Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / A biocerÃmica de hidroxiapatita (HA) Ã um material biocompatÃvel no corpo humano e pode ser uma importante ferramenta em aplicaÃÃes de hipertermia para o tratamento no cÃncer Ãsseo. Neste trabalho investigou-se o efeito da adiÃÃo de Ãons de ferro na estrutura da HA com o objetivo de obter uma biocerÃmica que venha ser utilizado no tratamento hipertÃrmico contra o cÃncer. As amostras foram preparadas pelo mÃtodo cerÃmico e caracterizadas pela difraÃÃo de raios-X, espectroscopia do infravermelho (FTIR), microdureza Vickers, medidas elÃtricas (constante e perda dielÃtrica) e microscopia eletrÃnica de varredura (MEV). AtravÃs da difraÃÃo de raios-X verificou-se a presenÃa da fase Ca2Fe2O5 que apresenta uma estrutura denominada Brownmillerite. Verificou-se melhoria das propriedades mecÃnicas e elÃtricas com o aumento da temperatura de sinterizaÃÃo. Observou-se que o aumento da concentraÃÃo de ferro e da temperatura de sinterizaÃÃo ocasionaram mudanÃas morfolÃgicas nos grÃos. / The bioceramic called hydroxyapatite (HA) is a biocompatible material which can be an important tool in hyperthermia applications for the treatment of bony cancer. In this work the effect of the addition of Fe ions in the structure of the HA was investigated with the objective of obtaining a magnetic bioceramic to be used in the hyperthermic treatment against the cancer. The samples were prepared by the ceramic method and characterized by the X-ray diffraction (XRD), infrared spectroscopy (FTIR), Vickers hardness, electric properties (constant and loss dielectric) and scanning electronic microscopy (SEM). The presence of the phase Ca2Fe2O5 was verified by X-ray diffraction analysis, showing a structure Brownmillerite. The improvement of the mechanical and electric properties was verified with the increase of the sintering temperature. It was observed that the increase of the Fe addition and the sintering temperature caused morphologic changes in the grains.

Les conducteurs d'ions oxygène fonctionnant à des températures inférieures à 300 ° C sont des matériaux d'intérêt majeur pour une série d’applications technologiques telles que les piles à combustible solide, les batteries, les électrodes, les capteurs, des catalyseurs, etc. Cependant à l’heure actuelle, les conducteurs d'ions d'oxygène solides fonctionnent raisonnablement seulement à haute température, supérieure à 800°C, ce qui limite leur application. Dans la recherche de l'amélioration des conducteurs d'ions d'oxygène, la structure Brownmillérite (ABO2.5 éq. A2B2O5) a toujours joué un rôle important, en particulier dans le régime à basse température où la dynamique de la chaîne tétraédrique induit la mobilité de l'oxygène. Dans ce contexte, nous avons synthétisé une nouvelle phase Sr2-xBaxScGaO5 (avec x=0 SSGO et x= 0.1 SBSGO), contenant des ions 3d0 diamagnétiques et susceptible d’être un conducteur ionique pur. En fonction de la voie de synthèse, le composé présente deux polymorphes, orthorhombiques et cubiques, qui sont tous deux importants pour la conductivité de l'oxygène. La réaction à l’état solide conduit à une structure de type Brownmillerite orthorhombique tandis que la synthèse de fusion de zone (FTZ) donne une structure Pérovskite déficitaire en oxygène .Par diffraction neutronique sur poudre (D2B @ ILL) nous avons analysé la structure des deux polymorphes, en fonction de la température. Une analyse détaillée du type SSGO Brownmillerite montre que le Sc occupe les sites octaédriques, tandis que Ga occupe exclusivement les tétraèdres autres. Cet ordre de cations est assez inhabituel pour les structures de type Brownmillerite. La deuxième particularité est que Sr2-xBaxScGaO5 subit une transition de phase à partir d'une configuration ordonnée des chaines (GaO4), caractéristiques du groupe d’espace I2mb à température ambiante, vers une configuration désordonnée des chaînes dans le groupe d’espace Imma (à 500°C). Ce résultat important confirme notre hypothèse que le désordre est dynamique et il est la clé pour avoir un conducteur d'ions d'oxygène à températures modérées. La synthèse à des températures élevées (jusqu'à fusion), donne une structure cubique Pm ̅m, stable jusqu'à 1000 ° C. La structure est de type Pérovskite fortement déficitaire en oxygène. La mobilité de l’oxygène de ces nouveaux composés a été ensuite étudiée par la thermogravimétrie (TGA) couplée avec spectroscopie de masse (MS) après échange isotopique 18O-16O, par spectroscopie RAMAN et RMN couplée avec les calculs théoriques ab-initio (WIEN2k), par diffusion inélastique des neutrons (IN6@ILL) couplée avec des calculs de dynamiques moléculaire ab-initio (VASP). Les résultats obtenus via les études structurales et de dynamique de réseau montrent que l’activation de la mobilité ionique est liée à la transition vers la structure désordonnée Imma, qui implique une dynamique importante des chaines GaO4 et une diffusion unidimensionnel le long des canaux lacunaires. Ces résultats ont pu être reproduits par calculs de dynamique moléculaire, dans lesquels la diffusion ne concerne que les oxygènes des plans tétraédriques, et s’expliquent par des paramètres de maille a et c qui sont significativement augmentés par rapport à (Ca/Sr)FeO2.5. / Oxygen ion conductors operating at low temperature, below 300 ° C, are materials of major interest for several applications in the area of solid state ionicsas solid fuel cells, batteries, electrodes, sensors, catalysts, etc. However till now, the solid oxygen ion conductor works reasonably only at high temperatures above 800 ° C, which limits their application. In the search for improved oxygen ion conductors Brownmillerite structures ( ABO2.5 eq. A2B2O5 ) has always played an important role, especially in the low temperature regime where the dynamics of the tetrahedral chain induced mobility of oxygen. In this context, we have synthesized a new phase Sr1-xBaxScGaO5 with x = 0 (SSGO) and x = 0.1 (SBSGO) containing diamagnetic 3d0 ions to have a pure ion conductor. Depending on the synthesis route, the compound has two polymorphs, orthorhombic and cubic, which are both important for the oxygen conductivity. The reaction in the solid state leads to an orthorhombic Brownmillerite-type structure, while tmeling synthesis (using the Travelling Floating Zone method FTZ ) gives an oxygen-deficient Perovskite structure. The structures of both polymorphs were analyzed using the neutron powder diffraction as function of the temperature (D2B@ILL). A detailed analysis of SSGO Brownmillerite type shows that the Sc occupies octahedral sites, while the Ga occupies exclusively the tetrahedral ones. This cation ordering is unusual for the Brownmillerite structures. Moreover Sr2-xBaxScGaO5 undergoes a phase transition from an ordered configuration of the tetrahedral chains (GaO4) characteristic of I2mb space-group at room temperature, toward a disordered one characteristic of Imma space group (500 ° C). This important result confirms that the disorder of the tetrahedral chains is dynamic and it is the key to have oxygen ion conductor at moderate temperatures. Synthesis at elevated temperatures (up to melting point) gives a cubic structure Pm ̅m, stable up to 1000 ° C. The Perovskite -type structure is highly oxygen deficient. The mobility of the oxygen of these new compounds was studied by thermogravimetry analysis (TGA) coupled with mass spectrometry (MS) after the isotope exchange 18O-16O, by Raman and NMR spectroscopy coupled with theoretical ab-initio calculations (WIEN2k), by inelastic neutron scattering (IN6@ILL) coupled with calculations of ab-initio molecular dynamics (VASP ) . The results obtained from the structural and the lattice dynamics studies show that activation of the ion mobility is related to the transition to a disordered structure Imma, which implies an important dynamics of the chains GaO4 and the diffusion along the one-dimensional vacancy channel. These results have been reproduced by molecular dynamics calculations, in which the diffusion pathway is due only to the oxygen in the tetrahedral planes.

Transition metal oxides exhibit potential in various application fields due to the special d-electrons. Solid state chemistry focuses on discovering the structure-property relationships. The work in this thesis mainly discusses compounds with hexagonal or brownmillerite-type structure and their practical properties. Hexagonal YIn[subscript 1-x]Fe[subscript x]O��� (x = 0-0.3, 0.7-1.0) phases have been prepared and characterized. All phases appear to have the ferroelectric structure known for YInO���. The color of the phases changes from yellow to orange to dark red with increasing Fe content. Magnetic measurements confirm high-spin Fe����� for all phases. Similarly, solid solution YAl[subscript 1-x]Fe[subscript x]O��� (x = 0-0.4, 0.7-1.0) phases were successfully synthesized through the sol-gel method. The Al-rich compounds present paraelectric YAlO��� structure while the Fe-rich side samples exhibit YFeO��� structure. The color of the compounds appear to be yellow with small Fe content and change to brown which has higher Fe content. Brownmillerite-type oxides Ba���In[subscript 2-x]Mn[subscript x]O[subscript 5+x] (x = 0.1-0.7) have been prepared and characterized. Magnetic measurements confirm that Mn in as prepared samples is substituting as Mn������ for all values of x with observed paramagnetic spin-only moments close to values expected for two unpaired electrons. Neutron diffraction structure refinements show Mn������ occupies tetrahedral sites for orthorhombic (x = 0.1) and tetragonal (x = 0.2) phases. For Mn ��� 0.3 samples, neutron refinements show the phases are cubic with disordered cations and oxygen vacancies. The colors of the phases change from light yellow (x = 0) to intense turquoise (x =0.1), to green (x = 0.2, 0.3) or dark green (x ��� 0.4). Solid solution Ba���In[subscript 2-x]Fe[subscript x]O[subscript 5+y] (x = 0.1-1.5) also exhibit brownmillerite-type structure. The color of the compounds appear to be green with small Fe content and change to black with higher Fe content (x ��� 0.3). Magnetic measurements and M��ssbauer spectroscopy conclude the mixed valence of Fe�����/Fe������ for all the phases. Nonstoichiometry compound YCu���.���Ti���.���O[subscript 3-��] has been prepared and characterized. Structure study indicates that oxygen vacancy is favored under the synthesis condition. This change in oxygen content was further studied in the Mn-doped system. And the effect of stoichiometric difference in the Mn-doped samples was not as obvious as the initial compound. The disorder in the cation site enhanced the tolerance of the structure in the aspect of oxygen content. The hexagonal phases LnCu���.���Ti���.���O��� (Ln = Y, Tb-Lu) phases were prepared by the traditional solid state reactions. The prepared compounds were reduced at high temperature in the reduction atmosphere created by the H���/N��� gas mixture. Study on the structure and properties changes by reduction was conducted by X-ray diffraction, optical measurement, magnetic measurement and thermalgravimetric analysis. And we observed some evidence of the presence of Cu��� in the reduced phase by these characterization methods. Solid solution YMn[subscript x]Ti[subscript y]O[subscript 3-��] (y = 0.1-0.4) was successfully prepared through conventional solid state approach. All the samples showed hexagonal structure. But the structure transition from ferroelectric P6���cm to paraelectric P6���/mmc occurred when Ti amount is higher than 0.2. Based on the neutron diffraction refinement, the lattice expanded in the ab plane but contracted along the c axis direction. / Graduation date: 2013

<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)