The diploma thesis deals with the study of perovskite solar cells with a regular n-i-p architecture. The theoretical part of this work is mainly focused on the stability of perovskite solar cells, i.e. thermal stability and the influence of UV radiation on final perovskite solar cell stability. Furthermore, the deposition methods, the architecture of solar cells and the materials used for the preparation of electron and hole transport layers were described in more detail. The experimental part deals with the optimization of the preparation of perovskite solar cells (especially in terms of resulting photovoltaic conversion efficiency), with a description of the structure preparation process of the final photovoltaic cell and the interpretation of the measured results.

<p>A series of layered perovskite-based compounds were synthesized and studied as follows.</p> <p>La₅Mo_2.76(4)V_1.25(4)O₁₆ is a new pillared-perovskite synthesized by solid state chemistry method. It has layers of corner-sharing octahedra separated by dimers of edge-sharing octahedra, and is the first Mo-based pillared-perovskite whose magnetic structure was determined by neutron diffraction.</p> <p>Ca₂FeMnO₅ is an oxygen-deficient-perovskite with a brownmillerite-type ordering of oxygen vacancies, resulting in layers of corner-sharing octahedra separated by chains of corner-sharing tetrahedra. The octahedral layer contains mostly (~87%) Mn, while the tetrahedral layer is mainly (~91%) occupied by Fe. Long-range G-type magnetic ordering is present, where the moment on each site is coupled antiferromagnetically relative to all nearest neighbors.</p> <p>Ca₂FeCoO₅ has a brownmillerite superstructure with space group <em>Pcmb</em>, a rare space group for brownmillerites that requires doubling of one unit cell axis. Ca₂FeCoO₅is the first brownmillerite to contain intra-layer cation ordering. It has a long-range G-type ordering, and is the first brownmillerite to show spin re-orientation as function of temperature.</p> <p>Sr₂FeMnO_5+y was synthesized in both air (y~0.5) and argon (y~0), both of which resulted in vacancy-disordered cubic structures. The argon compound has a local brownmillerite structure, i.e. local ordering of vacancies. It has a superparamagnetic state below ~55K, with domains of short range (50Å) G-type ordering at 4K. For the air synthesized compound, y~0.5, long range G-type ordering is observed in ~4% of the sample.</p> <p>Sr₂Fe_1.9M_0.1O_5+y (M=Mn, Cr, Co; y= 0, 0.5) were synthesized in both air(y~0.5), and argon(y~0). All argon materials are brownmillerites with G-type magnetic ordering, but T_N’s are significantly different. The air-synthesized Co-material has long range vacancy ordering and magnetic ordering, while the Mn and Cr-materials (air) lack such orderings and both show spin-glass-like transitions.</p> <p>Sr₂Fe_1.5Cr_0.5O₅ has a vacancy-disordered cubic structure, but contains long range G-type magnetic ordering, unlike the other vacancy-disordered materials studied.</p> / Doctor of Philosophy (PhD)

The group of materials with ABO3 type perovskite structure are very important due to their attractive electrical and magnetic properties for technological applications and have been studied in the form of single crystals, bulk polycrystalline materials and thin films. Recently, efforts have been made to synthesize and understand the growth of ABO3 type perovskite nanostructures because of their distinctive physical properties and potential applications in the nanodevices. The primary aim of the present thesis is to synthesize the perovskites at nano-scale, with zero-dimension (0D), and one-dimension (1D) configurations. Basic work was carried in terms of synthesis – structure – composition correlation. Due to the small nature of the synthesized materials, few attempts were done to examine the physical properties, but to a limited extant. Efforts were also done to emphasize the structural behavior of nano perovskite in comparison with their bulk counterparts. Chapter 1 provides a brief introduction to perovskite materials and nanostructures, their technological applications and the fundamental physics involved. A brief review of the perovskite nanostructures both from fundamental science and technological point of view is provided. Finally the specific objectives of the current research are outlined. Chapter 2 deals with the experimental studies carried out in this thesis. It describes the methods used for the synthesis, experimental set up and the basic operation principles of various structural and physical characterizations such as X-ray diffraction (XRD), thermal analysis, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), compositional analysis (EDX), focused ion beam (FIB), electrical and magnetic studies of the materials prepared. Chapter 3 describes the fabrication of porous anodic aluminum oxide (AAO) templates with different pore size, basic steps for synthesis of nanotubes and the possible growth mechanism of nanotubes in the AAO template. In chapter 4, we report the synthesis of ferroelectric Ba1-xSrxTiO3 (x = 0.0, 0.3) nanoparticles (diameter range: 20-40nm) and Ba1-xSrxTiO3 (x = 0.0, 0.4) nanotubes with diameter about 200nm by the sol-gel method. The Ba1-xSrxTiO3 nanostructures so obtained were characterized by number of techniques, including FE-SEM, XRD, DTA/TGA, FTIR spectroscopy, TEM, HRTEM as well as EDX and SAED. Formation of Y-junctions and multi-branches in Ba1-xSrxTiO3 nanotubes were also observed. The wall of the nanotubes were found to be made of randomly oriented nanoparticles which were confirmed from the HRTEM image. The average thickness of the wall of the nanotubes was found around 15(±5) nm and nanoparticles consisting the wall were found to be in the range of 5-10nm. Diffused phase transition (cubic to tetragonal), shifted to lower temperature side and leaky ferroelectric P–E loops were observed in Ba1-xSrxTiO3 (x = 0.0) ceramic prepared from nanoparticles. Curie temperature was observed at 120oC in the BT nanotube array as confirmed by the dielectric study. The P–E loops of as-prepared Ba1-xSrxTiO3 (x = 0.0) nanotube array were also measured and the hysteresis clearly demonstrates the room temperature ferroelectricity in the as prepared nanotubes, indicating these nanotube array is potential media as ferroelectric information storage. In chapter 5, we report the synthesis of single crystalline nanoparticles and polycrystalline nanotubes of Pb0.76Ca0.24TiO3 (PCT24) by sol-gel processing and characterized by various techniques. The crystallinity and phase purity of the PCT24 nanoparticles and nanotubes were confirmed by the XRD and SAED pattern. Compositional homogeneity and their crystalline structure confirms the formation of the tetragonal perovskite phase. The wall of the nanotubes was found to be made of nanoparticles which were confirmed from the HRTEM analysis. The average thickness of the wall of the nanotubes was found around 20nm and nanoparticles consisting the wall were found to be in the range of 5-8nm. Formation of some single crystalline PCT24 nanorods was also observed as confirmed by SAED and HRTEM analysis. Formations of Y-junctions and multi-branches in this complex functional oxide were observed. Dielectric measurements shows the diffuse phase transition and frequency dependence of Tm (temperature at which real part of dielectric constant shows maxima) suggesting the relaxor type behavior in the PCT24 ceramic prepared from nanoparticles. Polarization study was carried out on PCT24 nanotube array, which shows the ferroelectric nature at room temperature. Chapter 6 reports the synthesis and studies of PbZrO3 (PZ) nanoparticles and PbZr1-xTixO3 for x = 0.0, 0.48 and 1.0 nanotubes. PZ nanoparticles were prepared by a novel sol-gel method based on diol-based solution. Initially, PZ was crystallized with some intermediate m-Z and t-Z phases at 400-550oC and start transforming to orthorhombic at around 600oC and then finally transformed into pure orthorhombic PZ phase at about 700oC. XRD and TEM confirmed the nanocrystalline nature of PZ particles. Curie temperature in the PZ ceramic prepared from PZ nanoparticles was observed around at 205oC, which is lower as compared to the bulk (233oC). P–E hysteresis loops of PZ ceramic prepared from nanoparticles were measured at different applied voltages and single ferroelectric loops of leaky nature were observed rather than antiferroelectrics. The lead zirconate nanoparticles produced may have potential applications as materials used in microelectronics and microelectromechanical systems. PbZr1-xTixO3 for x = 0.0 (PZ), 0.48 (PZT48) and 1 (PT) nanotubes were fabricated by sol-gel method within the closely packed porous alumina templates and characterized by various techniques. The crystallinity of the PZ, PZT48 and PT nanotubes were confirmed via XRD and SAED studies. EDX analysis demonstrated that stoichiometry was formed. Formation of Y-junctions in this complex functional oxide was also observed. The wall of the nanotubes was found to be made up of randomly oriented nanoparticles, which were confirmed by the HRTEM studies and also by a typical SEM image. The average thickness of the wall of the nanotubes was found to be around 10-20nm and nanoparticles consisting the wall was found to be in the range of 3 – 8nm. The Curie temperature was observed at 220oC in the PZ nanotube array. For the first time, PLD has been employed for the synthesis of lead zirconate nanotubes using AAO template. Well-registered arrays of these nanotubes could function as three dimensional (3D) device elements in miniaturized ferroelectric random access memory (FRAM). In chapter 7, we report the synthesis of single crystalline 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 (PMN-PT) nanoparticles. PMN-PT nanoparticles were developed by a novel sol-gel method based on diol route. After partial calcination at 450oC/1h, PMN-PT powder morphology started transforming from pyrochlore to perovskite phase. It is interesting to note that this partially crystallized PMN-PT powder was unstable under electron beam and generated freestanding lead nanoparticles after absorbing energy from a focused electron beam. PMN-PT powder annealed at 700°C was fully transformed to perovskite phase and was stable under electron beam. XRD calculations and TEM imaging confirmed the nanocrystalline nature of PMN-PT particles. Magnetic measurements on PMN-PT nanoparticles prepared at 650 and 750oC show room temperature ferromagnetic hysteresis, whereas the bulk or the agglomerated particles show diamagnetic behavior. With an increase of annealing temperature or the particle size the magnetic moment decreases. PMN-PT nanotubes with diameter about 200nm were fabricated successfully by the sol-gel method based on diol route within the closely packed porous nanochannel alumina templates. Phase purity and crystalline perovskite phase formation of PMN-PT nanotubes were confirmed by the XRD and SAED pattern. EDX analysis demonstrated that stoichiometry was formed within accepted limit. The wall of the nanotubes was found to be made of nanoparticles which were confirmed from the HRTEM analysis. The average thickness of the wall of the nanotube was found around 20 nm and nanoparticles consisting the wall were found to be in the range of 10-20 nm. Since electroceramic materials are following a similar trend to miniaturization as conventional semiconductors, the synthesis of nanosized oxidic building blocks is moving into the focus of scientific and technological interest. Ferroelectrics are promising class of materials for the fabrication of electronic devices, as they are already an integral part of modern nanotechnological operations. Chapter 8 deals with the synthesis and properties of BiFeO3 (BFO) nanoparticles and nanotubes. Single crystalline BFO nanoparticles of different size and polycrystalline BFO nanotubes were prepared by sol-gel method. As prepared nanostructures were characterized by various techniques such as XRD, TGA-DTA, FTIR, scanning electron microscope (SEM), transmission electron microscope (TEM), selected-area electron diffraction (SAED), high resolution TEM and energy-dispersive X-ray spectroscopy (EDX). The crystallinity and phase purity of the BFO nanoparticles and nanotubes were confirmed by the XRD, SAED pattern and HRTEM analysis. Compositional homogeneity and their crystalline structure confirms the formation of the rhombohedrally distorted perovskite phase. EDX analysis demonstrated that stoichiometric BiFeO3 was formed within accepted limit. The HRTEM analysis confirmed that wall of the BFO nanotubes was made of nanoparticles, which were randomly oriented in the wall. The average thickness of the wall of the nanotubes was found to be around 15 nm and nanoparticles consisting the wall were found to be in the range of 3-6nm. Formation of Y-junctions in this complex functional oxide was observed. Magnetic measurements show clearly the enhancement of ferromagnetism in BFO nanotubes and ferroelectric loops were also observed in these nanotubes, that indicates the multiferroic nature of these nanotubes. BFO nanostructures at a large scale might be important for many applications such as memory elements in nanoscale devices in future. Chapter 9 reports the synthesis of a series of crystalline La1-xCaxMnO3 (x = 0, 0.3, 0.5, 0.7) nanoparticles with average diameter about 20 nm by an improved sol-gel method. The crystallinity and phase formation of as prepared nanoparticles was confirmed via XRD, SAED and HRTEM studies. EDX analysis demonstrated that desired stoichiometric was formed. Magnetic characterization reveals that the PM-FM transitions (Tc) occurs around at 205, 235, 235 and 230 K for x = 0, 0.3, 0.5, 0.7, respectively. The strong irreversibility between zero field cooling (ZFC) and field cooling (FC) magnetization curves, a cusplike peak in ZFC curve and unusual shape of M versus H loop at T = 5 K gives strong support for surface spin glass behavior. The highly stable charge ordering state in bulk manganites is suppressed, while the ferromagnetism is enhanced in these nanoparticles (x = 0.5 and 0.7). La0.7Ca0.3MnO3 were fabricated by sol-gel method within the closely packed porous alumina templates. The wall of the nanotubes was found to be made up of randomly oriented nanoparticles (8-12nm) as confirmed by HRTEM studies. The strong irreversibility between ZFC and FC magnetization curves as well as a cusplike peak in ZFC curve gives strong support for surface spin glass behavior. Magnetization value as obtained from M-H loop was about 28.5% of expected value, suggesting the existence of a magnetic dead layer, which avoids the propagation of exchange interaction between magnetic grains. The PM-FM transition was observed at 235 K. Chapter 10 gives the summary and conclusions of the present study and also discusses the possible future work that could after more insights into the understanding of the perovskite nanostructures. Highlight of the present work (i) Successful growth of nanostructures in both particles and tube forms, and study of their structure – composition correlations. (ii) Present work could optimize the necessary chemistry to successfully grow nanoparticles and nanotubes of various perovskite compositions. (iii) Successful studies of physical properties of nanoparticles and nanotubes, ofcourse, to a limited extent. However the properties observed in the present nanostructures have a strong indication of nonlinear phenomena similar to their bulk counterparts. (iv) It was reported in the literature, the observation of ferromagnetic behavior in several nonmagnetic compositions at nano-scale. Surprisingly, similar ferroelectric behavior was noticed even in our perovskite complex oxides such as relaxors (PMN-PT). A clear interaction of magnetic spin and an electric dipole was evident in these oxides such as relaxors and also multiferroics at nano-scale (~10-20 nm). (v) In ferromagnetic compositions such as LCMO, a very interesting spin-glass type behavior was observed.

No description available.

The research presented is based on alternative anode materials for high temperature steam electrolysis. The key to commercially viable renewable energy economy is based on energy storage of intermittent sources. Hydrogen is the preferred form of energy storage for solid oxide electrolysis cells. However, conventional anode material lanthanum strontium manganite (LSM), suffers from poor ionic conductivity, thus prohibiting much of the bulk electrode from providing an enhanced electrochemical performance. This study explores the use of a double-layered perovskite system with mixed electronic and ionic conductivity for use as anode material. Specifically, the SmBa₁₋ₓSrₓCo₂O[sub](5+δ) system (SBSCO) is analyzed for characteristics that may enhance the performance and feasibility of SBSCO as an alternative anode material to LSM. Previous in-house work showed SmBa₀.₅Sr₀.₅Co₂O[sub](5+δ) had the lowest area specific resistance of any double- layered material reported. Here the system is further explored by studying the full range of compositions. From X-ray diffraction analysis, increased Sr substitution leads to a tetragonal phase change in SBSCO. High temperature x-ray diffraction of compositions showed thermal stability of structure. Magnetization measurements are reported for selected compositions. The stability of SBSCO was examined in CO₂ containing atmospheres. Despite containing alkaline earth metals, the system offers limited CO₂ tolerance. A set of thermodynamic parameters is presented based on CO₂ partial pressure and temperature. Model indicates SBSCO is a stable electrode material for both electrolysis and fuel cell modes. Compositions were tested for steam electrolysis performance with the use of YSZ electrolyte, and Ni-YSZ and La₀.₄Sr₀.₄Ni₀.₀₆Ti₀.₉₄O₂.₉₄ cathodes. SmBa₀.₃Sr₀.₇Co₂O[sub](5+δ) had the highest performance for compositions (0≤x≤1) based on I-V curves and impedance measurements. Stability tests were conducted in potentiostatic mode and no delamination was observed for SBSCO in microstructural analysis after testing. From these studies, SBSCO is demonstrated to be a suitable for application in electrolysis and an alternative for LSM as anode material.

by Tsai Yau Moon = 錳氧化物的金屬-絶緣體轉變 : 多層薄膜及異構結 / 蔡友滿. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / by Tsai Yau Moon = Meng yang hua wu de jin shu-jue yuan ti zhuan bian : duo ceng bo mo ji yi gou jie / Cai Youman. / Abstract / 論文摘要 / Acknowledgements / Table of Contents / List of Figures / List of Tables / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Perovskite-type structure / Chapter 1.2 --- Metal-insulator transition / Chapter 1.3 --- Magnetoresistance / Chapter 1.3.1 --- Giant magnetoresistance (GMR) / Chapter 1.3.2.1 --- Colossal magnetoresistance (CMR) in perovskite manganites / Chapter 1.3.2.2 --- Possible origin of CMR / Chapter 1.4 --- Brief review of p-n junction between perovskite manganites and STON (001) / Chapter 1.5 --- Our project / Chapter 1.6 --- Scope of this thesis work / References / Chapter Chapter 2 --- Preparation and characterization of manganite thin films / Chapter 2.1 --- Thin film deposition / Chapter 2.1.1 --- Facing-target sputtering (FTS) / Chapter 2.1.2 --- Vacuum system / Chapter 2.1.3 --- Deposition procedure / Chapter 2.1.4 --- Deposition conditions / Chapter 2.1.5 --- Oxygen annealing system / Chapter 2.1.6 --- Silver electrode coating system / Chapter 2.2 --- Characterization / Chapter 2.2.1 --- Alpha step profilometer / Chapter 2.2.2 --- X-ray diffraction (XRD) / Chapter 2.2.3 --- Transport property measurement / References / Chapter Chapter 3 --- [LCSMO/PCMO] multilayers / Chapter 3.1 --- [LCSMO (100 A)/PCMO (X A)] multilayers / Chapter 3.1.1 --- Sample preparation / Chapter 3.1.2 --- Results and discussion / Chapter 3.1.2.1 --- Structural analysis / Chapter 3.1.2.2 --- Transport properties / Chapter 3.2 --- [LCSMO (50 A)/PCMO (X A)] multilayers / Chapter 3.2.1 --- Sample preparation / Chapter 3.2.2 --- Results and discussion / Chapter 3.2.2.1 --- Structural analysis / Chapter 3.2.2.2 --- Transport properties / References / Chapter Chapter 4 --- [LSMO/PCMO] multilayers and LSMO/STON p-n junction / Chapter 4.1 --- [LSMO/PCMO] multilayers / Chapter 4.1.1 --- Sample preparation / Chapter 4.1.2 --- Results and discussion / Chapter 4.1.2.1 --- Structural analysis / Chapter 4.1.2.2 --- Magnetization / Chapter 4.2 --- LSMO/STON heterojunction / Chapter 4.2.1 --- Sample preparation / Chapter 4.2.2 --- Results and discussion / Chapter 4.2.2.1 --- Structural analysis / Chapter 4.2.2.2 --- Metal insulator transition of LSMO revealed by four point I-V measurement / Chapter 4.3 --- Conclusion / References / Chapter 5 Conclusion / Chapter 5.1 --- Conclusion / Chapter 5.2 --- Future outlook

Ce travail de recherche porte sur l'étude d'un nouveau matériau issu de la combinaison de deux oxydes perovskites ferroélectriques Sr2Ta2O7 et La2Ti2O7 ; la solution solide résultante est formulée selon (Sr2Ta2O7)100 x(La2Ti2O7)x (STLTO). Notre étude comprend la synthèse de poudres, la réalisation de céramiques, le dépôt de films minces et leur caractérisation structurale, morphologique, élémentaire, optique, diélectrique et ferroélectrique. L'objectif visé à moyen terme pour ce matériau est son intégration dans des dispositifs hyperfréquences miniatures et reconfigurables. Pour cela, sont recherchées des permittivités élevées, variables sous champ électrique, afin d'atteindre une accordabilité du matériau, puis une reconfigurabilité en fréquence des antennes, par exemple. L'analyse structurale par diffraction des rayons X a confirmé, par la variation linéaire des paramètres de maille, la formation de la solution solide pour les compositions x ∊ [0-5]. Les analyses diélectriques menées à basses fréquences (1 100 kHz) sur les céramiques STLTO ont montré des valeurs maximales de permittivité (375) et d'accordabilité (55 % à 3 kV/mm), associées à des tangentes de pertes faibles (0,01), pour la composition x = 1,65. Les mesures en hautes fréquences (200 MHz – 18 GHz) sont en accord avec les résultats obtenus en basses fréquences. Le dépôt de films minces par pulvérisation cathodique réactive, réalisé à partir d'une cible de composition x = 1,65, produit des films s'apparentant à la phase Sr2,83Ta5O15, ce qui dénote une perte en strontium. Cependant, à basses fréquences, les films présentent des permittivités relativement élevées (130) pour des pertes faibles (0,01) avec une accordabilité modérée (A = 14,5% à 340 kV/cm à f =100 kHz). Le dépôt de films minces oxynitrures (Sr,La)(Ta,Ti)O2N, réalisé en atmosphère réactive Ar + N2, mènent à des échantillons colorés ayant des permittivités élevées (jusqu'à 3000 environ), mais avec des pertes également élevées (jusqu'à 2) et sans accordabilité. Par ailleurs, l'étude de films SrTaO2N a montré que ces composés sont adaptés pour la décomposition de l'eau sous lumière visible. / This research focuses on the study of a new material resulting from the combination of two ferroelectric perovskite oxides Sr2Ta2O7 and La2Ti2O7; the resulting solid solution is formulating according to (Sr2Ta2O7)100 x(La2Ti2O7)x (STLTO). Our study includes the synthesis of powders, the realization of ceramics, thin film deposition and their structural, morphological, elemental, optical, dielectric and ferroelectric characterizations. The medium-term objective for this material is its integration into miniature and reconfigurable microwave devices. For this, high permittivity, variable under electric field, is required in order to achieve a tunability of the material, then a reconfigurability of the antennas, for example. Structural analysis by X-ray diffraction confirmed, by the linear variation of the cell parameters, the formation of the solid solution for the compositions x ∊ [0-5]. The dielectric analyzes carried out at low frequencies (1 - 100 kHz) on STLTO ceramics showed maximum values of permittivity (375) and tunability (55% at 3 kV/cm), associated with weak loss tangents (0,01), for the composition x = 1.65. The measurements at high frequencies (200 MHz – 18 GHz) are in agreement with the results obtained at low frequencies. The deposition of thin film by reactive sputtering, made from a target of composition x = 1.65, produces films similar at Sr2.83Ta5O15 phase, which denotes a loss of strontium. However, at low frequencies, the films have relatively high permittivity (130) for low losses (0.01) with moderate tunability (A= 14.5% at 340 kV/cm at f = 100 kHz). Deposition of oxynitride thin film (Sr,La)(Ta,Ti)O2N, carried out in Ar + N2 reactive atmosphere, leads to coloured samples having high permittivity (up to about 3000), but with equally high losses (up to 2) and without tunability. Moreover, the study of SrTaO2N showed that these compounds are suitable for the decomposition of water under visible light.

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Materials chemistry is essentially concerned with the design/synthesis of new solids endowed with functional properties that could be of relevance to today’s materials technology. Among the large variety of solid materials that attract attention, metal oxides continue to contribute significantly to current materials chemistry. A wide variety of oxide materials (based on rocksalt, spinel, corundum, perovskite, garnet, pyrochlore and other structures) and their properties have been investigated over the years. Most of these oxides are derived from the transition metals. Transition metal oxides with structures derived from metal-oxygen (MO6) octahedra, in particular, display an array of exotic properties with potential or proven technological application. While it is traditionally believed that the partially filled d shell (dn : 0 < n < 10) of the transition metal atoms plays a crucial role in deciding the electronic properties, the significance of d0 metal atoms for the properties (and structure) of transition metal oxides is not fully recognized. Magnetism (SrRuO3, Fe3O4), metallicity (ReO3, LaNiO3), colossal magnetoresistance (La1-xCaxMnO3) and superconductivity (La2xSrxCuO4, Sr2RuO4) are some of the properties that can be traced to the presence of partially filled d shell, while properties like ferroelectricity (BaTiO3), piezoelectricity (PbZr1-xTixO3) and nonlinear optical response (LiNbO3) could be traced to the presence of transition metals (TiIV, ZrIV, NbV) with d0 electronic configuration. The empty d orbitals on the metal atoms constitute the low lying unoccupied states (LUMO) that mix with the highest occupied states (HOMO) of the ligand atoms (oxygen) through special chemical bonding effects (second order Jahn-Teller effect, SOJT). This mixing results, among others, in out-of-centre distortion(s) of the MO6 octahedra and this distortion is at the heart of several properties mentioned above. Among the transition metal oxide structures based on MO6 octahedra, three structures are noteworthy: the perovskite, the pyrochlore and the rutile. The AMO3 perovskite structure consists of a three-dimensional framework of corner sharing MO6 octahedra in which the A cation occupies the dodecahedral site surrounded by twelve oxide ions. The perovskite structure can accommodate a large variety of substitutions at both the A and the M sites as well as vacancies at the A/O sites, giving a large number of derivatives. Several variants of the perovskite structure are also known, for instance, the layered perovskites and ordered perovskites. Many nonperovskite structures are also known for the composition AMO3 : hexagonal YMnO3 is an alternative structure for AMO3 composition where manganese exists as MnO5 trigonal bipyramids. The A2M2O7 pyrochlore structure is also based on a corner-connected network of MO6 octahedra which interpenetrates an A2O network. The rutile (TiO2) is a well-known structure consisting of chains of edge-sharing MO6 octahedra, which are connected through corners to adjacent chains. A large number of oxide materials based on the above three structure types have been reported : for example, perovskite [Ba3ZnTa2O9 (microwave telecommunication ceramic), Pb3MgNb2O9 (relaxor ferroelectric), Bi4Ti3O12 (high temperature ferroelectric)], pyrochlore [Nd2Mo2O7 (metallic ferromagnet), AOs2O6 for A = K, Rb, Cs (superconductor)] and rutile [TiO2 (photocatalyst), CrO2 (metallic ferromagnet), VO2 (insulator-metal transition)]. Considering the current interest in oxide materials of these three structure types which continue to generate new variants and novel properties, we undertook the present research project to synthesize new derivatives of these structure types, and characterize their structures and relevant electronic properties. In doing so, we recognized that synthesis based on an understanding of the reactivity of the constituents and crystal chemistry of the expected products plays a crucial role in this effort. Accordingly, we tailored several new compositions of AMO3, A2M2O7 and MO2 stoichiometries and adopted appropriate methodologies for their synthesis. We have characterized the structures and properties of the solid products by means of state-of-the-art methods available to us. There are two main approaches to the synthesis of nonmolecular inorganic solids: conventional ceramic route and chimie douce / soft chemistry routes. In the ceramic route, solid reactants are heated at elevated temperatures for long durations with intermittent mixing/grinding until the reaction is complete. Chimie douce routes, on the other hand, utilize gentle reactions such as dehydration, decomposition, intercalation, ion exchange, and so on to synthesize the desired phases. The ceramic route generally provides access to the thermodynamically controlled product(s), while chimie douce routes allow access to metastable phases (kinetically controlled product(s)). Disadvantages notwithstanding, the ceramic route has been the mainstay of materials chemistry and several important materials continue to be discovered / synthesized by this route. The choice of the synthetic route based on an understanding of the crystal chemical preferences and the reactivities of the constituents involved is often crucial to achieve the desired final products. The present thesis is devoted to the synthesis and investigation of MO6 octahedra-based oxides belonging to the perovskite, pyrochlore and rutile structure types wherein we have explored alternate synthetic strategies (perovskite-based Ba3MM'2O9 telecommunication ceramics and a solution route for the synthesis of ruthenium-based pyrochlores) and probed structure-property relations of perovskite oxides (Ba3MM'M''O9 oxides for various M/M'/M'' atoms) as well as formation of new derivatives of layered Aurivillius phases. In addition, we have also synthesized new noncentrosymmetric oxides possessing the YMnO3 structure. Our investigation of rutile based oxides has resulted in the discovery of a new lead-free relaxor ferroelectric material, FeTiTaO6. Given that the lone pair PbII:6s2 plays a crucial role in the ferroelectric properties of Pb-based perovskite oxides, we have also investigated members of the Pb1-xLix/2Lax/2TiO3 system for their structure and dielectric response. The present thesis describes the results of these investigations in eight chapters. Chapter 1 provides a general introduction to oxides of the perovskite, pyrochlore and rutile structures. In Chapter 2, we describe a new one-pot metathesis strategy for the synthesis of dielectric ceramics Ba3MM'2O9 (M = Mg, Ni, Zn; M' = Nb, Ta). Rietveld refinement of X-ray diffraction data shows near-complete ordering of M-site ions in many cases. The dielectric properties of the products synthesized are found to be in reasonable agreement with reported data. The synthesis of ordered materials at lower temperatures (~1100 °C) than that employed in the conventional ceramic route (~1500 °C) is a significant result of this work. Chapter 3 presents a study of Ba3MIIMIVWO9 (MII = Ca, Zn; MIV = Ti, Zr) perovskite oxides for the purpose of synthesizing new dielectric ceramic materials and to gain understanding of the factors that stabilize 3C vs. 6H structures. In general, a 1:2-ordered 6H perovskite structure is stabilized at high temperatures (1300 °C) for all of the Ba3MIITiWO9 oxides investigated. An intermediate phase possessing a partially ordered 1:1 double perovskite (3C) structure with the cation distribution, Ba2(Zn2/3Ti1/3)(W2/3Ti1/3)O6, is obtained at 1200 °C for Ba3ZnTiWO9. A metastable perovskite, Ba3CaZrWO9, that adopts the 1:1 3C structure has also been synthesized by a low-temperature metathesis route. Besides yielding several new perovskite oxides that may be useful as dielectric ceramics, the investigation provides new insights into the complex interplay of crystal chemistry (tolerance factor) and chemical bonding (anion polarization and d0-induced distortion of metaloxygen octahedra) in the stabilization of 6H versus 3C perovskite structures for the Ba3MIIMIVWO9 series. In Chapter 4, we describe the synthesis and investigation of the structure and dielectric properties of Ba3MIIITiMVO9 (MIII = Fe, Ga, Y, Lu; MV = Nb, Ta, Sb) perovskite oxides. The MV = Nb, Ta oxides adopt disordered/partially ordered 3C perovskite structures, where all the MIII/Ti/MV metal-oxygen octahedra are corner-connected. In contrast, the MV = Sb oxides show a distinct preference for the 6H structure, where SbV/TiIV metal-oxygen octahedra share a common face, forming (Sb,Ti)O9 dimers, that are corner-connected to the MIIIO6 octahedra. Investigation of dielectric properties of MIII = Y/Lu, MV = Nb/Ta oxides reveals a normal low loss dielectric behaviour with ε = 30 – 50 in the temperature range 50 – 350 °C. The MIII = Fe, MV = Nb/Ta members show a dielectric behaviour similar to relaxor ferroelectric materials. Chapter 5 deals with a study of isomorphous substitution of several metal atoms in two Aurivillius structures, Bi5TiNbWO15 and Bi4Ti3O12, in an effort to probe structure-property correlations. These investigations have led to the synthesis of new derivatives, Bi4LnTiMWO15 (Ln, = La, Pr; M = Nb, Ta), as well as Bi4PbNb2WO15 and Bi3LaPbNb2WO15, that largely retain the Aurivillius intergrowth structure of the parent oxide Bi5TiNbWO15, but characteristically tend toward a centrosymmetric / tetragonal structure for the Ln-substituted derivatives. On the other hand, coupled substitution, 2TiIV Æ MV + FeIII in Bi4Ti3O12, yields new Aurivillius phases, Bi4Ti3-2xNbxFexO12 (x = 0.25, 0.50) and Bi4Ti3-2xTaxFexO12 (x = 0.25) that retain the orthorhombic noncentrosymmetric structure of the parent Bi4Ti3O12. Chapter 6 describes the design and synthesis of a new series of noncentrosymmetric oxides, R3Mn1.5CuV0.5O9 (R = Y, Ho, Er, Tm, Yb, Lu) possessing the YMnO3 structure. Investigation of the Lu-Mn-Cu-V-O system revealed the existence of an isostructural solid solution series, Lu3Mn3-3xCu2xVxO9 for 0 < x ≤ 0.75. Magnetic and dielectric properties of the oxides are consistent with a random distribution of Mn3+, Cu2+ and V5+ atoms that preserves the noncentrosymmetric RMnO3 structure. An exploratory investigation of the synthesis, structure and electronic properties of new ruthenium(IV) pyrochlore oxides and their manganese-substituted derivatives is presented in Chapter 7. The richness of the electronic properties of ruthenium-based metal oxides is affirmed by the results which revealed several novel electronic ground states : a metallic and Pauli paramagnetic state for BiPbRu2O6.5 that turns into a semiconducting ferromagnetic spin-glass state at 50 K for BiPbRuMnO6.5 ; a metallic state that likely shows a charge density wave (CDW) instability at 50-225 K for Bi1.50Zn0.50Ru2O6.75, that is suppressed by manganese substitution in Bi1.50Zn0.50Ru1.75Mn0.25O6.50, and a metallic ferromagnetic spin-glass-like state for Pb2Ru1.75Mn0.25O6.15. We describe the investigation of the structure and dielectric properties of rutile-based MTiTaO6 (M = Al, Cr, Fe) in Chapter 8. All the oxides possess disordered rutile structure. FeTiTaO6 shows a strong relaxor ferroelectric effect, while CrTiTaO6 shows a weaker relaxor ferroelectric behaviour. This work is significant for two reasons: the new material is lead-free and it is based on the rutile structure, unlike the conventional relaxors which are mostly derived from the perovskite structure. The work presented in the thesis is carried out by the candidate as a part of the Ph.D. training programme and most of it has been published in the literature. She hopes that the studies reported here will constitute a worthwhile contribution to materials chemistry in general.

Oxides of ABO3 composition (A = alkali, alkaline earth or rare earth metal in general, B = transition metal) constitute a large family of metal oxides of current interest to solid state and materials chemistry. Among the several structure types exhibited by ABO3 oxides (ilmenite, LiNbO3, perovskite, YAIO3/YMnO3, KSbO3, pyrochlore, among others), the perovskite structure is probably the most well known and widely investigated. The ideal perovskite structure consists of a three-dimensional (3D) framework of corner-sharing BO6 octahedra in which the A cation resides in the dodecahedral site surrounded by twelve oxide ions. The ideal cubic structure occurs when the Gold Schmidt’s tolerance factor, t = (rA + ro)/{V2 (rB + ro)}, adopts a value of unity and the A-O and B-O bond distances are perfectly matched. The flexibility of the perovskite structure towards a wide variety of substitutions at both A and B sites gives rise to a very large number (several hundreds) of perovskite derivatives with subtle variations in structure. The perovskite structure can also tolerate vacancies at both the A and O sites giving ordered superstructures. Members of y4BO3 oxides have numerous properties that find technological application, such as nonlinear optical response (LiNbO3), Ferro electricity (BaTiO3), piezoelectricity (PbZn_xTixO3), magneto ferroelectricity (YMnO3), superconductivity (Bai_xKxBi03)5 colossal magnetoresistance (La^xCaxMnO3) and ionic conductivity [(Lil_a)TiO3] Ordering of cations at the A and B sites of the perovskite structure is an important phenomenon. Ordering of B site cations in double (/42BB'O6) and multiple (/43BB'2Og) perovskites gives rise to newer and interesting materials properties For example, 1*1 ordered Sr2FeMoO6 and Sr2FeReO6 are half-metallic ferrimagnets; Pb3MgNb2O9 is a relaxor ferroelectric; Ba3ZnTa2O9 is a low loss dielectric used in telecommunication and, last but not least, Ba3CoNb2O9 is a visible light driven photocatalyst. Realization of these properties in these materials depends crucially on the ordering/or otherwise of the B site cat ions in the perovskite structure. Furthermore, ordering of not only the metal atoms but also the oxygen/oxygen vacancies in the perovskite structure is equally important for the occurrence of superconductivity in the cuprate superconductor, YBa2Cu3O7. The ideal perovskite structure gives way to hexagonal YMnO3/YAIO3 structure for smaller A cations (tolerance factor, t < 1). Oxides of this structure are attracting current attention for the realization of multiple magnetoferroic properties. On the other hand, for larger A cations (tolerance factor, t > 1), various perovskite polytypic structures are formed. For example, BaNiO3 forms a 2H polytypic structure, SrMnO3 and BaRuO3 adopts a 4H and 9R structures respectively, where the SO6 octahedra share faces or faces and corners. Besides the foregoing 3D perovskites, a number of layered variants of the perovskite structure are also known. The most common layered perovskites are the Aurivillius phases, (Bi2O2)[A»-iBnO3n+iL the Ruddlesden-Popper phases, /4'2|7ln_iBnO3n+1], and the Dion-Jacobson phases, A[An^BnOzn+-\]' The two-dimensional (2D) perovskite unit, [^n-iBnOsn+i], which could be visualized as formed by slicing the 3D perovskite structure along <001>p is common for all the three layered perovskite series. The perovskite slabs are stacked alternately with various charge-balancing units, for example, with [Bi2O2]2+ in the Aurivillius phases and two alkali/alkaline earth cations (A+JA2+) in the Ruddlesden-Popper phases etc. Members of the layered perovskites are also important from the point of view of materials properties. For example, 2D magnetism (K2NiF4), superconductivity (La2-xSrxCuO4), ion exchange, Bronsted acidity, intercalation, exfoliation (K2La2Ti3Oio and CsCa2Nb3O10), photo catalysis (Rb2La2Ti30io) are some of the important materials properties found in layered perovskites. The high Tc-superconductors, Bi2Sr2CaCu2O8+XJ TI2Ba2Ca2Cu3Oi0, TIBa2Ca2Cu3O9 and HgBa2Ca2Cu3O8+x, also belong to the family of layered perovskites where the defective perovskite cuprate sheets are interleaved by other 2D entities like (Bi2O2), (TI2O2), (TIO) or (HgOx). In addition, Aurivillius phases, such as Bi2SrTa209 and Bi325Lao75Ti3Oi2, in thin film geometry are candidate materials for non-volatile ferroelectric memory devices. Synthesis plays a key role in realizing new structures and materials properties for ABO3 oxides. The conventional synthetic methods (ceramic method) involve mixing and heating of solid reactants at elevated temperatures. Although this approach continues to be employed to synthesize new materials, it is often limited by the fact that it yields thermodynamically stable phases. Since many of the perovskite oxides showing useful materials properties are metastable in nature and are required in the form of fine particles (free-standing / monodisperse / submicron or nanometer dimensions) for application, the ceramic methods are of no avail for this purpose. Therefore, materials chemists constantly endeavor to develop alternate synthetic routes that enable them to synthesize novel oxides under mild conditions. Typical examples of metastable perovskites are: the super conducting cuprates (e.g. TlosPbosS^CaC^Og) and perovskite based lithium ion conductors (La2/3-xLi3XDi/3-2xTiO3). Also the control of oxidation states in double perovskites, such as Sr2FeMoO6 and Sr2FeRe06 and pyrochlores such as Pb2MnReC>6, cannot be achieved by conventional means. Therefore, the synthesis of such metastable phases requires special synthetic strategies that involve soft chemistry (chimie douce) methods where mild reactions/reaction conditions are employed to access metastable phases. The present thesis is mainly devoted to an investigation of perovskite related oxides towards developing new synthetic strategies and materials as well as exploring hydrogen insertion - a novel materials property - in certain members of this family. Solid-state metathesis (SSM) reactions provide a convenient route for the synthesis of a wide variety of non-oxide ceramic materials such as, bondes, carbides, silicides, pnictides and chalcogenides. A typical metathesis reaction, for example, M0CI5 + 5/2 Na2S -» MoS2 + 5 NaCI + 1/2 S (1) involves exchange of atoms/ions between the reactants and is accompanied by a large enthalpy change (AHm = - 890 kJ mol"1) and high adiabatic reaction temperature (Tm = 1413 °C). The reactions are often self-propagating and believed to be driven by the formation of stable salt byproducts such as alkali halides with high lattice energy. In our laboratory we have developed a different kind of metathesis reaction for the synthesis of perovskite related oxides, a typical example being, K2La2Ti30io + 2 BiOCI -* [Bi2O2]La2Ti3O10 + 2 KCI. A major difference between metathesis reactions (1) and (2) is that unlike (1), reaction (2) is not self-propagating, requiring longer duration. In this study, we have investigated metathesis reactions of the second kind at some length for the synthesis of perovskite related oxides. We found that rocksalt oxides such as UMO2 (M = Mn, Co) and Li2TiO3 constitute convenient precursors for the formation of v4BO3 perovskite oxides in metathesis reactions with appropriate reaction partners such as halides, oxyhalides or sulphates, LiCoO2 + LaOCl -» LaCoO3 + LiCt (3) LiMnO2 + LaOCl + x/2 O2 -> LaMnO3+x + LiCI (4) Li2TiO3 + PbSO4 -» PbTiO3 + Li2SO4. (5) We could synthesize not only well known ABO3 oxides but also functional perovskites such as PbZr0 4sTio 52O3 (PZT), La2/3Cai/3MnO3 as well as superconducting BaPbo75Bio2s03 by this method. We could also synthesize La2CuO4 and its superconducting analogues, La185^oi5Cu04 (A = Sr, Ba), by the same method using Li2CuO2 and LaOCl. For the synthesis of double perovskites A2BB%OQ by this method however, appropriate lithium containing rocksalt precursor oxides are not known in the literature. Therefore, we first synthesized rocksalt precursor oxides of the general formula Li4MWO6 (M = Mg, Mn, Fe, Ni) and established their identity. Using these precursor oxides, we could synthesize the double perovskite oxides Sr2MWO6 (M = Mg, Mn, Fe, Ni) in the metathesis reaction Li4MWO6 + 2 SrCI2 -» Sr2MWO6 + 4 LiC Significantly, the double perovskites are formed with an ordered structure at relatively low temperatures (750 - 800 °C) as compared to the high temperatures (up to 1400 °C) usually employed for the synthesis of these materials by conventional ceramic approach. Next, we investigated ABO$ compositions corresponding to the formula for 6 = Cu and Ni, where we could obtain a YAIO3 superstructure consisting of triangular Cu clusters for 6 = Cu, whereas a perovskite phase for B = Ni. Moreover, the Cu-phase appears to be a unique line phase formed around LasCi^VOg composition, whereas a continuous series of GdFeO3-like perovskite oxides are formed for LaNii»xVxO3 (0 < x < 1/3)forS = Ni. Considering the current interest in bringing different transition metal ions (d°/dn electronic configuration) in the same perovskite related structure towards developing multiferroic materials, we investigated the substitution of aliovalent cations in a typical Aurivillius phase, Bi2Sr2Nb2TiOi2. We have characterized new aliovalent cation substituted Aurivillius phases, Bi2SrNaNb2TaOi2, Bi2Sr2Nb2Zr012J Bi2Sr2Nb2 5Feo50i2 and Bi2Sr2Nb2 ezZno 33O12. Lastly, we investigated the interaction of hydrogen with perovskite oxides, /\MnO3 (A = Ca, Sr, Ba) in an attempt to characterize possible existence of hydrogen-inserted oxide materials. An oxide-hydride of the formula LaSrCoO3H07 has recently been reported in the literature. Conventionally, the interaction of hydrogen with perovskite related oxides is known to result in either anion deficient phases (e.g. CaMnO3 -> Ca2Mn205), or hydrogen inserted materials, 'hydrogen bronzes', (e. g. HXWO3, HxBaRuO3), where hydrogen acts as an electron donor (H -^ H+ + e). We have characterized a new mode of hydrogen incorporation in Pt dispersed BaMnO3 and SrMnO3. Detailed investigation of the hydrogen sorption behaviour of 1 atom % Pt dispersed materials showed that about 1.25 mass % of hydrogen is inserted per mole of BaMnO3/Pt, corresponding to an insertion of - 3 hydrogen atoms giving 'BaMnOsHs'. While the exact nature of inserted hydrogen is yet to be established unambiguously, our results suggest that the inserted hydrogen is unlikely to be protonic (H+) in the hydrogen insertion product, BaMnO3H3. The results of these investigations are presented in the thesis consisting of seven chapters. Chapter 1 gives an overview of perovskite related oxides - structure, properties and synthesis. Chapter 2 presents metathesis as a general route for the synthesis of ABO3 oxides and illustrates the method by transforming several rocksalt oxides such as LiCoO2, Li2Mn03 and Li2Ti03 to corresponding ABO3 oxides, LaCoO3, /\MnO3 and ATiO3 (A = Ca, Sr, Ba). Uniformly in all the cases, the perovskite oxides are obtained in the form of loosely connected submicron sized particles at considerably lower temperatures than those usually employed for their synthesis by ceramic methods. Thermodynamic calculations have also been carried out to probe into the driving force of metathesis reactions involved in the synthesis. Chapter 3 describes an extension of the metathesis route for the synthesis of double perovskites, Sr2MWO6 (M = Mg, Mn, Fe, Ni). For this purpose, first we synthesized new rocksalt oxides of the general formula, Li4MWO6 (M = Mg, Mn, Fe, Ni). The oxides adopt rocksalt superstructures related to Li4MgReO6 (for M = Mg, Mn, Ni) and U4WO5 (for M = Fe). Metathesis reaction between Li4MWO6 and SrCi2 at 750 - 800 °C yields the corresponding double perovskites where the octahedral site M and W are ordered in the long range. Formation of ordered perovskite oxides at relatively low temperatures (750 - 800 °C) by the metathesis route is a significant result, considering that synthesis of these oxides by conventional ceramic method requires much higher temperatures (1300 - 1400 °C) and prolonged annealing. Synthesis of La2CuO4, Nd2CuO4 and super conducting La-j 85>4oi5Cu04 (A = Sr, Ba) by the metathesis route is described in Chapter 4. Chapter 5 deals with synthesis, structure and magnetic properties of mixed-metal oxides of ABO3 composition in the La-6-V-O (6 = Ni, Cu) systems. While the B = Ni oxides adopt GdFeO3-like perovskite structure containing disordered nickel and vanadium at the octahedral B site, La3Cu2VO9 crystallizes in a YAIO3-type structure. A detailed investigation of the superstructure of nominal La3Cu2VO9 by WDS analysis and Rietveld refinement of powder XRD data reveals that the likely composition of the phase is Lai3Cu9V4O38 5, where the Cu and V atoms are ordered in a Vi3ah (ah = hexagonal a parameter of YAlCMike subcell) superstructure. Magnetic susceptibility data support the proposed superstructure consisting of triangular Cu3 clusters. The present work reveals the contrasting behaviour of La-Cu-V-O and La-Ni-V-0 systems, while a unique line-phase related to YAIO3 structure is formed around La3Cu2VO9 composition in the copper system, a continuous series of perovskite-GdFeO3 solid solutions, LaNi1.0CVxO3 for 0 < x < 1/3 seems to obtain in the nickel system. The chapter also describes the formation of a new transparent Cu(l) oxide, Lai4V6CuO365, and its characterization. This oxide was obtained during attempts to grow single crystals of LasC^VOg. Single crystal structure determination of Lai4V6CuO36 5 showed that the structure contains isolated VO43" tetrahedra and [OCuO]3" sticks dispersed in a lanthanum oxide network. Films of Lai4V6CuO36 5 were grown on R-plane sapphire by using pulsed laser deposition. Rutherford backscattering spectroscopic and X-ray diffraction analyses of the films showed oriented growth of the title phase, with an optical band gap of -~ 5 eV and n-type conductivity Chapter 6 presents the work on the flexibility of the Aurivillius structures for substitution of aliovalent/isovalent cations at both A and 6 sites of the perovskite slabs. For example, in a typical n = 3 member, Bi2Sr2Nb2TiOi2, substitution of both Sr and Na at the A site and Ta at the B site has enabled us to synthesize a new n = 3 member, Bi2SrNaNb2Ta0i2, where we see a preference of Nb for the terminal octahedral sheets. Similarly, aliovalent substitution only at the B site of the perovskite slabs of Bi2Sr2Nb2TiOi2 has yielded new members for specific compositions, Bi2Sr2Nb2ZrOi2, Bi2Sr2Nb2 5Feo50i2 and Bi2Sr2Nb2 67Zno33012 that tend to be oxygen-stoichiometric. The latter phases again show a preference of Nb for the terminal octahedral sites that are strongly distorted as compared to the middle octahedral site. This chapter also describes substitution of La3+ for Bi3+ in the perovskite slabs of Bi4Nb30i5 stabilizing a new series of n = 1/ n = 2 intergrowth Aurivillius phases of the formulas, Bi4LnNb3Oi5 (Ln = La, Pr, Nd) and Bi4LaTa30i5. The present work suggests that replacement of Bi3+: 6s2 lone pair ion by non-6s2 cations such as Sr2"* and La3+ in the perovskite slabs of Aurivillius phases tends to render the structure Centro symmetric and the materials lose NLOSHG response. Chapter 7 describes our investigation of the interaction of hydrogen with alkaline earth manganites (IV) >AMnO3 (>A = Ca, Sr, Ba) dispersed with 1 atom % Pt. The result shows an unprecedented uptake of hydrogen by BaMnO3/Pt to the extent of - 1.25 mass % at moderate temperatures (190 - 260 °C) and ambient pressure. Gravimetric sorption isotherms and mass spectrometric analysis of the desorption products indicate that approximately three hydrogen atoms per mole of BaMnCVPt is inserted reversibly. The nature of hydrogen in the insertion product, BaMnO3H3, is discussed in the light of the structure of BaMnC>3. The work presented in the thesis is carried out by the candidate as a part of the Ph. D. training programme and most of it has been published in the literature. He hopes that the studies reported here will constitute a worthwhile contribution to the materials chemistry of ABO3 oxides in general.