Дисертації з теми "Perovskite to post-perovskite phase transition"
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Chu, Fan. "The ferroelectric phase transition in complex perovskite relaxors /." [S.l.] : [s.n.], 1994. http://library.epfl.ch/theses/?nr=1248.
Повний текст джерелаQasim, Ilyas. "Structural and Electronic Phase Transitions in Mixed Transition Metal Perovskite Oxides." Thesis, The University of Sydney, 2013. http://hdl.handle.net/2123/10029.
Повний текст джерелаParisi, Filippo. "A Bader’s topological approach for the characterization of pressure induced phase transitions." Doctoral thesis, Università degli studi di Trieste, 2012. http://hdl.handle.net/10077/7420.
Повний текст джерелаIn questo lavoro è stata messa a punto una metodologia basata sull’analisi topologica della densità elettronica secondo la teoria di Bader che ha permesso di indagare la stabilità di fasi mineralogiche in condizioni di alta pressione. In una prima fase è stata caratterizzata la decomposizione della ringwoodite (olivina-γ) in Mg-perovskite e periclasio ( post spinel phase transition) che si ritiene essere responsabile della discontinuità sismica che si osserva a 660 Km di profondità, tra la zona di transizione del mantello ed il mantello inferiore. Lo scopo del lavoro è stato quello di ottenere informazioni sulla disposizione degli elettroni nella struttura cristallina e sulla evoluzione al variare delle condizioni di pressione. L’analisi effettuata ha mostrato l’instaurarsi di una forte instabiltà strutturale (caratterizzata da una “conflict catastrophe”) nella ringwoodite a circa 30 GPa. Tale risultato conferma il coinvolgimento della transizione di fase “post-spinel”nella discontinuità sismica a 660 Km. In una seconda fase la procedura è stata applicata alla fase Mg-perovskite allo scopo di testarne la validità. Lo studio dell’evoluzione della topologia della densità elettronica nel range di pressione da 0 a 200 GPa ha permesso di individuare una regione di stabilità della fase perovskitica (da circa 22 a circa 124 GPa) delimitata tra due “fold catastrophes”. Le due “fold catastrophes” si hanno entrambe in prossimità di discontinuità sismiche: la prima, attribuita alla transizione di fase da ringwoodite a Mg-perovskite + periclasio corrisponde alla discontinuità sismica a 660 Km e la seconda, attribuita alla transizione da Mg-perovskite a post-perovskite a circa 130 GPa, osservata a circa 2600 Km di profondità, tra il mantello profondo e il D′′-layer, poco prima della discontinuità di Gutemberg a 2900 Km.
XXIV Ciclo
1975
Ruette, Benjamin Thibault. "Induced Phase Transition in Magnetoelectric BiFeO3 Crystals, Thin-layers and Ceramics." Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/42638.
Повний текст джерелаMaster of Science
Yang, Zhuo. "Investigation of the excitonic properties of hybrid and fully inorganic perovskite using magneto-spectroscopy." Thesis, Toulouse, INSA, 2018. http://www.theses.fr/2018ISAT0004/document.
Повний текст джерелаOptical and electronic properties. The photon conversion efficiency of hybrid perovskite based solar cells has increased from 6.9% to 23.6% within the last few years. The aim of this thesis is to investigate the optical and electronic properties of perovskite materials using magneto-optical techniques. We have investigated the relationship between the excitonic properties and the microstructure of hybrid perovskites. We have performed magneto-transmission measurement on MAPbI3 polycrystalline thin films and magneto-reflectivity measurement on a MAPbI3 single crystal. We find that, at low temperature, the exciton binding energy and reduced mass are the same for all MAPbI3 samples with a variety of crystal grain sizes.We have also investigated the electronic properties of the fully inorganic perovskites, namely CsPbX3 compounds (X = I or Br or a mixture of those). By performing the magneto-transmission measurement on CsPbX3, we have determined the exciton binding energies and reduced mass with high accuracy. A comparison of the values of dielectric constant for the fully inorganic and the hybrid organic-inorganic perovskites indicates that, at low temperature when the organic cations are frozen, the dominant contribution to the dielectric screening is related to the relative motion within the lead halide cage
Gunatilleke, Wilarachchige D. C. B. "Analysis and New Applications of Metal Organic Frameworks (MOF): Thermal Conductivity of a Perovskite-type MOF and Incorporation of a Lewis Pair into a MOF." Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7514.
Повний текст джерелаJoo, Gi-Tae. "Nouvelles phases ferroélectriques non stoechiométriques de type perovskite ou LiTaO3." Phd thesis, Université Sciences et Technologies - Bordeaux I, 1986. http://tel.archives-ouvertes.fr/tel-00203505.
Повний текст джерелаWang, Di. "Some Aspects of the Crystal Chemistry of Perovskites under High Pressures." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/37733.
Повний текст джерелаPh. D.
Berini, Bruno. "Elaboration de couches minces de SmFeO3 et LaNiO3, de structure perovskite, par dépôt laser pulséEtudes associées des transitions de phase à haute température par ellipsométrie spectroscopique in situ." Phd thesis, Université de Versailles-Saint Quentin en Yvelines, 2007. http://tel.archives-ouvertes.fr/tel-00243093.
Повний текст джерелаL'étude s'est d'abord focalisée sur la croissance du SFO sur silice amorphe afin de déterminer les conditions de croissance. Les épaisseurs sont mesurées in situ pendant la croissance par ellipsométrie spectroscopique. La variation thermique des indices optiques ainsi que les paramètres de maille présentent deux transitions qui semblent être corrélées aux températures de Curie (Tc) et de réorientation de spin (TRS). Une croissance épitaxiale du SFO (cube sur cube) sur STO (001) a été aussi obtenue. Les mesures magnétiques à l'ambiante (SQUID) montrent que les moments magnétiques pointent dans la direction perpendiculaire au film, c'est à dire suivant c, axe de facile aimantation à haute température (T> TRS) contrairement aux prévisions (axe a).
Une optimisation des températures de substrat et de pression d'oxygène a été ensuite réalisée lors de la croissance épitaxiale (cube sur cube) du LNO sur STO (001). La variation thermique des indices optiques, linéaire, présente un changement de pente dans la gamme [200-300°C]. L'ellipsométrie permet également la détection des transitions métal-isolant associées à la réduction et ré-oxygénation des films. La cinétique de la ré-oxygénation est détaillée ainsi que le contrôle de l'état d'oxydation.
Enfin, nous avons étudié les hétérostructures SFO/LNO/STO et SFOII/LNOII/SFOI/LNOI /STO. Nous avons montré que SFO croit de manière épitaxiale (cube sur cube) sur LNO. L'influence des épaisseurs de SFO et de LNOII sur les propriétés de transport à basse température des empilements est finalement démontrée.
Madon, Michel. "Cellules à enclumes de diamant et microscopie électronique en transmission : étude expérimentale des transformations de phase du manteau terrestre." Paris 6, 1986. http://www.theses.fr/1986PA066123.
Повний текст джерелаBerini, Bruno. "Elaboration de couches minces de SmFeO3 et LaNiO3, de structure perovskite, par dépôt laser pulsé : études associées des transitions de phase à haute température par ellipsométrie spectropique in situ." Versailles-St Quentin en Yvelines, 2007. http://www.theses.fr/2007VERS0024.
Повний текст джерелаThis work presents the growth of SmFeO3 (SFO) and LaNiO3 (LNO) thin films by pulsed laser deposition. First, we have focused on deposition conditions of SFO growth on fused quartz substrate. Thicknesses have been calculated from in situ ellipsometric measurements during the growth. Furthermore, optical indexes and lattice parameters show two transition temperatures in correlation with the Curie (Tc) and spin reorientation (TRS) temperatures. Epitaxial cube on cube growth has been obtained on SrTiO3 (STO) (001). In this case, the easy magnetization axis, as measured by SQUID magnetometry, is perpendicular to the film plane at room temperature whereas it is expected to be along the a direction. Second, substrate temperatures and oxygen pressures have been varied to determine the optimal deposition conditions for epitaxial cube on cube growth of LNO films on STO (001) substrate. The thermal variation of optical indexes is linear with a change in the slope around [200-300°]. In situ spectroscopic ellipsometry is used, as well, for the detection of the metal-insulator transition associated with the reduction and re-oxygenation of thin films. The kinetics of this last transformation are detailed and we show that it's possible to tune of the oxidation state. Finally, SFO/LNO/STO and SFOII/LNOII/SFOI/LNOI/STO heterostructures have been made. Again, the growth of SFO on LNO is epitaxial (cube on cube). Transport measurements have revealed an effect of both SFO and LNOII thicknesses at low temperature and are discussed here
Magyari-Köpe, Blanka. "Structural stability of solids from first principles theory." Doctoral thesis, KTH, Physics, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3366.
Повний текст джерелаLangrand, Christopher. "Étude expérimentale et in situ du mécanisme de transformation perovskite / post-perovskite et de sa cinétique dans le manteau terrestre." Thesis, Lille 1, 2017. http://www.theses.fr/2017LIL10157/document.
Повний текст джерелаThe radial seismic structure of the earth is marked by a sharp transition about 200 km above the core-mantle boundary. This defines the top of the region called the D'' layer. Moreover, at these P/T conditions, Bridgmanite (Pv), the main lower mantle mineral, transforms into its high-pressure phase, (Mg,Fe)SiO3 post-perovskite (pPv). This phase transition has received considerable interest due to its thermodynamic properties, the induced textures and microstructures that seem to explain many of the seismic anomalies of the D'' layer. However, its thermodynamic properties and transformation mechanisms are not very well known. The main purpose of this thesis was to investigate the Pv/pPv phase transition and its kinetics. To do so, we used a novel method, called Multigrain Crystallography, to characterize in-situ hundreds of crystals in a polycrystalline material. The reliability of the method for experiments under extreme conditions is tested in the first part of this manuscript. I then focus on the Pv/pPv phase transition mechanism on a structural analog of composition NaCoF3. I determine that the Pv to pPv transformation is martensitic and that the reverse transformation is reconstructive. Their impacts on the D'' layer microstructure are also discussed. Finally, I explore the kinetics of the (Mg0,86,Fe0,14)SiO3 Pv to pPv transition by time-series experiments. Moreover, based on our data, I present two possible kinetic models that include the effect of pressure, temperature, and grain size. These models have important implications to constrain the dynamics and kinetics of the Bridgmanite to pPv transition at the D'' layer P/T conditions
Derenne, Sylvie. "Contribution a l'etude des proprietes physiques de mineraux du manteau inferieur." Paris 6, 1988. http://www.theses.fr/1988PA066281.
Повний текст джерелаKhan, Hidayat Ullah. "Phase transitions in Li-doped Ag(NbxTa₁-x)O₃ perovskite ceramics." Thesis, University of Sheffield, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.557952.
Повний текст джерелаQu, Weiguo. "In-situ TEM investigation of the phase transitions in perovskite ferroelectrics." [Ames, Iowa : Iowa State University], 2008.
Знайти повний текст джерелаChapman, Brandon D. "The role of disorder in structural phase transitions in perovskite ferroelectrics /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/9692.
Повний текст джерелаReynolds, Emily Maria. "Structure-property relationships of uranium and technetium-containing oxides." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/15956.
Повний текст джерелаWhittle, Thomas Anthony. "A Structural Investigation of Perovskite and Tungsten Bronze Type Ferroic Materials." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/14586.
Повний текст джерелаJoo, Gi-Tae. "Nouvelles phases ferroélectriques non-stœchiométriques de type perovskite ou LiTaO₃." Bordeaux 1, 1986. https://tel.archives-ouvertes.fr/tel-00203505.
Повний текст джерелаRavel, Bruce D. "Ferroelectric phase transitions in oxide perovskites studied by XAFS /." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/9784.
Повний текст джерелаTrotsenko, Vasily. "Couplage magnéto-électrique dans des ferrites et des manganites de structure perovskite." Thesis, Amiens, 2018. http://www.theses.fr/2018AMIE0011.
Повний текст джерелаThe aim of the present thesis is to study the lattice dynamics of ferrites Bi1-xAxFeO3 (A= Sr, Ca) and manganites La1-хСахМnОЗ and Pr1-хCaхMnO3 systems subject of competitive electric and magnetic order parameters. To identify the microscopic mechanisms of both magnetic and electric ordering in these systems, usual x-ray diffraction study has been conducted to highlight the effect of aliovalent substitution on the structural changes. The evolution of crystal symmetry was found to depend not only to the concentration of substituting element but also to its nature (Sr or Ca). Raman and infrared and of sub-THz, Mössbauer, and XPS were used as appropriate spectroscopic techniques for studying the lattice excitations in the studied systems where polar and magnetic orders expected to coexist. In order to shed more light on strain- and size effects on the microscopic mechanisms of both magnetic and electric ordering in the same phase, epitaxial films of some selected phase were grown by pulse laser deposition on SrTiO3(STO), MgO, and MgO buffered STO substrates. Our results confirm the coexistence of charge–ordered antiferromagnetic state and ferromagnetic metallic phases with the competition between super-exchange and double-exchange interactions. In this work, the conditions of coexistence of magnetic and electric structures were found to depend on the cation substitutions as well as on the method of sample elaboration either in ceramics or in thin films forms
Schmidt, Marek Wojciech, and Marek Schmidt@rl ac uk. "Phase formation and structural transformation of strontium ferrite SrFeOx." The Australian National University. Research School of Physical Sciences and Engineering, 2001. http://thesis.anu.edu.au./public/adt-ANU20020708.190055.
Повний текст джерелаCastro, Junior Manoel Carvalho. "Transições de fase em perovskitas politípicas." reponame:Repositório Institucional da UFC, 2013. http://www.repositorio.ufc.br/handle/riufc/13878.
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In this thesis, vibrational spectroscopy was used to investigate the structural transitions of polytypic perovskites. Representative compounds of two polytypes were studied: the multiferroic 3C-type perovskite Pb(Fe1/2Nb1/2)O3 (PFN) and the 6H-type perovskites Ba3B2+Sb2O9 (B = Mg, Ca e Sr). Based on anomalies or deviations from normal behavior of the adjustable parameters of the temperature dependence of the phonon spectra of these compounds, it was possible to identify structural transformations. In PFN, it was observed, evidences of two transitions between ferroelectric phases, in addition to a transition between different magnetic ordering states (paramagnetic → antiferromagnetic) and different polar states (paraelectric → ferroelectric). These results provide stronger evidences than previous Raman Spectroscopy reports in literature due to a better resolution, which allowed us to observe, for example, a new phonon at the Néel temperature. In the case of the 6H perovskites, besides to the usual observation of temperature dependence of the phonon spectra, which provides evidences of the transition of a hexagonal to monoclinic phase at 140 K in the Ba3MgSb2O9 (BMS) and of a monoclinic to triclinic phase at 240 K in the Ba3MgSb2O9 (BCS), we classify the phonons of the three compounds using two methods. First we applied the Hartree-Fock ab-initio method to calculate the normal modes of the Sb2O9 dimer; and assuming that the unit cell of BMS is constituted of Sb2O9 dimers and isolated ions of Ba and Mg, we correlate, using group theory methods, the calculated modes of Sb2O9 with the internal modes of BMS. Later we used the FG Wilson method to confirm the previous results, being obtained a good agreement between the two methods.
Nesta tese a espectroscopia vibracional foi empregada para investigar as transições estruturais de perovskitas politípicas. Compostos representativos de dois polítipos foram estudados: a perovskita multiferróica tipo 3C Pb(Fe1/2Nb1/2)O3 (PFN) e as perovskitas tipo 6H Ba3B2+Sb2O9 (B = Mg, Ca e Sr). A partir de anomalias ou desvios do comportamento normal dos parâmetros ajustáveis com a temperatura do espectro de fônons destes compostos foram identificadas transformações estruturais. No PFN foram observados indícios de duas transições entre fases ferroelétricas, além de uma transição entre diferentes fases de ordenamento magnético (estado paramagnético → estado antiferromagnético) e uma transição entre um estado paraelétrico e um ferroelétrico. Estes resultados são expostos de forma bem mais clara do que em trabalhos de espectroscopia Raman anteriormente informados na literatura, devido a melhor resolução obtida, o que propiciou até a observação da origem de um novo modo no entorno da temperatura de Néel. Nas perovskitas 6H, além da observação usual do comportamento dos fônons em função da temperatura, o que rendeu a observação da transição de uma fase hexagonal para uma fase monoclínica em 140K no Ba3MgSb2O9 (BMS) e de uma fase monoclínica para uma fase triclínica em 240 K no Ba3MgSb2O9 (BCS), procurou-se classificar os fônons dos três compostos utilizando dois métodos computacionais. Primeiramente utilizou- se o método ab initio de Hartree-Fock para calcular os modos normais do dímero Sb2O9; e assumindo que a célula unitária do BMS é formada de dímeros Sb2O9 e íons isolados de Ba e Mg, conseguiu-se correlacionar, utilizando teoria de grupos, os modos calculados do Sb2O9 com os modos internos do BMS. Posteriormente utilizou-se o método FG de Wilson para corroborar os resultados anteriormente obtidos, sendo observado um bom acordo entre ambos métodos.
Jones, Glyn Owen. "Investigation of the structure and phase transitions in the novel A-site substituted perovskite series (Na1-xKx)0.5Bi0.5TiO." Thesis, University of Warwick, 2001. http://wrap.warwick.ac.uk/4032/.
Повний текст джерелаBecker, Pascal [Verfasser]. "Structural and Optoelectronic Properties, Phase Transitions, and Degradation of Semiconducting CsPbI3-Perovskite Thin-Films for Photovoltaics / Pascal Becker." Wuppertal : Universitätsbibliothek Wuppertal, 2019. http://d-nb.info/120422255X/34.
Повний текст джерелаJunior, Manoel Carvalho Castro. "TransiÃÃes de fase em perovskitas politÃpicas." Universidade Federal do CearÃ, 2013. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=10160.
Повний текст джерелаNesta tese a espectroscopia vibracional foi empregada para investigar as transiÃÃes estruturais de perovskitas politÃpicas. Compostos representativos de dois polÃtipos foram estudados: a perovskita multiferrÃica tipo 3C Pb(Fe1/2Nb1/2)O3 (PFN) e as perovskitas tipo 6H Ba3B2+Sb2O9 (B = Mg, Ca e Sr). A partir de anomalias ou desvios do comportamento normal dos parÃmetros ajustÃveis com a temperatura do espectro de fÃnons destes compostos foram identificadas transformaÃÃes estruturais. No PFN foram observados indÃcios de duas transiÃÃes entre fases ferroelÃtricas, alÃm de uma transiÃÃo entre diferentes fases de ordenamento magnÃtico (estado paramagnÃtico → estado antiferromagnÃtico) e uma transiÃÃo entre um estado paraelÃtrico e um ferroelÃtrico. Estes resultados sÃo expostos de forma bem mais clara do que em trabalhos de espectroscopia Raman anteriormente informados na literatura, devido a melhor resoluÃÃo obtida, o que propiciou atà a observaÃÃo da origem de um novo modo no entorno da temperatura de NÃel. Nas perovskitas 6H, alÃm da observaÃÃo usual do comportamento dos fÃnons em funÃÃo da temperatura, o que rendeu a observaÃÃo da transiÃÃo de uma fase hexagonal para uma fase monoclÃnica em 140K no Ba3MgSb2O9 (BMS) e de uma fase monoclÃnica para uma fase triclÃnica em 240 K no Ba3MgSb2O9 (BCS), procurou-se classificar os fÃnons dos trÃs compostos utilizando dois mÃtodos computacionais. Primeiramente utilizou- se o mÃtodo ab initio de Hartree-Fock para calcular os modos normais do dÃmero Sb2O9; e assumindo que a cÃlula unitÃria do BMS à formada de dÃmeros Sb2O9 e Ãons isolados de Ba e Mg, conseguiu-se correlacionar, utilizando teoria de grupos, os modos calculados do Sb2O9 com os modos internos do BMS. Posteriormente utilizou- se o mÃtodo FG de Wilson para corroborar os resultados anteriormente obtidos, sendo observado um bom acordo entre ambos mÃtodos.
In this thesis, vibrational spectroscopy was used to investigate the structural transitions of polytypic perovskites. Representative compounds of two polytypes were studied: the multiferroic 3C-type perovskite Pb(Fe1/2Nb1/2)O3 (PFN) and the 6H-type perovskites Ba3B2+Sb2O9 (B = Mg, Ca e Sr). Based on anomalies or deviations from normal behavior of the adjustable parameters of the temperature dependence of the phonon spectra of these compounds, it was possible to identify structural transformations. In PFN, it was observed, evidences of two transitions between ferroelectric phases, in addition to a transition between different magnetic ordering states (paramagnetic → antiferromagnetic) and different polar states (paraelectric → ferroelectric). These results provide stronger evidences than previous Raman Spectroscopy reports in literature due to a better resolution, which allowed us to observe, for example, a new phonon at the NÃel temperature. In the case of the 6H perovskites, besides to the usual observation of temperature dependence of the phonon spectra, which provides evidences of the transition of a hexagonal to monoclinic phase at 140 K in the Ba3MgSb2O9 (BMS) and of a monoclinic to triclinic phase at 240 K in the Ba3MgSb2O9 (BCS), we classify the phonons of the three compounds using two methods. First we applied the Hartree-Fock ab-initio method to calculate the normal modes of the Sb2O9 dimer; and assuming that the unit cell of BMS is constituted of Sb2O9 dimers and isolated ions of Ba and Mg, we correlate, using group theory methods, the calculated modes of Sb2O9 with the internal modes of BMS. Later we used the FG Wilson method to confirm the previous results, being obtained a good agreement between the two methods.
Roukos, Roy. "Transitions de phases dans des oxydes complexes de structure pérovskite : cas du système (1-x)Na0,5Bi0,5TiO3 - xCaTiO3." Thesis, Dijon, 2015. http://www.theses.fr/2015DIJOS020/document.
Повний текст джерелаThe solid solutions (1-x)Na0,5Bi0,5TiO3 (NBT) – xCaTiO3 (CT) were studied by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, impedance spectroscopy and DSC. These materials have a perovskite crystalline structure. This study reveals not only the complexity but also the richness of physical phenomena in these compounds: phases transitions sequences, the Ca2+ effect on the physical-chemistry properties and the relation between dielectric properties and crystalline structure. Thereby, (1-x)NBT – xCT solid solutions (0 ≤ x ≤ 1.00) were synthesized by chemical solid route, then they were sintered by a particular procedure in order to avoid sodium and bismuth volatilization. The solid crystalline characteristics obtained prove clearly the necessity to distinguish three fields as a function of x values. First of all, for increasing x at room temperature, there is a first region so called region I (x ≤ 0.07), wherein the crystalline structure of solid solutions obtained has a space group R3c identical to that of pure NBT. For the highest values of x, (Region II, x ≥ 0.15), the solid obtained has a space group Pnma, identical to that of pure CT. Finally, between these two regions, (0.09 ≤ x ≤ 0.13), the solid solutions obtained are biphasic, R3c + Pnma, limited to appellations of the space groups formed phases. In region I, upon heating, phase transition sequence R3c → R3c + Pnma → Pnma was determined; the corresponding transition temperatures move to low values with increasing Ca2+ concentration. These solids are ferroelectric at room temperature and then develop a relaxor character, by coexistence of two phases, with increasing temperature. In region II, these solids reveal a relaxor behavior at room temperature. However, a diffuse phase transition within the orthorhombic phase Pnma has been identified; the solid changes from relaxor to paraelectric while maintaining the same crystal structure. This phenomenon was explained by the formation of micro or nano-polar regions. Region III, demonstrated for the first time, is characterized by thermal hysteresis, and explained by the relation between crystalline microstructure and dielectric properties. Finally, all our results were assembled in an original phase diagram as a function of concentration of Ca2+ dopant and temperature
Barbosa, Quiroga David Antonio. "Processamento e propriedades do sistema ferroelétrico livre de chumbo (Bi, Na)TiO3 (Bi, K)TiO3 BaTiO3." Universidade Federal de São Carlos, 2015. https://repositorio.ufscar.br/handle/ufscar/5075.
Повний текст джерелаFinanciadora de Estudos e Projetos
In this work, the lead-free ceramic powders of xBi0,5Na0,5TiO3 - (0,7186 - 0,7143x) Bi0,5K0,5TiO3 - (2814 - 2857x) BaTiO with x = 0,8200; 0,8625; 0,8792, 0,9126 and 0,9300 (BNBK1000x) were prepared by the solid state reaction method, followed by conventional densification. The ceramic bodies showed high density, which was higher than 95% in obtained samples. For the all ceramics were performed structural, micro structural, electric and anelastic characterizations. The X-ray diffraction (XRD) analysis indicated the formation of the complex perovskite type crystaline structure for all compositions analyzed without the presence of spurious phases. By the structural refinement by the Rietveld method of XRD data and by Raman spectroscopy were observed that for BNBK912 and BNBK930 compositions, at room temperature, the predominant symmetry is rhombohedral (R3c), while the BNBK820 composition exhibits a tetragonal crystalline symmetry (P4mm). For the BNBK879 and BNBK826 compositions presented a mixture of phases, possibly with rhombohedral and tetragonal symmetry, reaveling the morphotropic phase boundary (MPB) of this system. The microstructure of BNBK1000x ceramics was investigated by scanning electron microscopy (SEM), where the morphology grains with irregular sizes and shapes, where the increased levels of K+ and Ba2+ ions suppressed the growth of the grains. The characterizations by Raman spectroscopy at room temperature showed broad Raman modes, due to the chemical and/or structural disorder related to the substitution of elements Bi and Na for Ba and K. The ferroelectric characterizations at room temperature of the BNBK1000x ceramics showed that all compositions studied are ferroelectric. Through the comparison among the measurements of electrical impedance and mechanical spectroscopy, was possible to identify the different structural and electric phase transitions that were employed in the construction of a pseudodiagram of phases for the BNBK1000x compositions.
Neste trabalho, os pós-cerâmicos livres de chumbo xBi0,5Na0,5TiO3 - (0,7186 - 0,7143x) Bi0,5K0,5TiO3 - (2814 - 2857x) BaTiO com x = 0,8200; 0,8625; 0,8792, 0,9126 e 0,9300 (BNBK1000x) foram obtidos através do método de reação de estado sólido, seguido por densificação convencional. Os corpos cerâmicos obtidos apresentaram elevada densificação, sendo maior que 95% nas amostras produzidas. Para todas as cerâmicas foram realizadas caracterizações estruturais, microestruturais, elétricas e anelásticas. As análises por difração de raios-X (DRX) indicaram a formação da estrutura cristalina tipo perovkista complexa para todas as composições analisadas, sem a presença de fases espúrias. O refinamento estrutural, pelo método de Rietveld, dos resultados de DRX e os resultados de espectroscopia Raman apontam que para as composições BNBK930 e BNBK912 a simetria predominante em temperatura ambiente é romboédrica (R3c), enquanto que a composição BNBK820 apresenta a simetria cristalina tetragonal (P4mm). Já as composições BNBK879 e BNBK862 apresentaram uma mistura de fases, possivelmente com simetrias romboédrica e tetragonal, evidenciando o contorno de fase morfotrópico (CFM) deste sistema. A microestrutura das cerâmicas de BNBK1000x foi investigada por microscopia eletrônica de varredura (MEV), onde a morfologia apresentada pelas diferentes composições estudadas possuíam grãos com tamanhos e formatos irregulares, sendo que o aumento dos teores dos íons de K+ e Ba2+ inibiram o crescimento dos grãos. A caracterização por espectroscopia Raman, em temperatura ambiente, apresentou modos Raman amplos, mostrando um elevado grau de desordem química e/ou estrutural devido à substituição dos elementos Bi e Na por Ba e K. As caracterizações ferroelétricas, também em temperatura ambiente das cerâmicas de BNBK1000x mostraram que todas as composições estudadas possuem propriedades ferroelétricas. Através da comparação entre as medidas de impedância elétrica e anelástica, levando em consideração as caracterizações estruturais e ferroelétricas com temperatura, foi possível identificar diferentes transições de fase estruturais e elétricas, que foram empregadas na construção de um pseudo-diagrama de fases para as composições de BNBKx.
Sharma, Henu. "Theoretical studies of PbTiO3 and SrTiO3 under uniaxial mechanical constraints combining firstprinciples calculations and phenomenological Landau theory." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENI078.
Повний текст джерелаIn the present thesis we present theoretical studies of perovskite compounds under uniax-ial mechanical constraints combining first-principles DFT calculations approach and phe-nomenological Landau theory. ABO3 perovskites form a very important class of functionalmaterials that can exhibit a broad range of properties (e.g., superconductivity, magnetism,ferroelectricity, multiferroism, metal-insulator transitions. . . ) within small distortions ofthe same simple prototype cubic structure. Though these compounds have been exten-sively studied both experimentally and computationally, there are still unresolved issuesregarding the effect of pressure. In recent years, strain engineering has reported to bean original approach to tune the ferroelectric properties of perovskite ABO3 compounds.While the effect of epitaxial biaxial strain and hydrostatic strain is rather well understoodin this class of materials, very little is yet known regarding the effect of uniaxial mechanicalconstraints. Our study is motivated by the little existing understanding of the effect ofuniaxial strain and stress, that has been up to now almost totally neglected. Two proto-type compounds are studied in detail: PbTiO3 and SrTiO3. After a general introductionon ABO3 compounds and calculations techniques (ab initio and phenomenological Landaumodel), we studied the effect of mechanical constraints in these compounds in our thesis.PbTiO3 is a prototypical ferroelectric compound and also one of the parent components ofthe Pb(Zr,Ti)O3 solid solution (PZT), which is the most widely used piezoelectrics. ForPbTiO3, we have shown that irrespectively of the uniaxial mechanical constraint applied,the system keeps a purely ferroelectric ground-state, with the polarization aligned eitheralong the constraint direction (FEz phase) or along one of the pseudocubic axis perpen-dicular to it (FEx phase). This contrasts with the case of isotropic or biaxial mechanicalconstraints for which novel phases combining ferroelectric and antiferrodistortive motionshave been previously reported. Under uniaxial strain, PbTiO3 switches from a FEx groundstate under compressive strain to FEz ground-state under tensile strain, beyond a critical strain !czz! +1%. Under uniaxial stress, PbTiO3 exhibits either a FEx ground state undercompression ("zz < 0) or a FEz ground state under tension ("zz > 0). Here, however, anabrupt jump of the structural parameters is also predicted under both compressive andtensile stresses at critical values "zz! +2 GPa and −8 GPa. This behavior appears similarto that predicted under negative isotropic pressure and might reveal practically useful toenhance the piezoelectric response in nanodevices.The second compound of interest is SrTiO3. It has been widely studied in the past decadesdue to its unusual properties at low temperature. In this work, we have extended ourprevious investigations on PbTiO3 by exploring theoretically the pressure effects on per-ovskite SrTiO3 combining the first-principles calculations and a phenomenological Landaumodel. We have discussed the evolution of phonon frequencies of SrTiO3 with the threeisotropic, uniaxial and biaxial strains using first-principles calculations. We also reproducethe previous work done in SrTiO3 with epitaxial strain and hydrostatic strain. Finally,we have calculated the phase diagram of SrTiO3 under uniaxial strain, as obtained fromLandau theory and discussed how it compares with the first-principles calculations
Wang, Yanhui. "Hybridization of lamellar oxides : from insertion to in situ synthesis." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAE037/document.
Повний текст джерелаDuring this PhD thesis, we have developed the use of microwave activation to functionalize layered perovskites, among which the Aurivillius phase Bi2SrTa2O9 (BST), known for its ferroelectric properties. We managed to protonate this phase (leading to HST) and to functionalize it by various amines and polyamines, with reaction times much shorter than using classical conditions. This approach allowed us to functionalize HST by bulkier and more complex amines. This strategy has further been extended to the grafting of alcohols and polyols. We have also established a postsynthesis modification strategy, in order to synthesize the desired molecule in situ, within the interlamellar space, using "click" chemistry and microwave activation. Finally, we managed to insert transition metal ions and complexes, which constitutes a promising step towards the synthesis of new multiferroic hybrid materials
Kauffmann, Matthieu. "Structure, dimensionnalité et magnétisme de nouvelles halogéno-cobaltites." Phd thesis, Université des Sciences et Technologie de Lille - Lille I, 2007. http://tel.archives-ouvertes.fr/tel-00198765.
Повний текст джерелаYing-TsuenLin and 林英村. "Synthesis of Inorganic Perovskite Quantum Dots, Characteristic Analysis of Phase Transition and Fabrication of WLEDs:Lighting with High CRI and Display with Wide Color Gamut." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/9suxzc.
Повний текст джерелаYadav, Ruchika. "Growth and Studies of Phase Transitions in Multifunctional Perovskite Materials." Thesis, 2015. http://etd.iisc.ernet.in/2005/3680.
Повний текст джерелаEgilmez, Mehmet. "Magnetotransport and magnetoresistive anisotropy in perovskite manganites." Phd thesis, 2009. http://hdl.handle.net/10048/421.
Повний текст джерелаTitle from pdf file main screen (viewed on July 13, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy, Department of Physics, University of Alberta." Includes bibliographical references.
Munawar, Iram. "Structural and magnetic phase transitions in hexagonal perovskites /." 2004.
Знайти повний текст джерелаMandal, Tapas Kumar. "Perovskite Related Oxides: Development Of New Synthetic Methods, Materials And Properties." Thesis, 2004. http://hdl.handle.net/2005/310.
Повний текст джерелаMani, Rohini. "Investigation Of Transition Metal Oxides Of Perovskite, Pyrochlore And Rutile Structures Towards Realization Of Novel Materials." Thesis, 2009. http://hdl.handle.net/2005/1023.
Повний текст джерелаHan, Qiang. "Electronic and Lattice Contributions to Phase Transitions in Ruthenate Perovskites and Related Compounds." Thesis, 2019. https://doi.org/10.7916/d8-11f6-em72.
Повний текст джерелаMaier, Bernd Jens [Verfasser]. "Phase transitions in advanced relaxor-ferroelectric materials with a perovskite-type structure / vorgelegt von Bernd Jens Maier." 2010. http://d-nb.info/1003355994/34.
Повний текст джерелаSchmidt, Marek Wojciech. "Phase formation and structural transformation of strontium ferrite SrFeOx." Phd thesis, 2001. http://hdl.handle.net/1885/48187.
Повний текст джерелаShet, Tukaram. "Investigations into the Microstructure Dependent Dielectric, Piezoelectric, Ferroelectric and Non-linear Optical Properties of Sr2Bi4Ti5O18 Ceramics." Thesis, 2017. http://hdl.handle.net/2005/3269.
Повний текст джерелаMehner, Erik. "Pyroelektrische Materialien: elektrisch induzierte Phasenumwandlungen, thermisch stimulierte Radikalerzeugung." Doctoral thesis, 2017. https://tubaf.qucosa.de/id/qucosa%3A31917.
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