Over the past decades, microwave sintering has been investigated, and the effects of microwave sintering have been demonstrated, however there is still uncertainty as to what is causing the enhancements known as the microwave effect . For a better understanding of the microwave effect , the effect of microwaves on the pore size distribution during densification has been investigated for submicron-sized zinc oxide (ZnO), which was sintered with conventional heating and varying amounts of microwave power but always maintaining exactly the same time-temperature profile. Initially, the density of the sintered samples was measured and compared; this proved that the densification of the hybrid sintered samples was increased and that the higher the level of microwaves used, the more it enhanced the densification. After this, the porosity was investigated through the use of nitrogen adsorption analysis, mercury porosimetry and Field Emission Gun Scanning Electron Microscopy (FEGSEM). Initially, it was found that sintering with microwaves reduces pores faster than for conventional sintering as expected. However, the experiments also revealed that the mechanisms of the reduction in the porosity were not different for microwave sintering compared to conventional sintering. When the porosity was compared at equivalent densities, it was observed that there was no significant difference, either in terms of the amount of porosity or the microstructure development. Since the structural development was the same for both conventional and hybrid sintering, it was concluded that the cause for the enhancement of the densification was enhanced diffusion caused by an additional driving force induced by the microwave field. The investigation of the solid-state reaction between zinc oxide and alumina was designed to investigate whether the diffusion associated with reactions was also enhanced by the use of microwaves. Therefore, zinc oxide and alumina samples were reacted as diffusion couples using conventional and hybrid heating, the latter with varying amounts of microwave power. The analyses of the reaction layer using FEGSEM showed an increase in the reaction product layer thickness when hybrid heating was used, with a higher level of microwaves yielding more growth. These results supported the view that the enhanced reaction rates were caused by enhanced diffusion, again caused by an additional driving force induced by the microwave field. For both the densification and reaction cases, the most likely additional driving force is considered to be the ponderomotive effect.

Indiana University-Purdue University Indianapolis (IUPUI) / Three parts consist of my thesis work centered on the synthesis of inorganic phosphates and then metal organic frame work (MOF). The first part is the synthesis of mesoporous chromium phosphates using the room temperature solid state reaction (SSR)approach. One of the major aims of this work is to fill the gap of lacking a low cost, low or zero pollution, easy method to synthesize phosphates. The room temperature solid state reaction has been demonstrated in this work is such a method. Mesoporous chromium phosphates were prepared using the solid state reaction at low temperature using CrCl3.6H2O, and NaH2PO4.2H2O as precursors and the surfactant cetyltrimethyl ammonium bromide (CTAB) as template. The synthesized chromium phosphates were characterized by XRD, EDS, HR-TEM, N2-physisorption, TG-DSC and UV-Vis spectroscopies. The results indicate that chromium phosphate mesophases were formed only at atomic ratios of P/Cr ≥ 1.8. The mesophase for P/Cr = 2.0 phosphate possessed the highest ordering of pore array, with a specific surface area as high as 250.78 m2/g and an average pore size of 3.48nm. The catalytic performance of the chromium phosphates was examined by employing a model reaction, namely the dehydration of isopropanol to propene. The results indicated that all synthesized chromium phosphates exhibited significantly higher isopropanol conversions and propene yields than that synthesized via the conventional precipitation route. The highest propene selectivity (96.43%) at the highest isopropanol conversion (93.10%) has been obtained over the mesoporous chromium phosphate catalyst synthesized with a P/Cr atomic ratio of 2.0. The formation mechanism of the mesoporous chromium phosphate was investigated by FTIR technique.The results show that CTAB template plays a key role in the formation of mesoporous chromium phosphates. Mesoporous lithium manganese phosphates were also successfully synthesized using the same approach of solid state reaction (SSR) at low temperature by using LiC2O3.6H2O, MnCl2.6H2O and NH4H2PO4.2H2O as precursors and the surfactant cetyltrimethyl ammonium bromide (CTAB) as template. The synthesized lithium manganese phosphates were characterized by XRD, EDS, SEM, HR-TEM, N2-physisorption. The results show that the synthesized meoporous lithium manganese phosphates exhibited a high specific surface area (256.63 m2/g) and a narrow pore size distribution. The electrochemical tests of Li-ion batteries were performed and the results show that the charge voltage could increase to be 3.60 V while the first time discharge capacity could be as high as 100 mAh/g. The Nitro-Cu-MOF complexes, a new class of metal organic frameworks, have been successfully synthesized using a conventional thermal reaction. The obtained Nitro-Cu-MOFs have a specific surface area of 576.27 m2/g and a pore volume of 0.32 m3/g.The gas uptake of the obtained Nitro-Cu-MOFs at 60 psi is 68 mg/g (sorbate/sorbent) at 298 K for carbon dioxide, which is much higher than that of the Cu-MOFs, 31 mg/g at 298 K for carbon dioxide.

A introdução de cálcio e lítio como aditivos de sinterização na céria: 10% mol gadolínia foi investigada com o intuito de verificar sua influência na densificação e condutividade elétrica das cerâmicas sinterizadas. Pós contendo de 0 a 1,5% mol do metal foram preparados tanto por reação em estado sólido quanto pela co-precipitação dos oxalatos. As principais técnicas de caracterização utilizadas foram análise térmica, difração de raios X, microscopia eletrônica de varredura e medida da condutividade elétrica por espectroscopia de impedância. Os resultados obtidos mostraram que cerâmicas densas podem ser obtidas utilizando ambos os aditivos. O aumento no teor do aditivo resulta em aumento na densificação. A forma de adição, por reação em estado sólido ou por coprecipitação exerce influência na condutividade elétrica. A adição de cálcio promove maior crescimento dos grãos que o lítio. A condutividade elétrica das amostras contendo o segundo aditivo é inferior à da céria-gadolínia pura. Ambos os aditivos exercem influência na condutividade intergranular. Adição de cálcio resulta também em diminuição da condutividade intragranular. Os aditivos favorecem a exudação do gadolínio. / In this work, the use of calcium and lithium as sintering aid to gadolinia-doped ceria was systematically investigated. The main purpose was to verify the influence of these additives on the densification and electrical conductivity of sintered ceramics. Powder compositions containing up to 1.5 mol% (metal basis) of calcium or lithium were prepared by both solid state reaction and oxalate coprecipitation methods. The main characterization techniques were thermal analyses, X-ray diffraction, scanning electron microscopy and electrical conductivity by impedance spectroscopy. Both additives promoted densification of gadolinia-doped ceria. The densification increases with increasing the additive content. Different effects on microstructure and electrical conductivity result from the method of preparation, e.g., solid state reaction or coprecipitation. Calcium addition greatly enhances the grain growth compared to lithium addition. The electrical conductivity of specimens containing a second additive is lower than that of pure gadolinia-doped ceria. Both additives influence the intergranular conductivity and favor the exudation of gadolinium out of the solid solution.

A introdução de cálcio e lítio como aditivos de sinterização na céria: 10% mol gadolínia foi investigada com o intuito de verificar sua influência na densificação e condutividade elétrica das cerâmicas sinterizadas. Pós contendo de 0 a 1,5% mol do metal foram preparados tanto por reação em estado sólido quanto pela co-precipitação dos oxalatos. As principais técnicas de caracterização utilizadas foram análise térmica, difração de raios X, microscopia eletrônica de varredura e medida da condutividade elétrica por espectroscopia de impedância. Os resultados obtidos mostraram que cerâmicas densas podem ser obtidas utilizando ambos os aditivos. O aumento no teor do aditivo resulta em aumento na densificação. A forma de adição, por reação em estado sólido ou por coprecipitação exerce influência na condutividade elétrica. A adição de cálcio promove maior crescimento dos grãos que o lítio. A condutividade elétrica das amostras contendo o segundo aditivo é inferior à da céria-gadolínia pura. Ambos os aditivos exercem influência na condutividade intergranular. Adição de cálcio resulta também em diminuição da condutividade intragranular. Os aditivos favorecem a exudação do gadolínio. / In this work, the use of calcium and lithium as sintering aid to gadolinia-doped ceria was systematically investigated. The main purpose was to verify the influence of these additives on the densification and electrical conductivity of sintered ceramics. Powder compositions containing up to 1.5 mol% (metal basis) of calcium or lithium were prepared by both solid state reaction and oxalate coprecipitation methods. The main characterization techniques were thermal analyses, X-ray diffraction, scanning electron microscopy and electrical conductivity by impedance spectroscopy. Both additives promoted densification of gadolinia-doped ceria. The densification increases with increasing the additive content. Different effects on microstructure and electrical conductivity result from the method of preparation, e.g., solid state reaction or coprecipitation. Calcium addition greatly enhances the grain growth compared to lithium addition. The electrical conductivity of specimens containing a second additive is lower than that of pure gadolinia-doped ceria. Both additives influence the intergranular conductivity and favor the exudation of gadolinium out of the solid solution.

FePt films with the L10 phase have potential applications for magnetic recording and permanent magnets due to its high magnetocrystalline anisotropy energy density. Heat treatment of n multilayer films is one approach to form the L10 FePt phase through a solid state reaction. This thesis has studied the diffusion and reaction of n multilayer films to form the L10 FePt phase and has used this understanding to construct exchange spring magnets. The process-structure-property relations of n multilayer films were systematically examined. The transmission electron microscopy (TEM) study of the annealed multilayers indicates that the Pt layer grows at the expense of Fe during annealing, forming a disordered fcc FePt phase by the interdiffusion of Fe into Pt. This thickening of the fcc Pt layer can be attributed to the higher solubilities of Fe into fcc Pt, as compared to the converse. For the range of film thickness studied, a continuous L10 FePt product layer that then thickens with further annealing is not found. Instead, the initial L10 FePt grains are distributed mainly on the grain boundaries within the fcc FePt layer and at the Fe/Pt interfaces and further transformation of the sample to the ordered L10 FePt phase proceeds coupled with the growth of the initial L10 FePt grains. A comprehensive study of annealed n films is provided concerning the phase fraction, grain size, nucleation/grain density, interdiffusivity, long-range order parameter, and texture, as well as magnetic properties. A method based on hollow cone dark field TEM is introduced to measure the volume fraction, grain size, and density of ordered L10 FePt phase grains in the annealed films, and low-angle X-ray diffraction is used to measure the effective Fe-Pt interdiffusivity. The process-structure-properties relations of two groups of samples with varying substrate temperature and periodicity are reported. The results demonstrate that the processing parameters (substrate temperature, periodicity) have a strong influence on the structure (effective interdiffusivity, L10 phase volume fraction, grain size, and density) and magnetic properties. The correlation of these parameters suggests that the annealed n multilayer films have limited nuclei, and the subsequent growth of L10 phase is very important to the extent of ordered phase formed. A correlation between the grain size of fcc FePt phase, grain size of the L10 FePt phase, the L10 FePt phase fraction, and magnetic properties strongly suggests that the phase transformation of fccL10 is highly dependent on the grain size of the parent fcc FePt phase. A selective phase growth model is proposed to explain the phenomena observed. An investigation of the influence of total film thickness on the phase formation of the L10 FePt phase in n multilayer films and a comparison of this to that of FePt co-deposited alloy films is also conducted. A general trend of greater L10 phase formation in thicker films was observed in both types of films. It was further found that the thickness dependence of the structure and of the magnetic properties in n multilayer films is much stronger than that in FePt alloy films. This is related to the greater chemical energy contained in n films than FePt alloy films, which is helpful for the L10 FePt phase growth. However, the initial nucleation temperature of n multilayers and co-deposited alloy films was found to be similar. An investigation of L10 FePt-based exchange spring magnets is presented based on our understanding of the L10 formation in n multilayer films. It is known that exchange coupling is an interfacial magnetic interaction and it was experimentally shown that this interaction is limited to within several nanometers of the interface. A higher degree of order of the hard phase is shown to increase the length scale slightly. Two approaches can be used to construct the magnets. For samples with composition close to stoichiometric L10 FePt, the achievement of higher energy product is limited by the average saturation magnetization, and therefore, a lower annealing temperature is beneficial to increase the energy product, allowing a larger fraction of disordered phase. For samples with higher Fe concentration, the (BH)max is limited by the low coercivity of annealed sample, and a higher annealing temperature is beneficial to increase the energy product.

In this work new novel cathode materials such as transition-metal sulfides, chlorides or fluorides were investigated and studied for their use in lithium ion thermal batteries. All cathodes were synthesized by a solid state reaction in sealed quartz tubes with a duration of firing for 1 week at high temperatures ( > 500 °C). All structures of compounds were probed by powder X-ray diffraction and the morphology and shape of crystallites of cathodes were characterized by scanning electron microscopy. The electrochemical properties of the batteries were investigated by galvanostatic discharge and galvanostatic intermittent titration technique at high temperatures (> 400 °C). All the batteries used as an anode Li₁₃Si₄, as an electrolyte LiCl-KCl eutectic and as separator MgO. All the products of the discharge mechanism were confirmed using powder X-ray diffraction and EDX analysis. CoNi₂S₄ and NiCo₂S₄ exhibit two voltage plateaux vs Li₁₃Si₄ at 500 °C, one at around 1.75 V and the second at 1.50 V. Capacities of 350 and 290 mA h g⁻¹ were achieved, respectively. NiS, Co₃S₄ and Co₉S₈ were confirmed as the products of discharge mechanism. ZrS₃ exhibits a single flat voltage plateau of 1.70 V at a current density of 11 mA/cm² and a capacity of 357 mA h g⁻¹, at 500 °C was obtained. A new material, LiZr₂S₄, was identified as the product of the electrochemical process, which can be indexed to a = 10.452(8) Å cubic unit cell. KNiCl₃ was tested at different current densities from 15 mA/cm² to 75 mA/cm² and a high cell voltage, with a capacity of 262 mA h g⁻¹ was achieved at 425 °C. Ni metal, KCl and LiCl were confirmed as the products of the discharge mechanism. Li₂MnCl₄ was tested at the same current densities as KNiCl₃ at 400 °C and a capacity of 254 mA h g⁻¹ was achieved. Mn metal and LiCl were confirmed as the products after discharge. Li₆VCl₈ has a capacity of 145 mA h g⁻¹ and a flat voltage plateau of 1.80 V at 500 °C. NiCl₂ has also a capacity of 360 mA h g⁻¹ and a high voltage profile of 2.25 V at 500 °C. CoCl₂ exhibits a lower capacity of 332 mA h g⁻¹ and lower voltage profile compared to NiCl₂ at 500 °C. CuF₂ and PbF₂ were tested at 500 °C. PbF₂ exhibits a single flat voltage plateau of 1.25 V and a capacity of 260 mA h g⁻¹ was obtained. CuF₂ has a high voltage profile but a voltage plateau could not be obtained.

Disertační práce se zabývá přípravou pokročilých keramických materiálů se zajímavými fyzikálními vlastnostmi. Materiály, připravené v rámci této práce, byly vyrobeny tuho-fázovými popř. hydrotermálními syntézami. První ze zkoumaných materiálů je elektrokeramika EuTiO3 s perovskitovou mřížkou. Absence termodynamických dat tohoto systému vedla k rozsáhlému experimentálnímu výzkumu vhodných podmínek jeho přípravy. Tři směsi práškových prekurzorů (Eu2O3 s Ti2O3 nebo TiO2 – rutil či anatas) byly homogenizovány mletím v planetovém mlýnu a formovány izostatickým tlakem 300 MPa. Vzniklé keramické polotovary diskového tvaru byly slinovány konvenčními metodami v redukčních atmosférách (Ar + 7 % H2 nebo pouze čistý H2) popř. pokročilou slinovací metodou Spark Plasma Sintering (SPS). Následně byl studován vliv slinovací metody, teploty, složení atmosféry a prodlevy na finální hustotu a fázovou čistotu vzorků. Tento výzkum vyústil v úspěšnou přípravu jednofázové EuTiO3 objemové keramiky s relativní hustotou vyšší než 95 % teoretické hustoty (%TH). S ohledem na dostupnou literaturu jsou tyto materiály jedinými publikovanými vzorky fázově čisté EuTiO3 keramiky s tak nízkou porozitou. Důležitost těchto výsledků je podložena čtyřmi publikacemi v impaktovaných časopisech, kde byly vlastnosti měřené na těchto vzorcích prezentovány. Spektra infračervené odrazivosti byla porovnána s výsledky v literatuře. Byla tak demonstrována nezbytnost fázově čistých vzorků s minimálním porozitou pro měření jejich reálných (neovlivněných) fyzikálních vlastností. Další výzkum byl zaměřen na hydrotermální syntézu (HTS) keramického prášku Eu0,5Na0,5TiO3. Prezentované HTS byly uskutečněny ve vysoce zásaditém prostředí vodných roztoků NaOH nebo KOH při teplotách 220 – 250 °C. Experimenty s různými koncentracemi prekurzorů (EuCl3 a TiCl4) a redukčních činidel vedly k přípravě jednofázového práškového perovskitu Eu0,5Na0,5TiO3 s krychlovými částicemi s rozměry pod 1 m. Jiný titaničitan - MgTiO3 – byl syntetizován tuho-fázovou reakcí směsi práškových prekurzorů MgO a TiO2. Směsi byly mechanicky aktivovány v kulovém mlýnu po dobu 0, 10, 40, 80 nebo 160 min. Keramická tělesa byla slinována pomocí dvou různých přístupů a to buď metodou Two-step Sintering (TSS) na teplotách 1300 °C (30 min) a následně 1200 °C (20 h) nebo nejprve konvenčním slinováním při 1300 °C popř. 1400 °C po dobu 30 min a poté ještě pomocí metody Hot Isostatic Press (HIP) na 1200 °C popř. 1280 °C. V případě HIP-ovaných vzorků při 1280 °C po 3 hodiny v inertní Ar atmosféře o tlaku 200 MPa byly získány fázově čisté keramické vzorky MgTiO3 s relativní hustotou nad 93 %TH. Poslední z prezentovaných materiálů je Ba(Ca)Ti(Zr)O3 bezolovnatá piezokeramika, která byla připravena tuho-fázovou reakcí práškových směsí mletých v planetovém kulovém mlýnu za rozdílných podmínek. Keramická tělesa lisovaná izostatickým tlakem (300 MPa) byla dále zhutněna beztlakým slinováním na teplotách 1200, 1300, 1400 popř. 1500 °C po dobu 1 h na vzduchu. Byly studovány potřebné podmínky pro přípravu jednofázové perovskitové Ba0,85Ca0,15Ti0,9Zr0,1O3 keramiky s požadovanou mikrostrukturou. Úspěšně tak byly připraveny vzorky fázově čisté Ba(Ca)Ti(Zr)O3 keramiky o relativní hustotě až 96 %TH. Prezentované výsledky potvrzují význam volby vhodné metody výroby a potřebných parametrů k získání pokročilých elektrokeramických materiálů s požadovanou mikrostrukturou i fázovým složením a tudíž i pro správné stanovení jejich fyzikálních vlastností.

The requirements of information storage exclusively continue to increase in our daily lives and future, will need even more memory space which should be very small in size but hold the capacity to store a huge volume of information. For that reason, modern research is focusing on molecular memory or optical switches devices where nanoparticles undergoing light-induced transformations (e.g. photodimerization) between structural phases with different optical properties are key components. Hence, the UV reversible photodimerization of the cinnamate groups have the potential to be used as switching segments in optical memory devices. The dissertation deals with the solid state NMR investigation on the influence of alkali cations on the photodimerization of cinnamate salts and cinnamic acid derivatives intercalated in hydrotalcite LDH (layered double hydroxides). The packing of molecules determines reactivity and stereo product, so the motivation is to modify molecular packing through noncovalent interactions by using different cations to influence packing and photodimerization products as well as photodimerization kinetics. The alkali metal salts of m-bromo/chloro cinnamic acid and their photodimerization products are analyzed by solid-state NMR. Cesium, rubidium, and potassium salts show well resolved signals in the 13C CPMAS spectra, whereas for ammonium and sodium salts broader lines are obtained. The size of the cation and with that the packing arrangement in the crystal has a significant influence on the resulting spectra. Cesium, rubidium, and potassium salts photoreact to the corresponding truxinates with a non-planar cyclobutane ring but disorder and lower crystallinity are found in the ammonium and sodium photoproducts. In case of divalent cations, both show good crystal packing in the reactant but Ca di-trans cinnamate shows better photoreaction than Mg di-trans cinnamate. Analysis of the kinetics by the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation shows that the reaction rate is faster with smaller catcationsd in general chlorine salts react faster than the corresponding bromine salts. Furthermore, dethe termination of the chemical shift anisotropy (CSA) tensor for reactant and product provides information for required atomic reorientations in consequence of photoreaction. Results are explained based on these necessary movements of atoms betweethe n reactant and product. Finally, m-bromo cinnamate and K m-bromo cinnamate are successfully incorporated into the LDH to investigate photoreactivity in a confine system. These samples also undergo [2+2] photodimerization upon irradiation with UV light to yield truxinates the , but high degree of disorder in the ipso, cyclobutane and carboxylate spectral region of the photoproduct is found which indicates low crystallinity in both samples.:Bibliographische Beschreibung III Table of contents V List of Figures VII List of Tables XIX Abbreviations XXI 1 Motivation 1 2 Introduction 4 2.1 [2+2] photodimerization of cinnamic acid 5 2.2 Cinnamic acid as optical memory or molecular switches 7 2.3 Layered Double Hydroxide (LDH) 9 2.4 Previous studies of cinnamic acid derivatives by SSNMR 10 3 Experimental 12 3.1 NMR techniques 12 3.1.1 NMR interactions in Solid State NMR 12 3.1.2 Chemical Shift: 13 3.1.3 Dipole-Dipole Interaction: 13 3.1.4 Magic-angle spinning (MAS) 14 3.1.5 Relaxation times 15 3.2 Pulse sequences 16 3.2.1 13C CP (Cross polarization) 16 3.2.2 Dipolar decoupling 17 3.2.3 13C cross polarization dephasing experiment 17 3.2.4 Dipolar coupling 18 3.2.5 2D PASS 19 3.2.6 FSLG 13C-1H CP HETCOR 20 3.3 Typical measurement parameters 20 3.4 Sample preparation 22 3.4.1 Preparation of different cinnamate salt 22 3.4.2 Incorporation of cinnamic compounds into LDH 24 3.5 Sample irradiation by an UV lamp 24 3.6 Computational methods 28 3.7 Single crystal structure data 28 4 Results and discussion 30 4.1 m-Br cinnamate salts of different cations 30 13C CPMAS Spectra of Truxinates 42 Summary 57 4.2 m-Cl cinnamate salts of different cations 57 13C CPMAS Spectra of Truxinates 69 Summary 83 4.3 Influence of divalent cation on cinnamic acid 84 Ca di-trans-cinnamate 84 Mg di-trans-cinnamate 91 Summary 95 4.4 Photoreaction kinetics of cinnamate salts 96 Analysis of reaction kinetics 96 Summary 119 4.5 Intercalation of cinnamic acid derivatives in LDH 120 5 Conclusion 131 6 Outlook 135 7 Appendix 136 8 References 146

O galato de lantânio contendo substituições parciais de estrôncio e magnésio (La1-xSrxGa1-yMgyO3-δ) apresenta estrutura tipo perovsquita e alta condutividade para íons de oxigênio. Outras características desta cerâmica são o extenso domínio eletrolítico e a baixa condutividade eletrônica. É um material promissor para uso como eletrólito sólido em células a combustível de óxido sólido que operam em temperaturas intermediárias, devido sua alta condutividade iônica e estabilidade em uma ampla faixa de pressão parcial de oxigênio. Neste trabalho, a composição La0,9Sr0,1Ga0,8Mg0,2O3-δ foi preparada pelo método convencional de mistura de óxidos a partir de diferentes rotas e pelo método de complexação de cátions. As amostras foram consolidadas pelo método convencional de sinterização e por sinterização rápida. Pelo método de mistura de óxidos foi possível obter a fase ortorrômbica do LSGM, mas não foi possível eliminar as fases SrLaGaO4, La4Ga2O9 e SrLaGa3O7, independente das condições de sinterização utilizadas. Precipitados de óxido de magnésio foram observados nas amostras preparadas pelos dois métodos de síntese empregados identificados apenas por microscopia eletrônica de varredura. As densidades obtidas foram superiores a 97% da densidade teórica em amostras sinterizadas a 1450 °C/4 h, para os materiais preparados por mistura de óxidos. Amostras preparadas por método de complexação de cátions e aquelas consolidadas por sinterização rápida apresentaram menores valores de densidade. Grãos de tamanhos micrométricos foram obtidos para os dois métodos de sinterização. Amostras calcinadas a 1250°C apresentaram maiores densidades e maiores valores de condutividade iônica dos grãos e dos contornos de grãos, quando comparadas com as demais amostras. / Lanthanum gallate with partial substitution on La and Ga sites (La1-xSrxGa1-yMgyO3-δ) has perovskite structure and high oxide-ion conductivity. Other properties of this ceramic material comprise a relatively wide electrolytic domain and low electron conductivity. Doped lanthanum gallate is a potential solid electrolyte for intermediate-temperature solid oxide fuel cells due to its high ionic conductivity and stability in a wide range of oxygen partial pressure. In this work, the composition La0.9Sr0.1Ga0.8Mg0.2O3-δ was prepared by the conventional method of mixing of the starting oxides followed by different processing routes and by the cation complexation method. The ceramic specimens were consolidated by conventional sintering and by fast firing. All specimens prepared by solid state reaction show the characteristic orthorhombic phase of lanthanum gallate and SrLaGaO4, La4Ga2O9 and SrLaGa3O7 secondary phases, independent on the method of sintering. Energy dispersive X-ray spectroscopy coupled to scanning electron microscopy evidenced that all prepared specimens contain MgO grains precipitated along the grain boundaries. High relative densities were obtained for specimens prepared by solid state reaction and consolidated by conventional sintering at 1450 °C/4 h. All specimens exhibit micron sized grains independent on the sintering method. The highest values of relative density and ionic conductivity were obtained for specimens calcined at 1250°C.

Ce travail de thèse s’inscrit dans le cadre de la contribution au programme de valorisation des matériaux phosphatés et plus particulièrement, les phosphates de type alluaudite ou α-CrPO₄. Ces composés se distinguent par leurs propriétés physico-chimiques aussi variées qu’importantes et sont très convoités dans plusieurs domaines d’applications comme la catalyse et l’électrochimie.Nous avons pu isoler onze nouveaux phosphates et déterminer leur structure par la diffraction des rayons X sur monocristal.Le phosphate PbMg₃(HPO₄)(PO₄)₂ a été préparé par la méthode hydrothermale. Sa structure cristalline a été résolue dans le système monoclinique I2/m.La substitution d’un cation Mg²⁺ par un fer trivalent (Fe³) dans le composé PbMg₃(HPO₄)(PO₄)₂ a permis d’isoler cinq nouveaux composés par voie solide. Quatre phosphates de formule MMg₂Fe(PO₄)₃ (M = Ba, Sr, Pb, Ca) s’apparentent à deux types structuraux différents. Les composés contenant Sr et Ba sont de type α-CrPO₄ et cristallisent dans une maille orthorhombique de groupe d’espace Imma. Quant à ceux contenant Ca ou Pb, leur structure s’affine dans le groupe d’espace P21/n du système monoclinique. Le cinquième phosphate est de formule Ca₂MgFe₂(PO₄)₄ cristallisant dans le système monoclinique avec un groupe d’espace Pbca.Enfin, nous avons synthétisé cinq nouveaux phosphates à base de Mg, de Fe et d’élément monovalents : NaMg₃(HPO₄)2(PO₄), Na₂Mg₂Fe(PO₄)₃, Ag₁,₆₇Mg₂,₃₃Fe₀,₈₉(PO₄)₃, Na₁,₈₅Mg₁,₈₅In₁,₁₅(PO₄)₃ et Ag₁,₆₉Mg₁,₆₉In₁,₃₁(PO₄)₃, en utilisant aussi bien la méthode hydrothermale que la synthèse par voie solide. Ces phosphates cristallisent dans le système monoclinique de groupe d’espace C2/c et s’apparentent au type structural alluaudite. La poudre cristalline des phases stoechiométriques A₂Mg₂Fe(PO₄)₃ (A = Na, Ag) a été synthétisée par voie solide et caractérisée par la diffraction de rayons X sur poudre. L’étude de la conductivité en fonction de la température de ces deux composés conduit à σ = 0,12x10⁻⁴ S.cm⁻¹ pour Na₂Mg₂Fe(PO₄)₃ et à σ = 4x10⁻³ S.cm⁻¹ pour Ag₂Mg₂Fe(PO₄)₃ à 500°C. / This study is a part of contribution to the investigation program aiming to elaborate and to characterize new phosphate-based materials, particularly, with the alluaudite and/or α- CrPO₄ type structure. These compounds are characterized by their wide physico-chemical properties that they can exhibit in several fields of application such as catalysis and electrochemistry.We have isolated and determined the structure of eleven new phosphates by means of single crystal X-ray diffraction.The phosphate PbMg₃(HPO₄)(PO₄)₂ was synthesized by hydrothermal method. Its structure was resolved in monoclinic system with space group I2/m.The substitution of one cation Mg²⁺ by Fe³⁺ has allowed us to isolate five new compounds using solid-state diffusion method. Four compounds of general formula MMg₂Fe(PO₄)₃ (M = Ba, Sr, Pb, Ca) exhibit two different structural types. The Sr or Ba based compounds are related to the α-CrPO₄ type structure and crystallize with the space group Imma of the orthorhombic system. Besides, the Ca or Pb based phosphates crystallize with the P21/n space group of the monoclinic system. The fifth phase, namely Ca₂MgFe₂(PO₄)₄, crystallizes in orthorhombic system with a Pbca space group.Finally, we have succeeded to synthesize five new Mg, Fe and monovalent elements based phosphates, namely NaMg₃(HPO₄)₂(PO₄), Na₂Mg₂Fe(PO₄)₃, Ag₁,₆₇Mg₂,₃₃Fe₀,₈₉(PO₄)₃, Na₁,₈₅Mg₁,₈₅In₁,₁₅(PO₄)₃ and Ag₁,₆₉Mg₁,₆₉In₁,₃₁(PO₄)₃, using both the hydrothermal and the solid-state diffusion methods. All these phosphates crystallize in the monoclinic system with C2/c space group and are similar to the alluaudite type structural. The powder of stoichiometric compounds A₂Mg₂Fe(PO₄)₃ (A = Na, Ag) were synthesized by solid-state method and characterized by X-Ray powder diffraction. Conductivity’s studies by impedance spectroscopic method have allowed determining values for Na₂Mg₂Fe(PO₄)₃ (σ = 0.12.10⁻⁴ S.cm⁻¹ at 500°C) and for Ag₂Mg₂Fe(PO₄)₃ (σ = 4.10⁻³ S.cm⁻¹ at 500°C) due to cations migration in the channels of the structure.