se hará en términos de una transición volúmica de tipo Mott, que estimamos ser de validez general para perovskitas metálicas de óxidos complejos.Strongly correlated perovskite oxides are a class of materials with fascinating intrinsic physical functionalities due to the interplay of charge, spin, orbital ordering and lattice effects. The exotic phenomena arising from these competing degrees of freedom include superconductivity, ferromagnetism, ferroelectricity and metal-insulator transitions, among others. The use of these exotic phenomena in a new generation of devices with new and enhanced functionalities is continuing inspiring the research community. In this sense, Resistive-Random Access Memories (RRAM) are one of the most promising candidates to win the race towards the universal memory of the future, which could overcome the limitations of actual technologies (Flash and Dynamic-RAM), due to their excellent properties in terms of scalability, endurance, retention and switching speeds. They are based on the Resistive Switching effect (RS), where the application of an electric field produces a reversible, non-volatile change in the resistance between two or more resistive states. This phenomenon has been observed in a large variety of oxide materials, where the motion of oxygen is widely accepted to play a key role in their outstanding properties. However, the exact mechanism governing this effect is material-dependent and for some of them it is still far to be understood. This lack of understanding is actually one of the main bottlenecks preventing the widespread use of this technology. In this thesis, we present a novel Resistive Switching mechanism based on the Metal-Insulator Transition (MIT) in metallic perovskite oxides with strong electron electron interaction. We analyse the RS behaviour of three different families of metallic perovskites: La1-xSrxMnO3, YBa2Cu3O7-δ and RENiO3 and demonstrate that the MIT of these mixed electronic-ionic conductors can be tuned upon the application of an electric field, being able to transform the entire bulk volume. This volume RS is different in nature from interfacial or filamentary type and opens new possibilities of robust device design. Thorough nanoscale electrical characterization of the RS effect in these systems has been performed by means of Conductive-Atomic Force Microscopy (C-AFM). Scanning Tunnelling Spectroscopy (STS) and temperature-dependent transport measurements were performed in the different resistive states to get insight into their electronic features. The nanoscale memristive behaviour of these systems is successfully reproduced at a micrometric scale with W-Au tips in probe station experiments. Using this approach, atmosphere dependent measurements were undertaken, where oxygen exchange with the ambience is strongly evidenced. In addition, we present a proof-of-principle result from a 3-Terminal configuration where the RS effect is applied at the gate of the device. In the particular case of superconducting YBa2Cu3O7-δ films, we have studied the influence of high resistance areas, which are embedded in the material, on the superconducting transport properties enabling vortex pinning modification and paving the way towards novel reconfigurable vortex pinning sites. We interpret the RS results of these strongly correlated systems in terms of a Mott volume transition, that we believe to be of general validity for metallic perovskite complex oxides. We have verified that strongly correlated metallic perovskite oxides are a unique class of materials very promising for RS applications due to its intrinsic MIT properties that boosts a robust volumetric resistive switching effect. This thesis settles down the framework to understand the RS effect in these strongly correlated pervoskites, which could eventually lead to a new generation of devices exploiting the intrinsic MIT of these systems.
12
Eng, Hank W. "The crystal and electronic structures of oxides containing d0 transition metals in octahedral coordination." Connect to this title online, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1070570079.
Full textAbstract:
Thesis (Ph. D.)--Ohio State University, 2003.Title from first page of PDF file. Document formatted into pages; contains xx, 180 p.; also includes graphics. Includes bibliographical references (p. 139-145).
13
Kawrani, Sara. "Synthesis, Characterizations and applications of oxides materials based on CaCu3Ti4O12." Thesis, Montpellier, 2019. http://www.theses.fr/2019MONTS085.
Full textAbstract:
Les oxydes de type pérovskites présentent différentes propriétés selon leur structure et leur composition chimique. Les principales pérovskites étudiées, BaTiO3 et YBa2Cu3O7, possèdent d’intéressantes propriétés ferroélectriques et supraconductrices. Une des limitations de ce type d’oxydes est la transition de phase à haute température qui peut modifier leurs propriétés. Le matériau CaCu3Ti4O12 (CCTO) est un oxyde connu comme double perovskite (ABO3) à structure cubique, qui a été étudié ces dernières années en tant que matériau diélectrique de permittivité élevée. De plus, CCTO subit une transition magnétique à antiferromagnétique au-dessous de la température de Néel (TN=25K). Les propriétés du matériau CCTO sont fortement dépendantes de sa structure et offrent des possibilités d’applications photoélectrochimiques. D'un autre côté, les nanofeuillets de nitrure de bore (h-BN) et d’oxyde de graphène (GO) sont des matériaux 2D présentant des propriétés très intéressantes.Dans le cadre de ce travail, des matériaux composites à base de CCTO et de nanofeuillets de nitrure de bore et d’oxyde de graphène ont été synthétisés et étudiés. Les céramiques composites CCTO/GO et CCTO/h-BN ont été synthétisées par réaction solide-solide. Les différentes propriétés photoélectrochimiques, diélectriques, et magnétiques ont été caractérisées. L’addition de 3% de h-BN aboutit à l’incorporation des atomes du bore et d’azote dans le réseau cristallin du CCTO et forme les liaisons Ti-B-O et Ti-N-O, et génère des lacunes d’oxygène à la surface, ce qui améliore la génération de porteurs de charges. La génération de porteurs de charges est augmentée en 50% par rapport au CCTO pur, après l’addition de 3% de GO, due à l’oxydation de GO à haute température qui réduit Ti4+ et Cu2+ en site actifs Ti3+ et Cu+ respectivement. Les propriétés magnétiques du CCTO avec 6% de nanofeuillets ont été étudiées, et ont montré que la température Néel n’était pas modifiée. Enfin, un polissage est effectué à la surface des céramiques pour étudier leurs propriétés diélectriques. Les résultats montrent des valeurs de permittivité plus basse que celles décrites dans la littérature. En conclusion, ces travaux ont démontré que l’incorporation des nanofeuillets 2D n’affecte pas les propriétés diélectriques et magnétiques, mais améliore considérablement les propriétés photoélectrochimiques du CCTOPerovskite oxides exhibit a large variety of properties because of their structures and chemical compositions. Well known properties of the perovskite oxides are Ferroelectricity in BaTiO3-based oxides and superconductivity in YBa2Cu3O7. The major limit of these compounds is their phase transitions at high temperature, which lead to modify the perovskite properties. CaCu3Ti4O12 (CCTO) exhibit a cubic structure stable at high temperature, it is a double-perovskite (ABO3). CCTO was known as high dielectric material, and can play a key role in photoelectrochemical activity due to its structure. In addition, CCTO can occur a phase transition into the antiferromagnetically ordered phase below Neel temperature TN = 25 K. On the other hand, 2D nanomaterials including graphene oxide (GO) and hexagonal boron nitrides (h-BN) were widely used due their exceptional properties.The aim of this thesis is to investigate the photoelectrochemical, dielectric, and magnetic properties of CCTO based composites. Composites made of CCTO/GO and CCTO/h-BN ceramics were fabricated by solid-state reaction. With the addition of 2D nanosheets materials, the photoelectrochemical performance is enhanced by increasing the generation of photocurrent. CCTO with 3%wt of h-BN showed the insertion of bore (B) and nitrogen (N) into CCTO lattice, leading to Ti-B-O, Ti-N-O bonds and oxygen vacancies on the surface which reduce the bang gap energy and increase the density of generated photocurrent. With 3% of GO, Ti4+ and Cu2+ were reduced to active species Ti3+ and Cu+ respectively and oxygen vacancies were generated at the surface for charge neutralization, leading to generate photocurrent density 50% higher than pure phase of CCTO. In order to investigate 2D nanomaterials effects on magnetic properties of composites, CCTO with 6%wt of nanosheets was prepared and have shown no significant changes in Neel temperature. Finally in the last section, all composites were surface polished to investigate their dielectric properties, measurements showed a low permittivity in comparison to the literature. In conclusion, this work has shown that 2D nanosheets materials incorporation does not affect dielectric and magnetic properties, but enhance strongly the photoelectrochemical behavior of CCTO
14
Rafique, Hafiz Muhammad. "Resonant and high resolution photoemission of rare-earth cobalt oxides." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/resonant-and-high-resolution-photoemission-of-rareearth-cobalt-oxides(33377a1a-670c-413d-a38f-73c52115b5e5).html.
Full textAbstract:
LnBaCo2O5+δ (Ln-112) where Ln = lanthanide element; 0 ≤ δ ≤1 and LnBaCo4O7+δ (Ln-114) are highly correlated cobalt oxides. Synchrotron photoemission spectroscopy of LnBaCo2O5+δ (Ln = Gd, Dy, Dy1-xTbx) and LnBaCo4O7 (Ln = Yb) has been undertaken at the UK Synchrotron Radiation Source (Daresbury Laboratory).During the photoemission experiments, the samples were observed to be contaminated due to residual gases inside the main vacuum chamber. The surface degradation of the samples is studied using the difference spectra generated from the valence band spectra of freshly scraped and contaminated samples and the nature of contaminated species on these samples is identified in the light of the reviewed literature. High-resolution photoemission is carried out to study the metal-insulator (MI) transition in double perovskites LnBaCo2O5+δ (Ln = Gd, Dy, Dy1-xTbx - Ln-112; 0 ≤ δ ≤ 1) as a function of temperature. The high-resolution photoemission results of single crystal samples of GdBaCo2O5.5, DyBaCo2O5.5 and Dy1-xTbxBaCo2O5+δ show that the temperature-based MI transitions in these compounds occur in the 300-400 K temperature range. A post-growth oxygen annealing treatment for as-grown single crystals of Ln-112 is necessary, achieving oxygen contents close to 5.50, to observe a marked nonmetal-to-metal transition. Resonant photoemission is used to identify the atomic parentage of the valence band states. A comparison of the electronic structure of LnBaCo2O5+δ (Ln = Gd, Dy, Dy1-xTbx - Ln-112; 0 ≤ δ ≤ 1) and LnBaCo4O7 (Ln = Yb - Ln-114) single-crystal surfaces is made using synchrotron photoemission spectroscopy. In both cases, the states close to the Fermi energy are found to be of mixed Co 3d/O 2p character, and the comparison allows identification of states due to low spin Co³⁺ in octahedral environments. The contributions from Ln elements to the valence band are found at higher binding energies.
15
Tseggai, Mehreteab. "Synthesis, Nuclear Structure, and Magnetic Properties of some Perovskite Oxides." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4826.
Full text
16
Quattropani, Alessandro. "Synthesis of ferroelectric oxides for photovoltaic applications." Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAD053/document.
Full textAbstract:
Dans ce travail, nous avons étudié la croissance de films d’oxydes Bi2FeCrO6 (BFCO) en utilisant les techniques de sol-gel et dépôt par laser pulsé (PLD). Dans le cas de la voie chimique, des précurseurs en solution ont été préparés, puis déposés par centrifugation sur des substrats de silicium (100) ou de quartz. Les nombreuses analyses structurelles (DRX) et d'imagerie (SEM, TEM) effectuées sur ces films BFCO ont montré que les films sont assez homogènes mais présentent de nombreuses phases parasites qui peuvent être éliminés partiellement par recuit thermique rapide. Des dispositifs tests à base de films BFCO par sol-gel ont été préparés et qui ont montré des propriétés électriques limitées à cause des nombreux défauts. Des films BFCO ont également été produits par la technique PLD sur des substrats STO et NbSTO. Les propriétés structurelles, optiques et électriques sont présentées. La diffusion épitaxiale de haute qualité et les films en phase pure sont démontrés par diffraction des rayons X. Nous avons étudié l'évolution de paramètres tels que la bande interdite en fonction des conditions de croissance, montrant qu'elle peut être ajustée de 1, 9 à 2,6 eV. Ce comportement a été corroboré par des calculs théoriques sur l’arrangement atomique dans la structure BFCO. Les propriétés ferroélectriques sont étudiées par microscopie à force piézoélectrique. La lumière s'est avérée avoir un effet sur la polarisation. Il a également été démontré que la mémoire de la polarisation affecte la réponse photovoltaïque. Enfin, des dispositifs basés sur BFCO sont fabriqués et leurs propriétés photovoltaïques sont analysées. Des valeurs de tension de circuit ouvert de 600mV sont encourageantes pour la nouvelle génération de cellules solairesIn this work, we have produced Bi2FeCrO6 oxides (BFCO) by sol-gel technique and pulsed laser deposition (PLD). By sol-gel, precursors in solution were prepared, which are then deposited by centrifugation on silicon or quartz substrates. The numerous structural (XRD) and optical images (SEM, TEM) analyses carried out on these BFCO films show that the films are fairly homogeneous but exhibit many parasitic phases, which they can be partly eliminated by rapid thermal annealing. Finally, we present the first results obtained on BFCO-SG perovskite devices. On the other hand, BFCO films were deposited on STO and Nb:STO substrates. Their structural, optical and electrical properties are presented. High-quality epitaxial growth and pure-phase films are demonstrated by X-ray diffraction. We show that the band gap of the PLD-BFCO films can be tuned from 1, 9 to 2.6 eV thanks to the variation of growth conditions. Theoretical calculations has confirmed the observed behavior and highlight the importance of the ordering phase. The ferroelectric properties of the PLD films are studied by the piezoresponse force microscopy. Illumination is shown to have a strong effect on polarization. We show that the polarization memory affects the photovoltaic response. Finally, devices based on BFCO are manufactured and their photovoltaic properties are analyzed
17
Bouilly, Guillaume Jacques. "Synthesis and characterization of transition metal oxides and oxyhydrides using epitaxial thin films deposition." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/200450.
Full text
18
Yildirim, Ceren. "Using a perovskite oxide as interfacial layer for halide perovskite optoelectronics." Electronic Thesis or Diss., Limoges, 2024. http://www.theses.fr/2024LIMO0001.
Full textAbstract:
Les cellules photovoltaïques et les diodes électroluminescentes pérovskites requièrent des couches d'injection/extraction de charges, qui sont cruciales pour plusieurs processus importants régissant les performances et la durée de vie. Bien que des études intensives aient été consacrées au développement de couches interfaciales innovantes de type p, des matériaux présentant des propriétés hautement ajustables et une stabilité photochimique élevée restent très recherchés. Cette thèse explore l’utilisation d’oxydes pérovskites comme couches d’interface pour des applications optoélectroniques en raison de leurs propriétés ajustables et de leur stabilité en conditions ambiantes. Des couches minces d’oxydes de pérovskites de type SrTi0.7Fe0.3O3-δ (STFO) sont utilisées comme couches d'extraction ou d'injection de charge pour les cellules solaires et les diodes électroluminescentes à base de pérovskites halogénées. En utilisant la technique de dépôt par laser pulsé (PLD), des couches minces STFO hautement cristallines ont été déposées sur des substrats en verre/FTO à des températures relativement modérées (<400 °C) par rapport aux techniques de dépôt traditionnelles. Des post-traitements thermiques, soit par traitement thermique rapide (RTP), soit par recuit thermique conventionnel (TA), ont été utilisés dans le but d’améliorer la plus grand cristalline des films polycristallins et pour ajuster leurs propriétés optiques et électroniques. Lorsqu'ils sont déposés sur la pérovskite d’oxyde, les couches d'halogénure de pérovskite de type FA0.85Cs0.15Pb(I0.85Br0.15)3 (adaptées à la conversion d'énergie photovoltaïque PV) présentent des tailles de grains plus grandes et un meilleur ordre cristallin par rapport à des films similaires déposés sur une couche interfaciale de type p de référence telle que le PEDOT:PSS commercial. De plus, la présence de l'oxyde a entraîné une nette réduction de la phase de pérovskite halogénée optiquement inactive, illustrant l’impact positif de la couche d’oxyde pérovskite sous-jacente. Les couche de STFO recuites (RTP et le TA) induisent par ailleurs une plus grande durée de vie de l’exciton dans la couche active par rapport au PEDOT :PSS. De façon similaire, la cristallisation d’une pérovskite halogénée quasi-2D de type (PEA)2(MA)PbBr4 (adaptée à la fabrication de LED) sur des couches de STFO a été réalisée avec succès, conduisant à des propriétés similaires que pour des couches références déposées sur du PEDOT:PSS. Dans ce cas, la pérovskite quasi-2D déposée sur STFO a montré une durée de vie de l’exciton relativement longue. Bien que l'intégration de couches minces de STFO dans les deux types de dispositifs ait donné lieu à des performances limitées, ce travail démontre le fort potentiel de la classe des oxydes de pérovskites pour la création de dispositifs tout-pérovskite efficaces et stablesHalide organic-inorganic photovoltaics and light-emitting diodes require suitable charge injection/extraction layers, which are crucial for several important processes governing performance and lifetime. While intensive research has been devoted to developing innovative p-type interfacial layers, materials with highly tunable properties and high photochemical stability remain in demand. This thesis explores oxide perovskites as interlayers for optoelectronic applications due to their stable physical properties under ambient conditions. SrTi0.7Fe0.3O3-δ (STFO) oxide perovskite thin film is utilized as charge extraction/injection layers for planar halide perovskite solar cells and light-emitting diodes. Using pulsed laser deposition (PLD), highly crystalline STFO thin layers on glass/FTO substrates have been successfully processed at relatively moderate temperatures (<400 °C) as compared to traditional deposition techniques. Additional thermal treatments, either by rapid thermal processing (RTP) or conventional thermal annealing, have been applied to the oxide thin films to further improve the larger crystal of the polycrystalline layers, and to tune their optical and electronic properties. When deposited on top of the oxide perovskite, FA0.85Cs0.15Pb(I0.85Br0.15)3 halide perovskite layer (suitable for photovoltaic PV energy conversion) show larger grain sizes and better crystalline order than compared to similar films deposited on top of reference p-type interlayer such as commercial PEDOT:PSS. Furthermore, the presence of the oxide resulted in a clear reduction of the fraction of optically inactive halide perovskite phase. This observation suggests that the perovskite interlayer positively impacts the growth mechanism of the halide perovskite active layer. Finally, annealed STFO layers induce longer exciton lifetime in the halide perovskite active layer, compared PEDOT:PSS. Similarly, the crystallization of the (PEA)2(MA)PbBr4 quasi-2D perovskite (suitable for light-emitting LED applications) on STFO layers was found to be of high quality, leading to comparable properties of layers deposited on top of classical PEDOT:PSS. Moreover, quasi-2D perovskite on STFO showed quite a long exciton lifetime. Although STFO thin films integrated into both halide perovskite PV and LED devices have conducted to limited performance, this work demonstrates the high potential of oxide perovskites towards efficient and stable all-perovskite devices
19
Wang, Yanhui. "Hybridization of lamellar oxides : from insertion to in situ synthesis." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAE037/document.
Full textAbstract:
Dans cette thèse, nous avons développé l'utilisation de l'activation microondes pour fonctionnaliser des pérovskites lamellaires et notamment la phase d'Aurivillius Bi2SrTa2O9 (BST), connue pour ses propriétés ferroélectriques. Nous sommes parvenus à protoner cette phase (HST) et à la fonctionnaliser par diverses amines et polyamines, avec des temps de réaction considérablement réduits par rapport aux fonctionnalisations en conditions classiques. Cette approche nous a permis de fonctionnaliser HST par des amines plus encombrées et plus complexes. Cette stratégie a ensuite été étendue au greffage d'alcools et de polyols. Nous avons également établi une stratégie de modification post-synthèse, pour synthétiser in situ la molécule désirée, en utilisant la chimie "click" et l'activation microondes. Enfin, nous sommes parvenus à insérer des ions métalliques et des complexes de métaux de transition, ce qui constitue une première étape vers la synthèse de nouveaux hybrides multiferroïquesDuring this PhD thesis, we have developed the use of microwave activation to functionalize layered perovskites, among which the Aurivillius phase Bi2SrTa2O9 (BST), known for its ferroelectric properties. We managed to protonate this phase (leading to HST) and to functionalize it by various amines and polyamines, with reaction times much shorter than using classical conditions. This approach allowed us to functionalize HST by bulkier and more complex amines. This strategy has further been extended to the grafting of alcohols and polyols. We have also established a postsynthesis modification strategy, in order to synthesize the desired molecule in situ, within the interlamellar space, using "click" chemistry and microwave activation. Finally, we managed to insert transition metal ions and complexes, which constitutes a promising step towards the synthesis of new multiferroic hybrid materials
20
Pesquera, Herrero David. "Strain and interface-induced charge, orbital and spin orderings in transition-me tal oxide perovskites." Doctoral thesis, Universitat Autònoma de Barcelona, 2014. http://hdl.handle.net/10803/283932.
Full text
21
Ullah, Habib. "First-principles density functional theory study of novel materials for solar energy conversion and environment applications." Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/32949.
Full textAbstract:
To design an efficient solar energy conversion device, theoretical input is extremely important to provide the basic guideline for experimental scientists, to fabricate the most efficient, cheap, and stable device with less efforts. This desire can be made possible if computational scientist use a proper theoretical protocol, design an energy material, then the experimentalist will only invest weeks or months on the synthetic effort. This thesis highlights my recent efforts in this direction. Monoclinic BiVO4 is has been using as a photocatalyst due to its stability, cheap, easily synthesizable, narrow band gap and ideal VB (-6.80 eV vs vacuum) but inappropriate CB (-4.56 eV vs vacuum) edge position, responsible for its low efficiency. We have carried out a comprehensive experimental and periodic density functional theory (DFT) simulations of the pristine, Oxygen defective (Ov), Se doped monoclinic BiVO4 and heterojunction with Selenium (Se-BiVO4), to improve not only its CB edge position but photocatalytic and charge carrier properties. It is found that Ov (1% Oxygen vacancy) and mild doped BiVO4 (1 to 2% Se) are thermodynamically stable, have ideal band edges ~ -4.30 eV), band gaps (~1.96 eV), and small effective masses of electrons and holes. We have also investigated the contribution of Se to higher performance by effecting morphology, light absorption and charge transfer properties in heterojunction. Finally, it is found that Se makes a direct Z-scheme (band alignments) with BiVO4 where the photoexcited electron of BiVO4 recombine with the VB of Se, consequences electron-hole separation at Se and BiVO4, respectively, as a result, enhanced photocurrent is obtained. Theoretical study of β-TaON in the form of primitive unit cell, supercell and its N, Ta, and O terminated surfaces are carried out with the help of periodic DFT. Optical and electronic properties of all these different species are simulated, which predict TaON as the best candidate for photocatalytic water splitting contrast to their Ta2O5 and Ta3N5 counterparts. The calculated bandgap, valence band, and conduction band edge positions predict that β-TaON should be an efficient photoanodic material. The valence band is made up of N 2p orbitals with a minor contribution from O 2p, while the conduction band is made up of Ta 5d. Turning to thin films, the valence band maximum; VBM (−6.4 eV vs. vacuum) and the conduction band minimum; CBM (−3.3 eV vs. vacuum) of (010)-O terminated surface are respectively well below and above the redox potentials of water as required for photocatalysis. Charge carriers have smaller effective masses than in the (001)-N terminated film (VBM −5.8 and CBM −3.7 eV vs. vacuum). However, due to wide band gap (3.0 eV) of (010)-O terminated surface, it cannot absorb visible wavelengths. On the other hand, the (001)-N terminated TaON thin film has a smaller band gap in the visible region (2.1 eV) but the bands are not aligned to the redox potential of water. Possibly a mixed phase material would produce an efficient photoanode for solar water splitting, where one phase performs the oxidation and the other reduction. Computational study of an optically transparent, near-infrared-absorbing low energy gap conjugated polymer, donor−acceptor−donor (D-A-D) with promising attributes for photovoltaic application is reported herein. The D and A moiety on the polymeric backbone have been found to be responsible for tuning the band gap, optical gap, open circuit (Voc) and short-circuit current density (Jsc) in the polymers solar cells (PSC). Reduction in the band gap, high charge transformation, and enhanced visible light absorption in the D-A-D system is because of strong overlapping of molecular orbitals of D and A. In addition, the enhanced planarity and weak steric hindrance between adjacent units of D-A-D, resulted in red-shifting of its onset of absorption. Finally, PSC properties of the designed D-A-D was modeled in the bulk heterojunction solar cell, which gives theoretical Voc of about 1.02 eV. DFT study has been carried out to design a new All-Solid-State dye-sensitized solar cell (SDSC), by applying a donor-acceptor conjugated polymer instead of liquid electrolyte. The typical redox mediator (I1−/I3−) is replaced with a narrow band gap, hole transporting material (HTM). A unique “upstairs” like band energy diagram is created by packing N3 between HTM and TiO2. Our theoretical simulations prove that the proposed configuration will be highly efficient as the HOMO level of HTM is 1.19 eV above the HOMO of sanitizer (dye); providing an efficient pathway for charge transfer. High short-circuit current density and power conversion efficiency is promised from the strong overlapping of molecular orbitals of HTM and sensitizer. A low reorganization energy of 0.21 eV and exciton binding energy of 0.55 eV, confirm the high efficiency of HTM. Theoretical and experimental studies of a series of four porphyrin-furan dyads were designed and synthesized, having anchoring groups, either at meso-phenyl or pyrrole-β position of a zinc porphyrin based on donor–π–acceptor (D–π–A) approach. The porphyrin macrocycle acts as donor, furan hetero cycle acts as π-spacer and either cyanoacetic acid or malonic acid group acts as acceptor. Optical bandgap, natural bonding, and molecular bonding orbital (HOMO–LUMO) analysis confirm the high efficiency pyrrole-β substituted zinc porphyrins contrast to meso-phenyl dyads. DFT study of polypyrrole-TiO2 composites has been carried out to explore their optical, electronic and charge transfer properties for the development of an efficient photocatalyst. Titanium dioxide (Ti16O32) was interacted with a range of pyrrole (Py) oligomers to predict the optimum composition of nPy-TiO2 composite with suitable band structure for efficient photocatalytic properties. The study has revealed that Py-Ti16O32 composites have narrow band gap and better visible light absorption capability compared to individual constituents. A red-shifting in λmax, narrowing band gap, and strong intermolecular interaction energy (-41 to −72 kcal/mol) of nPy-Ti16O32 composites confirm the existence of strong covalent type interactions. Electron−hole transferring phenomena are simulated with natural bonding orbital analysis where Py oligomers found as donor and Ti16O32 as an acceptor in nPy-Ti16O32 composites. Sensitivity and selectivity of polypyrrole (PPy) towards NH3, CO2 and CO have been studied at DFT. PPy oligomers are used both, in the doped (PPy+) and neutral (PPy) form, for their sensing abilities to realize the best state for gas sensing. Interaction energies and amount of charges (NBO and Mulliken charge analysis) are simulated which reveal the sensing ability of PPy towards these gases. PPy, both in doped and neutral state, is more sensitive to NH3 compared to CO2 and CO. More interestingly, NH3 causes doping of PPy and de-doping of PPy+, providing evidence that PPy/PPy+ is an excellent sensor for NH3 gas. UV-vis and UV-vis-near-IR spectra of nPy, nPy+, and nPy/nPy+-X complexes demonstrate strong interaction of PPy/PPy+ with these atmospheric gases. The applications of graphene (GR) and its derivatives in the field of composite materials for solar energy conversion, energy storage, environment purification and biosensor applications have been reviewed. The vast coverage of advancements in environmental applications of GR-based materials for photocatalytic degradation of organic pollutants, gas sensing and removal of heavy metal ions is presented. Additionally, the presences of graphene composites in the bio-sensing field have been also discussed in this review.
22
MONTEIRO, NATALIA K. "Síntese e caracterização de manganita-cromita de lantânio dopada com rutênio para anodos de células a combustível de óxidos sólidos." reponame:Repositório Institucional do IPEN, 2011. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10041.
Full textAbstract:
Made available in DSpace on 2014-10-09T12:34:06Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:00:10Z (GMT). No. of bitstreams: 0
Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
23
Abel, Stefan. "Dispositifs électro-optiques à base de titanate de baryum épitaxié sur silicium pour la photonique intégrée." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENT004/document.
Full textAbstract:
En premier lieu, des couches minces épitaxiales ont été obtenues sur des substrats de silicium grâce à l’utilisation de l’épitaxie par jets moléculaire et de couches tampons de titanate de strontium SrTiO3. Une technique de croissance par co-déposition a été développée de manière à obtenir un rapport Ba:Ti proche de la stoechiométrie, et ce afin d’éviter la formation de défauts cristallins dans la couche de BaTiO3. Le matériau déposé cristallise dans une structure de symétrie quadratique, ce qui est unpré-requis pour l’obtention de propriétés électro-optiques. De plus, selon les conditions de croissance, l’axe c de la maille élémentaire quadratique a pu être ajusté de manière à être aligné parallèlement ou perpendiculairement à la surface du substrat. L’utilisation d’une mince couche tampon de nucléation a également permis de croitre des films mincesBaTiO3 épitaxiées par pulvérisation, technique largement répandue en milieu industriel.Un coefficient de Pockels élevé a par la suite été obtenu sur de tellescouches épitaxiées. La valeur mesurée de 148pmV est clairement supérieure aux valeurs admises dans la littérature pour d’autres matériaux nonlinéairestels que le niobate de lithium, pour lequel un coefficient de31pmV est rapporté. La méthode de caractérisation électro-optique développée à cette occasion révèle également le caractère ferroélectrique des couches de BaTiO3, observé pour la première fois dans de tels matériaux épitaxiés sur silicium.Finalement, ces couches minces électro-optiquement actives ont été intégrées dans des dispositifs photoniques sur silicium. Dans cette optique,une structure de guide d’onde à fente a été utilisée en insérant 50nm deBaTiO3 entre deux couches de silicium. Dans ce type de structure, le confine mentoptique est 5 fois supérieur à celui obtenu pour des guides d’onde en silicium avec une gaine à base de BaTiO3. Des guides d’ondes rectilignesont tout d’abord été fabriqués, pour lesquels des pertes optiques del’ordre de 50−100 dB/cm ont été mesurées. Par la suite, des composants passifs fonctionnels ont été fabriqués, tels que des interféromètres typeMach-Zehnder, des résonateurs circulaires et des coupleurs. Finalement,la fonctionnalité de composants actifs a été démontrée pour la première fois, en se basant notamment sur des résonateurs ayant un facteur de qualité Q d’environ 5000, et pour lequel la résonance varie en fonction du champ électrique transverse. L’origine physique de cette variation n’a cependant pas pu être expliquée sur la seule base de l’effet Pockels. Cette thèse démontre que l’utilisation de nouveaux matériaux électro optiquement actifs au coeur de dispositifs photoniques sur silicium créede nouvelles opportunités pour la conception et l’ingénierie de circuitsphotoniques. L’intégration d’oxydes tels que barium titanate permet d’envisager de nouveaux concepts de dispositifs pour ajuster, moduler ou commuter la lumière au sein de circuits photoniques denses. De nouveaux défis et perspectives s’ouvrent également aux scientifiques pour modifier artificiellement les propriétés électro-optiques de ces matériaux, que ce soit par contrainte, dopage ou par l’ingénierie de multicouches. De telles avancées pourront sans aucun doute fortement améliorer les performances des dispositifsA novel concept of utilizing electro-optical active oxides in silicon photonic devices is developed and realized in the frame of this thesis. The integration of such oxides extends the silicon photonics platform by non-linear materials, which can be used for ultra-fast switching or low-power tuning applications. Barium titanate is used as active material as it shows one of the strongest Pockels coefficients among all oxides. Three major goals are achieved throughout this work: First, thin films of BaTiO3 are epitaxially grown on silicon substrates via molecular beam epitaxy (MBE) using thin SrTiO3 buffer layers. A shuttered co-deposition growth technique is developed in order to minimize the formation of defects in the BaTiO3 films by achieving a 1:1 stoichiometry between barium and titanium. The layers show a tetragonal symmetry and are therefore well-suited for electro-optical applications. The orientation of the long c -axis of the BaTiO3 crystal can be tuned to point perpendicular or parallel to the film surface, depending on the growth conditions. In addition, thin MBE-grown seed layers are combined with rf-sputter deposition. With this hybrid growth approach, rather thick ( > 100 nm), epitaxial BaTiO3 layers on silicon substrates are obtained with a commercially available, wide spread deposition technique. As a second goal, a strong Pockels coefficient of reff = 148 pm/V is determined in the epitaxial BaTiO3 films. This first experimental result on the electro-optical activity of BaTiO3 layers on silicon shows a clear enhancement compared to alternative non-linear materials such as lithium niobate with reff = 31 pm/V. By means of the electro-optical characterization method, also the presence of ferroelectricity in the films is demonstrated. Third, the electro-optical active BaTiO3 layers are embedded into silicon photonic devices. For this purpose, a horizontal slot-waveguide structure with a ~50 nm-thick BaTiO3 film sandwiched between two silicon layers is designed. With this design, the optical confinement in the active BaTiO3 layer is enhanced by a factor of 5 compared to Si-waveguide structures with a standard cross section and BaTiO3 as cladding. Straight BaTiO3 slot-waveguides with propagation losses of 50 − 100 dB/cm as well as functional passive devices such as Mach-Zehnder-interferometers, couplers, and ring resonators are experimentally realized. Additionally, first active ring resonators with Q-factors of Q~5000 are fabricated. The physical origin of the observed resonance shift as a function of the applied bias voltage, however, can not be conclusively clarified in the present work. The combination of high-quality, functional BaTiO3 layers with silicon photonic devices as demonstrated in this thesis offers new opportunities by extending the design palette for engineering photonic circuits with the class of electro-opticalactive materials. The integration of oxides such as BaTiO3 enables novel device concepts for tuning, switching, and modulating light in extremely dense photonic circuits. The integration also opens exciting challenges for material scientists to tailor the electro-optical properties of those oxides by strain engineering or fabrication of superlattice structures, which could ultimately lead to another boost of their electro-optical properties
24
Er-Rakho, Lahcen. "Oxydes de cuivre a valence mixte : perovskites deficitaires en oxygene." Caen, 1987. http://www.theses.fr/1987CAEN2036.
Full textAbstract:
Mise en evidence et etude de deux grandes familles de composes dans le systeme la::(2)o::(3)-ao-cuo(a=ca,ba,sr) : la::(2-x)ba::(1-x)cu::(1-x/2)o::(5-x)(ln=la,nd) ou cu est essentiellement au degre d'oxydation 2 et une seconde famille caracterisee par la valence mixte du cuivre, les quantites de cuivre 3 pouvant atteindre dans certains cas 40%. Tous ces oxydes ont en commum leur appartenance a la structure perovskite. Proprietes electriques et magnetiques
25
JUNQUEIRA, ASTROGILDO de C. "Estudo de interacoes hiperfinas em oxidos perovskitas do tipo La(MT)Osub(3) (MT=metais de transicao Fe, Cr, Mn e Co)." reponame:Repositório Institucional do IPEN, 2004. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11242.
Full textAbstract:
Made available in DSpace on 2014-10-09T12:49:51Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:03:04Z (GMT). No. of bitstreams: 1 09826.pdf: 5905522 bytes, checksum: b0354cc2f21014da9657b88019b2b992 (MD5)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
FAPESP:99/07068-0
26
REGRENY, RICARD ODILE. "Etude de la synthese et frittage d'oxynitrures de type perovskite en vue de leur application en tant que materiaux dielectriques." Rennes 1, 1988. http://www.theses.fr/1988REN10127.
Full textAbstract:
On a optimise la synthese d'oxynitrures de type abo::(2)n, de structure perovskite et presentant des caracteristiques dielectriques interessantes, afin d'obtenir des produits purs en grande quantite: batao::(2)n, srtao::(2)n, banbo::(2)n, srnbo::(2)n, ainsi que des solutions solides de ces composes. On a ensuite etudie leur densification sous atmosphere neutre ou non oxydante, avec ou sans ajouts de frittage, cherchant a obtenir une ceramique dielectrique. Une telle ceramique pourrait, utilisee comme materiau de base pour condensateurs multicouches, remplacer le batio::(3), qui doit etre cofritte avec des electrodes internes en metaux couteux
27
Lukose, Rasuole. "Liquid-delivery metal-organic chemical vapour deposition of perovskites and perovskite-like compounds." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2011. http://dx.doi.org/10.18452/16278.
Full textAbstract:
Perowskite und Perowskit-artige Materialien sind von großem Interesse, da sie eine Vielzahl von strukturellen und physikalischen Eigenschaften haben, welche die Möglichkeit bieten, sie für unterschiedliche Anwendungen einzusetzen. Die Methode der Liquid-Delivery Metal Organic Chemical Vapour Deposition (LD-MOCVD) wurde gewählt, da sie eine gute Kontrolle über die Zusammensetzung ternärer Oxide und eine hohe Homogenität der Filme ermöglicht. Darüber hinaus können mit dieser Methode Filme hergestellt werden, die aus Elementen bestehen, für welche nur feste Precursor oder welche mit niedrigem Dampfdruck zur Verfügung stehen. Ziel dieser Arbeit war es, mit Hilfe der LD-MOCVD Filme aus SrRuO3, Bi4Ti3O12 und (Na,Bi)4Ti3O12 abzuscheiden und den Einfluss der Wachstumsbedingungen auf die Eigenschaften der Filme zu untersuchen. Zusätzlich wurde die Wirkung der Verspannung, die durch die Gitterfehlanpassung zwischen Substrat und Film entsteht, auf die physikalischen Eigenschaften der Schichten untersucht. SrRuO3 Filme wurden auf gestuften SrTiO3(001), NdGaO3(110) und DyScO3(110) Substraten gewachsen, deren Oberflächenterminierung durch oberflächensensitive Proton-induzierte Auger-Elektronen-Spektroskopie (AES) bestimmt wurde. Die Substrate wurden unter verschiedenen Bedingungen durch Änderung der Temperdauer und -atmosphäre präpariert. Die systematische Untersuchung der Beziehung zwischen Verspannung und Curie-Temperatur von dünnen SrRuO3(100) Filmen erfolgte unter Verwendung von Substraten mit unterschiedlichen Gitterkonstanten. Die beobachtete Curie-Temperatur sank mit erhöhter kompressiver Verspannung und nahm mit erhöhter tensiler Verspannung zu. Um stöchiometrische und epitaktische Bi4Ti3O12(001) Filme zu wachsen, war aufgrund der Flüchtigkeit des Bismuts ein Bi Überschuss in der Precursor-Lösung notwendig. Die Substitution von Bi durch Na in Bi4Ti3O12 wurde zum ersten Mal in LD-MOCVD-Filmen erreicht.Perovskites and perovskite-like materials are actually of great interest since they offer a wide range of structural and physical properties giving the opportunity to employ these materials for different applications. Liquid-Delivery Metal Organic Chemical Vapour deposition (LD-MOCVD) was chosen due to the easy composition control for ternary oxides, high uniformity and good conformal step coverage. Additionally, it allows growing the films, containing elements, for which only solid or low vapour pressure precursors, having mainly thermal stability problems over long heating periods, are available. The purpose of this work was to grow SrRuO3, Bi4Ti3O12 and (Na, Bi)4Ti3O12 films by LD-MOCVD and to investigate the influence of the deposition conditions on the properties of the films. Additionally, the effect of the strain due to the lattice mismatch between substrates and films on the physical properties of the films was also investigated. SrRuO3 films were grown on stepped SrTiO3(001), NdGaO3(110) and DyScO3(110) substrates, which were prepared under different conditions by changing the annealing time and atmosphere. The termination of the substrates was measured by surface sensitive proton-induced Auger Electron Spectroscopy (p-AES) technique. Another systematic study of the relation between epitaxial strain and Curie temperature of thin SrRuO3(100) films was performed by using substrates with different lattice constants. The observed Curie temperature decreased with compressive and increased with tensile strain. Thin films of Bi4Ti3O12 as well as (Na, Bi)4Ti3O12 were successfully deposited. In order to grow stoichiometric and epitaxial Bi4Ti3O12(001) films, Bi excess in the precursor solution was necessary, due to the volatility of Bi. Substitution of Bi with Na in Bi4Ti3O12 was achieved for the first time for the films deposited by LD-MOCVD.
28
Copplestone, Francis A. "Catalytic studies of perovskite oxides." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358591.
Full text
29
Baskar, Dinesh. "High temperature magnetic properties of transition metal oxides with perovskite structure /." Thesis, Connect to this title online; UW restricted, 2008. http://hdl.handle.net/1773/9812.
Full text
30
Logvinovich, Dmitry. "Anionic substitution in perovskite-type oxides." kostenfrei, 2008. http://d-nb.info/993937535/34.
Full text
31
Ovalle, Alejandro. "Manganese titanium perovskites as anodes for solid oxide fuel cells." Thesis, St Andrews, 2008. http://hdl.handle.net/10023/567.
Full text
32
Ren, Xiaolin. "Synthesis and characterisation of metal oxides and fluorinated perovskite-related oxides." Thesis, Open University, 2005. http://oro.open.ac.uk/54200/.
Full textAbstract:
Perovskite-related materials of composition LaFe1-xCoxO3 prepared by conventional calcination methods and mechanical milling are shown by temperature programmed reduction to be more susceptible to reduction in a flowing mixture of hydrogen and nitrogen by the incorporation of cobalt. X-ray powder diffraction and Mossbauer spectroscopy show that in iron-rich systems the limited reduction of iron and cobalt leads to the segregation of discrete metallic phases without destruction of the perovskite structure. In cobalt-rich systems, the reduction of Co3+ to Coo precedes complete reduction of Fe3+ and the segregation of alloy and metal phases is accompanied by destruction of the perovskite structure. Phases made by milling techniques were of smaller particle size and are more susceptible to hydrogen reduction than their counterparts made by conventional techniques. Materials of the type La0.5Sr0.5MO3 (M= Fe, Co) made by calcination methods are more susceptible to reduction when the transition metal M is cobalt as compared to iron. Perovskite-related oxides of composition La1-xSrxFe1-yCoyO3 have been fluorinated by reaction with poly(vinylidene fluoride). The materials have been characterised by X-ray powder diffraction and Mossbauer spectroscopy. Fluorination induces a reduction in the oxidation state of iron from Fe4+ to Fe3+. The fluorinated materials were magnetically ordered at 298 K. Compounds of the type SrFe1-xSnxO3 were found to contain Fe5+ and Fe3+. Fluorination resulted in reduction of the transition metal to Fe3+ and, in iron-rich systems, magnetic order. The compound Ba2SnO4 which adopts the K2NiF4-type structure has also been fluorinated by reaction with zinc fluoride. X-ray powder diffraction shows an enlargement of the unit cell of the fluorinated phase along the c-axis. Small particle iron- and vanadium- antimonate have been prepared by mechanical milling methods. The phases have been examined by M6ssbauer spectroscopy and can be formulated M3+Sb5+O4 (M = Fe, V). Thermal analysis suggests that the vanadium animonate formed by milling V2O5 and Sb2O3 in an inert atmosphere may be oxygen deficient. X-ray powder diffraction shows that milling also induces the phase transformation of the cubic senarmontite Sb2O3 form to the orthorhombic valentinite Sb2O3 form and of a-Sb2O4 to B-Sb2O4.
33
Noailles, Liam Dagme. "Chemistry and properties of complex Perovskite oxides." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249440.
Full text
34
Hassler, Julia. "Mesoporous metal oxides for perovskite solar cells." Thesis, Uppsala universitet, Molekyl- och kondenserade materiens fysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-263064.
Full text
35
Kirk, Caroline A. "Crystal chemistry of novel perovskite-related oxides." Thesis, University of Aberdeen, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.481799.
Full text
36
Allieta, M. "DIFFRACTION STUDIES ON STRONGLY CORRELATED PEROVSKITE OXIDES." Doctoral thesis, Università degli Studi di Milano, 2012. http://hdl.handle.net/2434/168362.
Full textAbstract:
In recent years, a great interest has been devoted to the so called strongly correlated systems containing perovskite building blocks. These systems exhibit a complex interplay between charge, spin, orbital and lattice degrees of freedom paving the way for very attractive applications.
In this work, entitled “Diffraction Studies on Strongly Correlated Perovskite Oxides” the use of x-ray diffraction techniques to investigate the coupling between the structure and the physical properties of several bulk material based on perovskite structure is presented.
The thesis is organized in five chapters. Introduction presents a very general overview on strongly correlated perovskite oxides and the scope of the thesis. The first chapter reports technical details of the diffraction techniques involved in all the structural studies performed during the PhD.
Chapter 2 reports an accurate investigation performed on the magnetoresistive cobaltite GdBaCo2O5+d (d=0) using single-crystal and synchrotron powder X-ray diffraction. In this work, we assign the correct space group and we demonstrate that a very small tetragonal-to-orthorhombic lattice distortion is coupled to magnetic phase transition. In Chapter 3, we show the study of the temperature induced insulator-to-metal transition for GdBaCo2O5+d (d>0.5). By using a combined approach between electron paramagnetic resonance and powder diffraction techniques we provide new interesting features about the spin – lattice interaction occurring in these systems. Chapter 4 presents synchrotron X-ray powder diffraction study on EuTiO3 system. We show for the first time the existence of a new structural phase transition occurring in EuTiO3 below room temperature. In addition, by performing the atomic pair distribution function analysis of the powder diffraction data, we provide evidence of a mismatch between the local (short-range) and the average crystallographic structures in this material and we propose that the lattice disorder is of fundamental importance to understand the EuTiO3 properties. Finally, beyond the scope of the thesis, in Chapter 5, we review the basic procedure to get the differential pair distribution function obtained by applying the anomalous X-ray diffraction technique to total X- ray scattering method. We show an example of the application of this procedure by presenting the case of gadolinium doped ceria electrolytes.
This work will show that use of the powder diffraction techniques provides a powerful tool to unveil the coupling between the structure and the physical properties in strongly correlated perovskite oxides.
37
Moore, Caroline A. "Synthesis and characterisation of low-dimensional oxides." Thesis, University of Oxford, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289407.
Full text
38
Raisch, Christoph Werner [Verfasser], and Thomas [Akademischer Betreuer] Chassé. "Investigations of the electronic, magnetic and crystalline structure of perovskite oxides and an oxide-oxide interface / Christoph Werner Raisch ; Betreuer: Thomas Chassé." Tübingen : Universitätsbibliothek Tübingen, 2013. http://d-nb.info/1162844124/34.
Full text
39
Shaw, Cynthia Kit Man. "Mass transport in mixed conducting perovskite related oxides." Thesis, Imperial College London, 2001. http://hdl.handle.net/10044/1/8380.
Full text
40
Xu, Xiaomin. "Engineering of Perovskite Oxides for Electrochemical Water Splitting." Thesis, Curtin University, 2020. http://hdl.handle.net/20.500.11937/82587.
Full textAbstract:
While electrochemical water splitting offers an alluring prospect of carbon-neutral H₂ production from renewable resources, its efficiency is limited by the slow kinetics of the anodic/cathodic half-reactions. This thesis centres on the engineering of non-precious metal-based perovskite oxides as electrocatalysts to drive the water electrolysis. By fine-tuning the chemical compositions and structures, perovskite oxides with improved catalytic efficiency are developed. A deepened understanding of the structure–activity relationship of the perovskite electrocatalysts is also provided.
41
Wang, Jianfeng, and 王建峰. "Field modulation on transport properties in heterostructures composed of perovskite oxides." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B47147076.
Full text
42
Akizuki, Yasuhide. "High-Pressure Synthesis and Properties of Novel Perovskite Oxides." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199319.
Full text
43
Kususe, Yoshiro. "Synthesis, Structure, and Properties of Eu2+-containing Perovskite Oxides." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199320.
Full text
44
Bos, J. W. G. "Synthesis, structures and properties of new double perovskite oxides." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596791.
Full textAbstract:
Double perovskite oxides have attracted much interest since the discovery of spin-polarized conduction and large low field magnetoresistances in Sr2FeMoO6. This behaviour exists to high temperatures, making Sr2FeMoO6 and related materials candidates for application in data storage devices. This thesis describes the synthesis, structures and properties of some new double perovskite oxides. These can be divided into the (LaM)BNbO6 (M = Ca, Sr, Ba; B = Mn, Co) and LaSrFeNbO6 materials that have one magnetic transition metal (TM) cation, and the (La1+xM1-x)CoRuO6 (M = Ca, Sr; -0.25 £ x £ 0.25 x = 1) materials that have two magnetic TM cations. The (LaM)CoNbO6 double perovskites crystalize with the monoclinic P21/2 (M = Ca, Sr) and tetragonal 14/m (M = Ba) superstructures, which have rocksalt ordered arrangements of Co2+ (3d7) and Nb5+ (4d0), with almost no Co/Nb inversion (<4%). All three phases are anti-ferromagnetic with Neel temperatures of 17 K (M = Ca), 16 K (M = Sr) and 10K (M = Ba). The magnetic ordering is described by the magnetic propagation vector k = ( ½ 0 ½ ) for all materials. For M = Ca and Sr, two “non-collinear” and two “collinear” magnetic structures are found. These are experimentally indeterminate because of the small monoclinic angle (b = 89.90). The M = Ba material has a collinear antiparallel magnetic structure. The saturated cobalt moment decreases from 2.97(2) mB to 2.52 (3) mB to 1.85 (5) mB for M = Ca, Sr and Ba, respectively. The frustration due to competing 900 exchange interactions. The (LaK)MnNbO6 materials also have the monoclinic P21/n (M = Ca, Sr) and tetragonal 14/m (M = Ba) superstructures, with <3% inversion of Mn2+ (3d5) and Nb5+ (4d0). All materials are antiferromagnetic with Neel temperatures of 9 K (M = Ca), 8 K (M = Ba) and 6.5 K (M = Ba). The magnetic Bragg reflections are indexed by k = (0 ½ ½ ), and the possible magnetic models are identical to those for (LaM)CoNbO6. The manganese saturation moment decreases from 4.77(3) mB (M = Ca) to 4.43 (4) mB (M = Sr) to 41.9 (4) mB (M = Ba). (LaSr)FeNbO6 has the monoclinic P21/n superstructure with 14% inversion of Fe2+ (3d6) and Nb5+ (4d0). This material is antiferromagnetic (TN = 22 K), and has a ( ½ 0 ½) magnetic propagation vector (mFe = 3.45(3) mB). The lattice parameters, antisite disorder, Neel temperatures and resistivities of the (La1-xM1-x)CoRuO6 double perovskites are found to vary in a systematic manner. The Co/Ru antisite disorder is minimal for x = 0, showing that this disorder is driven by the mixed Co or Ru electronic states at x ≠ 0 rather than by La/M cation mixing. The x = 0 materials have TN = 96K (M = Ca) and TN = 85 K (M = Sr), and are variable range hopping semiconductors. Hole doping )x < 0) results in a rapid reduction in the resistivity while the Neel temperature increases only moderately, whereas electron doping (x > 0) results in a significant reduction in TN but has little effect on the resistivity. X-ray absorption near edge spectroscopy shows that for x < 0, the Co2+ states are selectively hope doped while for x > 0 only the Ru5+ states are electron doped, which is in keeping with the strongly asymmetric doping response.
45
El-Shinawi, Hany Zakaria Ibrahim. "Synthesis and characterization of cobalt-containing perovskite-type oxides." Thesis, University of Birmingham, 2010. http://etheses.bham.ac.uk//id/eprint/625/.
Full textAbstract:
A number of cobalt-containing perovskite-type oxides were synthesized and characterized in this study. All materials were half-doped with cobalt in their B-sites, i.e. contain the Co0.5M0.5 B-site state where M = Fe, Mn, Cr, Ni; the materials adopted single layered, double-layered and simple perovskite-type structures. The materials La2 xSrxCo0.5M0.5O4 (M = Fe, Cr) have shown enhanced stability under reducing conditions (10% H2/N2, up to 1000 ºC) with the formation of oxygen deficient compounds, while no evidence for oxygen hyperstoichiometry was observed under oxidizing conditions. Materials such La1.2Sr0.8Co0.5Mn0.5O4.1 and La1.7Sr0.3Co0.5Ni0.5O4.08, however, exhibit oxygen hyperstoichiometry under oxidizing conditions and also withstand reducing conditions via formation of oxygen deficiency. Oxygen vacancies were disordered and confined to the equatorial planes of the single layered structure in all materials, while oxygen hyperstoichiometry was accommodated in the interstitial (0, 0 .5, 0.25) sites of the tetragonal structure. In La1+xSr2 xCoMnO7-δ, oxygen vacancies were confined to the common apex of the double layered structure. The new brownmillerite phase LaSrCoFeO5 was synthesized and fluorination produced the new oxyfluoride LaSrCoFeO5F. Magnetic interactions between Co2+(3+) ions and ions such as Fe3+, Mn3+, Cr3+, Ni2+ in different perovskite-type structures were also studied and a range of magnetically ordered materials, at low and room temperatures, were investigated.
46
Choi, Minseok. "Defect physics of perovskite oxides by first principles calculations." 京都大学 (Kyoto University), 2011. http://hdl.handle.net/2433/142174.
Full text
47
Lombardo, Pierre. "Théorie de champ moyen dynamique appliquée à l'étude des propriétés électroniques des oxydes de métaux de transition." Université Joseph Fourier (Grenoble ; 1971-2015), 1997. http://www.theses.fr/1997GRE10161.
Full textAbstract:
Nous avons propose une approche susceptible d'expliquer de nombreuses proprietes electroniques des materiaux dont les porteurs de charge sont soumis a de fortes correlations. Parmi les materiaux consideres, citons en particulier les supraconducteurs a haute temperature critique et les oxydes de metaux de transition de type perovskite. L'approche developpee dans cette these est une extension de la theorie de champ moyen dynamique a des systemes electroniques a plus de un degre de liberte orbital. Elle est basee sur une nouvelle procedure de renormalisation du modele de hubbard a deux bandes pour l'extension aux grandes dimensions spatiales de la structure perovskite. Un traitement selectif des differents processus de sauts entre sites de metal de transition (mt) et d'oxygene (o) plus proche voisins, nous a permis de conserver de nombreux aspects dynamiques non triviaux dans cette limite. Le probleme sur reseau est projete sur un modele d'impurete de type anderson. La solution du probleme local a ete obtenue par la theorie des perturbations iterees et par une extension de l'approximation de non-crossing (nca). La technique de nca nous a permis de decrire correctement d'importantes proprietes spectrales des oxydes de metaux de transition, donnant des informations tres interessantes sur la nature des differentes bandes des densites d'etats du metal de transition et de l'oxygene, et sur leur comportement en fonction du dopage. De plus, le pic coherent de quasiparticule, proche du niveau de fermi, a ete obtenu. Ce pic presente d'interessantes variations en fonction du dopage, mais aussi de la temperature. Ces excitations de basse energie proviennent de resonances de type kondo, entre l'etat vide et un etat hybride mt-o dans le cas du dopage en electrons, et entre cet etat mt-o et un etat singulet de type zhang et rice dans le cas du dopage en trous. L'application de notre approche nca a des familles de materiaux reels comme lamo#3 ou ca#1##xsr#xvo#3 a mis en evidence l'importance fondamentale des excitations a transfert de charge dans ces composes. Une description correcte des proprietes electroniques des oxydes de metaux de transition peut donc etre donnee par une approche de champ moyen dynamique mais necessite la prise en compte a la fois des etats de l'oxygene et de ceux du metal de transition.
48
Hopper, Harriet A. "An investigation of the structure and properties of 4d transition metal perovskite oxides." Thesis, University of Aberdeen, 2017. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=232235.
Full textAbstract:
Perovskite-type materials have been widely studied in the literature as a result of the plethora of properties they have been found to exhibit. This is largely down to their versatile nature, which allows the substitution of a wide variety of different elements into the crystallographic sites. In addition to this the presence of 4d and 5d transition metal elements enables an even wider range of potential properties to be considered. The solid solution Sr1-xBaxMoO3 (x = 0.000, 0.025, 0.050, 0.075, 0.100 and 1.000) has been synthesised. Examination of the X-ray diffraction data via Rietveld refinement showed the materials crystallised with cubic Pm-3m symmetry, and there was a miscibility gap from x = 0.1 – 1.0. Examination of the optical properties showed that increasing x from 0 to 1 reduced the measured band gap, which was attributed to the electronic transition from the Mo 4d t2g band to the eg band, from 2.20 eV to 2.07 eV, as the ligand field splitting energy is closely related to the extent of hybridisation between Mo dx2-y2 and dz2 and the O 2p orbitals and the larger radius of Ba2+ compared to Sr2+ leads to longer Mo-O bonds and therefore weaker orbital mixing. The materials were examined as potential water-splitting photocatalysts but no evidence of hydrogen or oxygen evolution was found. In a similar fashion the solid solution Sr1-xCaxMoO3 (x = 0.00, 0.05, 0.10, 0.13, 0.15 and 0.17) was synthesised, and structural phase transitions were found to occur as x increased, from cubic Pm-3m to tetragonal I4/mcm to orthorhombic Imma. Discontinuities were observed in the cell parameters, bond lengths and angles at the transition from tetragonal to orthorhombic as a result of the switching of the octahedral rotation axis at the tetragonal to orthorhombic transition. The band gap was also found to decrease from 2.20 eV to 2.10 eV as x increased, which was further attributed to the octahedral tilting. The magnetic, electrical and structural properties of the Ruddlesden-Popper material – a variation on the perovskite structure – Sr3CoRuO7 were examined, and showed no structural changes down to 5 K, and no evidence of long-range magnetic order. A broad antiferromagnetic transition was observed at ~160 K which was attributed to short-range magnetism. The material was found to be semiconducting, and displayed Mott variable-range hopping behaviour below 240 K. The novel hexagonal perovskite series Ba3AMo2O9 (A = Sr, Ca, Nd and Pr0.5Nd0.5) was successfully synthesised, and attempts were made to synthesise the material Ba4Mo2O9, which was obtained mostly phase pure, with some minor impurities which were identified as polymorphs of the material and small amounts of Ba6Nb3O13.5 and Ba5.75Nb2.25O11.38. Examination of the magnetic properties revealed what appeared to be a transition at ~100 K in the Ba4Mo2O9, Ba3SrMo2O9 and Ba3CaMo2O9 materials, and spin gap formation was suspected below 100 K. The reduction in susceptibility was a possible indicator of spin dimer formation. Curie-Weiss fits were obtained for Ba4Mo2O9, Ba3CaMo2O9 and Ba3Pr0.5Nd0.5Mo2O9.
49
Williams, Anthony James. "Synthesis and neutron diffraction studies of manganese oxide perovskites." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615786.
Full text
50
Rodríguez-Martínez, Lide Mercedes. "The effects of cation disorder in manganese oxide perovskites." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624354.
Full text