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1

Bouhajib, Abderrahim. "Étude thermodynamique des systèmes bismuth-calcium et calcium-antimoine : calorimétrie, analyse thermique et modélisation numérique des diagrammes de phases." Nancy 1, 1990. http://www.theses.fr/1990NAN10204.

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Les enthalpies de formation des alliages liquides et d'un certain nombre de composés intermétalliques des systèmes binaires (CA,SB) et (BI,CA) ont été mesurées par calorimétrie Calvet. La méthode convient aussi bien pour la formation des alliages liquides que pour la précipitation progressive de composés solides, par ajouts successifs d'un des constituants. Une étude d'analyse thermique différentielle détaillée a été menée pour le système (CA,SB) ; cette étude a révélé l'existence des nouveaux paliers invariants et des phases nouvelles. Les résultats expérimentaux obtenus pour le système (CA,BI) et CA,SB) ont été confrontés aux diagrammes de phases, à l'aide des programmes de calcul d'harmonisation des données expérimentales (programmes LUKAS et NANCYUN). Les difficultés expérimentales d'élaboration ou de contrôle sont liées à l'oxydabilité du calcium ou de certains de ses alliages, ainsi, la plupart des structures ne peuvent être caractérisées qu'en atmosphère neutre ; certaines synthèses demandent un mode opératoire strict. Les intéractions calcium et métal V-B conduisent à des composés solides stabilisés par une basse enthalpie de formation. On retrouve une enthalpie de mélange très négative en phase liquide. L'invariance de l'enthalpie partielle du calcium dans un large domaine de concentration suggère l'existence d'associations fortes à l'état liquide. Enfin, l'enthalpie de formation de CA#1#1SB#1#0 est plus exoénergétique que celle de CA#1#1BI#1#0, ce qui donne une indication sur la stabilité respective de ces deux phases dans les alliages ternaires
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2

MARTINELLI, ANTONIO E. "Efeito da adicao de chumbo na formacao de fases supercondutoras em ceramicas de Bi-Sr-Ca-Cu-O." reponame:Repositório Institucional do IPEN, 1991. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10260.

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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3

Kim, Seong-Jin. "Directional crystallization in the bismuth-strontium-calcium-copper-oxygen system: Effect of phase separation." Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/186040.

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Novel unidirectional crystallization was tested in glasses of the Bi-Sr-Ca-Cu-O system to produce highly oriented microstructures. Some evidence of liquid-liquid phase separations on cooling melts of Bi₂Sr₂Ca₁Cu₂Oₓ and Pb₀ͺ₃₂Bi₁ͺ₆₈Sr₁ͺ₇₅Ca₂Cu₃Oₓ is found for the first time from Differential Thermal Analysis (DTA), X-ray Diffraction (XRD), and Transmission Electron Microscope (TEM). This made it difficult to produce highly oriented microstructures through the present route because one of the phases in the phase separated structure is likely close to "R"-phase composition and lead to copious nucleation of "R"-phase on heating. This also resulted in sequential crystallization of the current liquids, first to "R"-phase and then to the Bi₂Sr₂Ca₁Cu₂Oₓ phase. Theoretical modelling was performed to understand general questions in the present route. The model suggests that a liquid with high interfacial energy is a good candidate for the present route to produce highly oriented microstructures. The model was tested in lithium diborate glass and showed a highly oriented microstructure. Thus, unidirectional crystallization is generally an attractive processing option for a liquid free of phase separation.
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4

Wan, Xuewen. "Effects of longitudinal disorder on the magnetic field distribution in bismuth strontium calcium copper oxide." W&M ScholarWorks, 2002. https://scholarworks.wm.edu/etd/1539623413.

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Transverse Field muon spin relaxation (TF-muSR) experiments were performed in external magnetic fields 1.0, 2.7, 3.0, 4.5, 5.5, 6.0 and 7.0 T along the Bi2212 crystalline c-axis. For the first time, the heterodyned fitting analysis technique shows that the field profiles on the ab basal planes of single crystal Bi2212 are symmetric in all experimental fields 1.0--7.0 T and at all experimental temperatures 2.0-90.0 K. The muon spin relaxation rates due to the mixed state of Bi2212 were found to increase linearly from 0 mus-1 at the transition temperature, 90.0 K, to about 1.0 mus -1 at the lowest temperature, 2.0 K. The relaxation rates have much less field dependence than the temperature dependence and the field dependence of the relaxation rate is of opposite sign to that seen for YBCO, which is undoubtedly due to vortex lattice disorder caused by the weak coupling between the CuO planes. The scaled magnetic field penetration depths ll0 were found to be independent of magnetic field B in the temperature range 0--50.0 K. Fitting ll0 by currently available models was attempted. A proposed pancake vortex disorder model strongly suggests pancake disordering at all temperatures including 2.0 K, the lowest temperature reached in our experiment. Our experiments and the computer simulation from the pancake vortex disorder model showed that muSR data in this temperature and field range are attributed to the 2-D anisotropic vortex characteristics of Bi2212.
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5

Kim, Cheol Jin. "Laser float zone growth of superconducting bismuth strontium calcium copper oxide fibers: Characterization and phase equilibria." Case Western Reserve University School of Graduate Studies / OhioLINK, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=case1059411650.

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6

Bania, William Roger 1964. "Spray pyrolysis processing of yttrium-barium-copper-oxide and bismuth-strontium-calcium-copper-oxide superconducting thin films." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277080.

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The purpose of this investigation was to explore the processing parameters involved in the production of thin film superconductors by spray pyrolysis processing (SPP). The present study is an attempt to optimize the many parameters in SPP. The specific parameters studied were substrate temperature, carrier gas flow rate, substrate materials, solution stoichiometry, spray rate, concentration, starting materials, and substrate to nozzle distance. The effect of these parameters on film stoichiometry and the anticipated superconducting behavior were investigated at some length. Films were routinely produced in a spray chamber designed as a part of this research. Films were analyzed by Rutherford Backscattering Spectroscopy, X-Ray Diffraction, Scanning Electron Microscopy, and Meissner effect measurements.
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7

Milliken, Damion Alexander. "Uranium doping of silver sheathed bismuth-strontium-calcium-copper-oxide superconducting tapes for increased critical current density through enhanced flux pinning." Access electronically, 2004. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20040810.154223/index.html.

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8

Bouirden, Lahcen. "Transformations continues et discontinues dans les alliages de plomb microalliés au calcium et au calcium étain pour batteries d'accumulateurs : influence de la vitesse de refroidissement : rôle des impuretés argent, aluminium et bismuth." Nancy 1, 1990. http://www.theses.fr/1990NAN10205.

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Les différents processus de vieillissement des alliages PBCA et PBCASN sont observés par des techniques complémentaires telles que la microcalorimétrie anisotherme, la microscopie optique et électronique, la mesure et l'évolution de la dureté en fonction du temps et de la température. Trois états sont étudiés : produit brut de coulée, produit réhomogénéisé et trempé à l'eau, produit réhomogénéisé et refroidi à l'air. Dans les alliages binaires PBCA, nous trouvons trois transformations discontinues successives dans le temps : une première transformation discontinue à front régulier qui est complète et dont la vitesse est constante. Une seconde transformation discontinue complète ou incomplète dont le front est irrégulier et provoque l'aspect puzzle. Ces deux transformations se font sans précipitation observable. Une troisième transformation discontinue, toujours incomplète, provoque la précipitation discontinue lamellaire de PB#3CA au voisinage des joints de grains. Le rôle des impuretés majeures du plomb secondaire est complexe : AG réduit la vitesse des réactions discontinues, BI l'accélère. AL ajoute comme anti-oxydant, affine la taille des grains et accélère ainsi le vieillissement. Les alliages (PB, CA, SN) sont caractérisés par le rapport atomique R=SN/CA. Pour les faibles valeurs de (R=0,7) les processus de vieillissement sont similaires à ceux des alliages PB, CA. Pour les fortes valeurs de R (R3) une précipitation continue généralisée de CASN#3 se manifeste après une période d'incubation. Pour les valeurs de R intermédiaires, les deux processus apparaissent séparément dans le temps. AG accroît la vitesse de germination et réduit le temps d'incubation, BI et AL aussi, mais moins nettement. Les lois cinétiques des différentes transformations sont établies et les énergies d'activation de la première et de la troisième transformation discontinue
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9

Antunes, Laurent. "Caractérisation de composites supraconducteurs aléatoires - phases au bismuth/argent : contribution à l'étude des jonctions faibles dans ces matériaux." Phd thesis, Université Sciences et Technologies - Bordeaux I, 1998. http://tel.archives-ouvertes.fr/tel-00163366.

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Les oxydes supraconducteurs à température critique élevée, à base de bismuth et comportant 2 ou 3 plans cuivre, sont synthétisés suivant diverses méthodes. Nous réalisons ensuite l'élaboration par frittage de matériaux composites aléatoires, constitués d'une dispersion de grains supraconducteurs de phase au bismuth 2212 dans une matrice d'argent. Nous étudions la résistivité électrique et l' aimantation en effet d'écran des matériaux en fonction de la température, du champ magnétique et de la concentration en phase supraconductrice. Les comportements observés sont interprêtés dans le cadre d'une approche phénoménologique impliquant la notion de "liens supraconducteurs faibles". Enfin, nous tentons de relier, par des mesures de spectroscopie de photoelectrons X, les informations statistiques obtenues aux caractéristiques chimiques des jonctions intergranulaires.
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10

Rowan, Fraser S. "A study of the effects of oxygen environment on the stoichiometry, phase assemblage and stability of BiSCCO 2212 and 2201 using EPMA." Thesis, University of Aberdeen, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369139.

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A method of performing accurate oxygen analysis on cuprate based superconducting materials was established using electron probe micro analysis (EPMA). A range of YBa2Cu3Oδ ceramics with varying oxygen concentration were used to test the method. Using YBCO as a reference material, a suitable standard for oxygen analysis of Bi2Sr2CaCu2Oδ (BiSCCO-2212) materials was obtained. This standard was used to perform full elemental analysis of a range of BiSCCO-2212 crystals, post annealed in pO2's between 10-5-2atm. When the average Cu valence of each crystal was calculated and plotted as a function of the critical temperature (Tc) for each crystal, it was shown that BiSCCO-2212 materials conformed to the 'universal' trend illustrated by most other HTS and did not exhibit anomalous behaviour as had been previously believed. The phase assemblage and superconducting properties of BiSCCO-2212 Ag-clad multifilamental wires, prepared using the powder-in-tube (PIT) method by BICC, were studied as a function of a time/temperature profile. pO2 of the processing atmosphere was found to be the predominant factor in determining the stoichiometry of the 2212 phase within wires. The phase assemblage is not simply a function of pO2 as previously believed and can be controlled, in part, by the post annealing temperature. Homogenisation of the phase assemblage in BiSCCO-2212 Ag-clad wires can be achieved by prolonged heating (96hrs) at an appropriate temperature. An investigation into the 10K superconducting BiSCCO phase has shown the Sr-rich solid solution to extend towards the ideal stoichiometry of 2:2:1 (Bi:Sr:Cu) with increasing pO2. Using a combination of high pO2 (60atm) to achieve the appropriate Bi:Sr stoichiometry followed by post annealing in N2 to adjust the oxygen content, it was possible to prepare single-phase ceramics of stoichiometry Bi2.11(2)Sr1.90(2)Cu0.99(2)Oδ with a Tc=10.5K(5).
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11

Balmer, B. R. "Processing studies on Bi-2212 superconducting thick films." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326142.

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12

Gay, Pierre. "Ultrafast processes in high temperature superconductors." Thesis, University of Oxford, 2000. https://ora.ox.ac.uk/objects/uuid:140cc366-58a1-41ad-919b-2cb5f65c3fe9.

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Using time-resolved photo-induced reflectivity, we reported for the first time a systematic work on the ultrafast response of Bi2Sr2CaCu2O8+δ (BSCCO-2212) and Tl2Ba2CuO6+δ (TBCO-2201), measurements of detwinned YBa2Cu3O7-δ (YBCO-123) single crystal with the electric field ̲E parallel to the a and b-axis and high-resolution measurements of the rising edge dynamics of YBCO-123 thin films. We identified similar photo-induced responses for BSCCO, TBCO and for YBCO with ̲E ⊥ ̲b, which indicates that we observed a universal response of HTSC coming from the CuO2 superconducting planes. This latter dynamics is composed of three different components corresponding to the superconducting, pseudogap and normal state. A bi-molecular model has been put forward to explain the linear temperature dependence of the decay rate; the model implies that the re-formation of the condensate is limited by the rate at which quasiparticle interact. Moreover, we observed superconducting fluctuations up to 13K above Tc and a divergence of the long-lived component magnitude at very low temperature, which is explained by a cw heating model. In the pseudogap state, we have several indications that the negative peak observed between Tc and T* has a different origin from that of the superconducting signal below Tc. We argued that the probe mechanism of the pseudogap signal is electronic excitations of the pseudogap correlations. In the normal state, the observed dynamics is similar to that of simple metals. In the second part of this thesis, the rising edge dynamics of YBCO has been resolved in time. The model developed to interpret the results implies that the hot quasiparticles relaxation time down to the Fermi energy is 55fs. In this context, we proved that the Mazin model cannot explain both the oscillatory and the non-oscillatory part of the dynamics in YBCO. Finally, in YBCO-123, a new response has been observed with ̲E ∥ ̲b. We argued that the origin of this component is intraband transitions. This dynamics is solely responsive to the pseudogap, coming from the difference in scattering rate between pre-formed pairs and quasiparticles in the Drude reflectivity. The response with ̲E ⊥ ̲b exhibits a strong a-b plane anisotropy in its long-lived component, which can be interpreted as a d-wave gap symmetry using the thermally-activated model.
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13

Richens, P. E. "High temperature superconductors in electromagnetic applications." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365792.

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14

Bolt, Livia. "Magnetic separation using high-T←c superconductors." Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368332.

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15

Saleh, Paul Matthew. "Characterisation of practical high temperature superconductors in pulsed magnetic fields and development of associated technology." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365786.

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16

Lloyd, Sion. "The magnetic properties of superconductors." Thesis, University of Birmingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343847.

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17

Feltham, Stuart Paul. "An investigation of stoichiometetry and thermo-mechanical processing parameters of (Pb,Bi)←2Sr←2Ca←2Cu←3O←x superconducting tapes." Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368331.

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18

Pavard, Sybille. "Texturation de massifs supraconducteurs Bi2Sr2CaCu2O(8+x) avec ajout de MgO." Université Joseph Fourier (Grenoble), 1999. http://www.theses.fr/1999GRE10029.

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Ce travail a ete consacre a la texturation, par solidification sous champ magnetique et forgeage, de massifs supraconducteurs bi2212 avec ajout de mgo dans le but d'obtenir de fortes densites de courant critique jc. La texturation de massifs bi2212, obtenue par orientation preferentielle de l'axe c selon la direction du champ magnetique applique lors de la solidification, a tout d'abord ete demontree par des caracterisations microstructurales et supraconductrices. Ce procede a ete ameliore par ajout de poudre mgo a la poudre initiale : celui-ci apporte une tenue mecanique au materiau a haute temperature. Cet ajout augmente le degre de texturation induit par le champ magnetique, ameliore la connexion entre plaquettes, reduit le taux volumique des phases residuelles, et induit la presence d'inclusions submicroniques riches en mgo au sein de la matrice. Ces observations ont permis d'expliquer la nette amelioration des proprietes supraconductrices obtenues par ajout de mgo, en particulier : une meilleure tenue sous champ magnetique du jc, une augmentation d'un facteur 2. 5 du jc a 77 k, et un doublement des champs d'irreversibilite. Une etude par diffraction des neutrons a montre le fort degre de texture present dans tout le volume des echantillons. L'association du forgeage a la solidification sous champ magnetique des massifs bi2212/mgo ameliore cette texture. L'application d'une contrainte uniaxiale a chaud apres la solidification sous champ a permis d'augmenter le jc et les champs d'irreversibilite des massifs bi2212/mgo textures. Par une etude des recuits sous atmosphere controlee de ces massifs bi2212/mgo textures, un jc superieur a 1900 a/cm#2 a 77 k a ete atteint. L'ajout de mgo et la texturation par solidification sous champ magnetique suivie d'un forgeage ont permis d'obtenir des massifs bi2212 textures dont les jc a basses temperatures atteignent les valeurs observees dans les rubans et les multifilamentaires : 165 ka/cm#2 a 4 k.
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19

AYADI, MOHAMED. "Contribution a l'etude de la dynamique de reseau de quelques composes de la serie de la mathlockite (pbfcl)." Université Louis Pasteur (Strasbourg) (1971-2008), 1986. http://www.theses.fr/1986STR13183.

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Etude de l'energie de cohesion de composes a structure de mathlockite; conditions de stabilite, expressions de la polarisation ionique, des constantes d'elasticite et des constantes dielectriques (modele de la coquille, presence de sites non centrosymetriques). Condition de synthese et de croissance cistalline de cahcl, bafcl, pbfcl et biocl; spectres raman et ir. Analyse des spectres de reflexion ir de bafcl (kramers-kronig et oscillateur classique). Determination de la densite d'etats et de la dispersion de phonons pour bafcl; calcul de certaines constantes d'elasticite
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20

Noudem, Jacques Guillaume. "Texturation des céramiques supraconductrices Bi-Pb-Sr-Ca-Cu-O par combinaison des effets du champ magnétique et de la contrainte uniaxiale à haute température." Université Joseph Fourier (Grenoble), 1995. http://www.theses.fr/1995GRE10169.

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Les ceramiques supraconductrices des composes bi-(pb)-sr-ca-cu-o ont une capacite de transport de courant electrique a 77 k faible qui est due a la presence des porosites et a la desorientation des feuillets. Pour obtenir des densites de courant critique de transport elevees dans ces materiaux, il est necessaire de les densifier et d'induire une orientation cristallographique preferentielle. Un procede permettant de texturer par effet combine du champ magnetique et de la contrainte uniaxiale a haute temperature a ete mis au point. Le dispositif experimental permet d'appliquer une pression uniaxiale de 60 mpa sous un champ magnetique de 8 t jusqu'a une temperature de 1100c. Les echantillons elabores sont obtenus a partir des precurseurs industriels (hoechst) de la phase bi:2223. La technique de texturation par solidification sous champ magnetique s'est averee tres efficace pour obtenir des echantillons massifs polycristallins bi-(pb)-sr-ca-cu-o orientes avec l'axe-c des cristallites parallele au champ magnetique applique. Les densites de courant critiques (jc) obtenues par ce procede sont de 1450 a/cm#2 pour une densite de 5. 1 g/cm#3 (82% de la densite theorique). La texturation par fluage sous contrainte uniaxiale, a permis d'obtenir des ceramiques denses ( 6 g/cm#3), homogenes ayant des densites de courant critiques de 2500 a/cm#2. Les rubans ag/bi:2223 fournis par alcatel alsthom ont aussi ete textures avec succes par le procede de pressage a chaud. La combinaison du champ magnetique et de la contrainte uniaxiale permet d'ameliorer la texture et la densite des echantillons qui par ailleurs sont tres homogenes et possedent une bonne tenue mecanique. Les densites de courant critique de transport a 77 k atteignent 3800 a/cm#2 suivant les plans (a,b) et 1100 a/cm#2 suivant l'axe-c. Par ailleurs, nous avons mis en evidence la possibilite d'utiliser ces ceramiques texturees dans le domaine de l'electrotechnique pour limiter le courant
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21

Azzaoui, Mouhsine. "Modélisation des liquides métalliques ternaires pour le calcul des diagrammes d'équilibre à partir des mesures thermodynamiques ciblées : systèmes tests : (Pb, Sn, Sb), (Pb, Sn, Bi), (Pb, Sn, Ca)." Nancy 1, 1995. http://www.theses.fr/1995NAN10032.

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Le calcul des diagrammes d'équilibre ternaires nécessite une bonne représentation analytique des grandeurs thermodynamiques d'excès des phases étendues. L’établissement de ces fonctions doit s'appuyer sur un nombre minimum, mais suffisant, d'informations expérimentales. Le formalisme quadratique de Darken, dans le cas des systèmes ternaires, permet de lisser les grandeurs d'excès dans les domaines des solutions moyennement diluées (xi 0,333). En divisant un système ternaire en trois quadrilatères adjacents, le formalisme de Darken nécessite 12 paramètres d'interaction binaires et seulement 3 paramètres d'interaction ternaires pour accéder à trois représentations distinctes, mais complémentaires, chacune valable dans l'un des trois quadrilatères. Un nombre très restreint de mesures ternaires est donc requis. Les fonctions d'excès représentées par le formalisme de Darken présentent des discontinuités sur les isoplèthes de raccordement des 3 quadrilatères. Un développement aux 5eme degré des polynômes de Redlich-Kister permet d'accéder à une représentation continue des fonctions d'excès. La validité de nos deux méthodes d'ajustement a été testée avec succès dans le cas des solutions liquides ternaires (Pb, Sn, Sb), (Pb, Sn, Bi) tt (Pb Sn, Ca). Enfin, pour le calcul des diagrammes d'équilibre, qui reste l'objectif final de ce travail, nous avons tenté avec succès une optimisation des paramètres ajustables décrivant les phases binaires et ternaires du système (Pb, Sn, Sb) en utilisant les deux logiciels Thermo-Calc et Nancyun
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22

Timrov, Iurii. "Étude ab initio des plasmons et du couplage électron-phonon dans le bismuth: de la modélisation de l'absorption des porteurs libres à une nouvelle méthode pour le calcul de spectre de perte d'énergie électronique." Phd thesis, Ecole Polytechnique X, 2013. http://pastel.archives-ouvertes.fr/pastel-00823758.

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Ce travail a été consacré à l'étude théorique du bismuth semi-métallique à l'aide de méthodes basées sur la théorie de la fonctionnelle de la densité (DFT). Les effets de couplage spin-orbite et d'échange et de corrélation dans l'approximation de densité locale (LDA) et de gradient généralisé (GGA) ont été approfondis de façon systématique. J'ai trouvé que les poches d'électrons et de trous au niveau de Fermi sont correctement décrites, ce qui m'a permis d'interpréter avec succés les expériences pompe-sonde dans le bismuth photoexcité menées au laboratoire des Solides Irradiés. Le calcul du couplage électron-phonon a montré la forte dépendance, par rapport au vecteur d'onde électronique, du couplage de la bande de valence la plus haute avec le phonon A1g LO de centre de zone, ce qui explique l'observation de la forte dépendance en k de l'amplitude d'oscillation de l'énergie de liaison de cette même bande en photoémission résolue en temps. J'ai aussi montré que la présence d'extréma dans les bandes de valence et de conduction, où la masse des porteurs peut atteindre 18 m0, favorise une accumulation des porteurs et conduit à une augmentation de leur fréquence plasma au cours du temps aprés photoexcitation, un effet qui n'a pas (encore) été observé dans d'autres matériaux. Enfin, j'ai développé une nouvelle méthode en théorie de perturbation de la fonctionnelle de la densité dépendante du temps (TDDFPT), qui permet de calculer la réponse électronique du matériau pour n'importe quelle valeur du moment transféré. Cette approche basée sur la méthode de récursion de Lanczos m'a permis de calculer les spectres de perte d'énergie électronique de Bi dans la gamme d'énergie 0-100 eV et de combler l'intervalle d'énergie entre les pertes des électrons de valence et celles des électrons de cœur. Cette méthode ouvre des perspectives considérables, comme le calcul des plasmons de surface.
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23

温國宏. "Films Thickness Dependence of Ferroelectric and Photovoltaic Properties of Calcium Doped Bismuth Ferrite." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/47260632657294266642.

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碩士
國立新竹教育大學
應用科學系碩士班
103
In this experiment, the photovoltaic effect with different film thickness of 5% Ca doped BiFeO3 thin films were investigated. The probable physical mechanism were carried out many different measurements which may affect the efficiency of the photovoltaic effect. The specimen of BFO thin films and the electrode were all deposited on Si(100) by RF magnetron sputtering. First, we grew LaNiO3 on Si(100) at 450 . Second, The 5% Ca doped BiFeO3 films were deposited on LaNiO3. Third, we deposited Pt or AZO to do measurements, respectively. Film thickness was estimated by SEM and X-ray reflectivity. Film crystallinity was carried out by X-ray diffraction measurement. The morphology was measured by atomic force microscope and X-ray reflectivity. The hysteresis loop was performed by TF-2000 and the photovoltaic effect were measured by 405 nm laser. BFO was (100) highly preferred along Si (100) substrate from X-ray diffraction measurement. BFO film strain relax as film thickness increase, hence the diffraction peak position shift more close to the expected bulk value. The surface roughness, which was carried out by AFM and X-ray reflectivity has little increase as film thickness thicker. The hysteresis loop showed that the polarization slow down as the film thickness increased. The photovoltaic effect also slow down as the film thicker. The BFO built-in electric field affect the efficiency of photovoltaic effect. As the film thickness increased to 100 nm, the strain relax caused built-in electric field become weaker and the probability of electron and hole recombined increase due to distance between two electrode; therefore, the efficiency of photovoltaic hidden.
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24

Cai, Ren-Fong, and 蔡任豐. "Preparation and Photocatalytic Activity Study of Calcium Bismuth Oxide Photocatalysts with Core-shell Structure." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/bp52c7.

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碩士
國立東華大學
材料科學與工程學系
95
Core-shell structure calcium bismuth oxide photocatalysts prepared by chemical impregnation method. The result indicated adding HNO3 can promoted the reaction. From the different reaction temperature experiments, we found that in the 500℃and 550℃have the best photocatalysic activities. Reacted in the 550℃,generated special band structure due to the core-shell structure. It makes the electron-hole pairs separated well. From the different reaction temperature and time experiments, when the reaction temperature in the 450℃, a lot of Bi5O7NO3 were formed, and it decomposed during the second reaction. Temperature is the main factor of the calcium bismuth oxide phase formation. In the same reaction temperature, its phase are the same, and the phase ratio are slight different. The Ca/Bi ratio is the important factor during the reaction. The higher Ca/Bi ratio, the better photocatalytic activities are observation, and the reacted in the 500℃ photocatalysts photocatalytic activities are better than reacted in the 450℃.
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25

Cho, Jae-Ik. "The influence of trace element effects of calcium, phosphorus and bismuth in aluminum casting alloys." 1999. http://catalog.hathitrust.org/api/volumes/oclc/44538989.html.

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26

Pires, Tatiana Rafaela Lopes. "Comparative analysis of chromatic alterations of a Calcium Silicate-based Material: in vitro study." Master's thesis, 2014. http://hdl.handle.net/10316/36720.

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Trabalho final do 5º ano com vista à atribuição do grau de mestre no âmbito do ciclo de estudos de Mestrado Integrado em Medicina Dentária apresentado à Faculdade de Medicina da Universidade de Coimbra.
Objective: The purpose of this study was to investigate and compare chromatic alterations of an inorganic silicate-based cement, also known as white mineral trioxide aggregate (WMTA), submitted to different environmental conditions using the CIE L*a*b* system evaluated by two different methods. Methods: Twenty-four samples of WMTA (ProRoot® MTA, Dentsply Tulsa Dental, Johnson City, TN) were randomly distributed in four groups (n=4). In group 1 the samples did not undergo any additional treatment (negative control group). In group 2 WMTA samples were light irradiated for 60 seconds using a LED poliwave curing unit. In group 3 and 4 WMTA samples were coated with a layer of glycerine and adhesive, respectively and light irradiated for 60 seconds. A commercial spectrophotometer (VITA Easyshade® Advance 4.0, VidentTM, California, USA) and calibrated photographic digital analysis were used to determine colour coordinates from the CIE L*a*b* system of each sample after three different time points: 30 minutes, 48 hours and 7 days. In order to understand the chemical alterations associated to colour variations of the material x-ray diffraction analysis was also conducted. Data was analysed using statistical software IBM® SPSS® Statistics, version 20. Results: Consistency between the two colour measuring methods was not observed. Significant colour variation was observed for group 3. X-ray diffraction analysis showed no differences between compounds. Conclusion: WMTA showed significant dark discolouration after irradiation with an LED poliwave curing unit in an oxygen-free environment promoted by glycerine although after 48 hours discolouration had faded. The same light irradiation protocol associated to an oxygen-free conditions achieved by an adhesive resin layer did not induce significant discolouration at the end of the experiment protocol.
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27

Wang-JenLi and 李婉甄. "The effects of calcium and other element substitution on the electric and photoelectric properties of bismuth ferrite." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/41204950239370020978.

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Abstract:
碩士
國立成功大學
材料科學及工程學系碩博士班
101
The aim of this study was to search for ferroelectric photovoltaic materials. In contrast to the semiconductor p-n junction, where the photovoltaic voltage is limited to around 0.6 V, the spontaneous polarization in ferroelectric materials can produce a much higher output voltage. Indeed, in a recent work, a large photovoltaic output of over 20 V has been demonstrated with the BiFeO3 single crystals. However, because ferroelectric materials usually have a very high DC resistivity over 108 ohm-cm, there is a need to increase the mobile carrier concentration in these materials. For this purpose, BiFeO3 (BFO) was doped with various ions in the present study. Polycrystalline pellets of BFO:M (M=Ca, Pb, Sr and Ni) were prepared by the sol-gel method. After poling, the photoelectric effects of the samples were studied. X-ray diffraction showed that after sintering at 500~600oC for 12 hours, undoped BFO and the samples doped with Ca, Pb, Sr and Ni had a pure phase with the well-known rhombohedral structure. If the sintering temperature was raised to 700oC, a second phase of the composition Bi25FeO40 appeared. The resistivities of the BFO samples doped with Ca, Pb, Sr, and Ni doped were measured to be 106~107 ohm-cm, which were1~2 orders lower than that of the undoped BFO. The samples were poled under a high electrical field at 600oC. The degree of the achieved poling was checked by the measured d33 values. I-V curves and photovoltaic effects of the samples with a large d33 were then investigated. The experiment results showed that under suitable preparation conditions (e.g. sintering temperature and time, degree of achieved poling, etc.), an open-circuit voltage was usually observed in the samples. After the samples were illuminated by the simulated-sunlight, large current increases were observed in the I-V curves. The undoped BFO showed a largest negative open-circuit voltage of -1.25 V, whereas the open-circuit voltages for Ca and Ni doped BFO were -0.75 and -0.2 (V), respectively. On the other hand, The Ca and Ni doped samples showed the largest photocurrents, which were increased from 10-9 A at dark to 10-8 A after the illumination. The undoped BFO showed a trivial photocurrent after illumination, indicating a lack of mobile charge carrier which could be excited by the light.
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28

Garg, Rohini. "Structural, Ferroelectric, Piezoelectric and Phase Transition Studies of Lead Free (Na0.5Bi0.5)TiO3 Based Ceramics." Thesis, 2013. http://etd.iisc.ac.in/handle/2005/3446.

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Abstract:
Ferroelectric materials, especially the polycrystalline ceramics, are very promising material for a variety of applications such as high permittivity dielectrics, ferroelectric memories, piezoelectric sensors, piezoelectric/electrostrictive transducers, electrooptic devices and PTC thermistors. Among the ferroelectric based piezoelectric ceramics the lead–zirconate-titanate Pb(Zr1-xTix)O3 (PZT) have dominated transducer and actuator market due to its excellent piezoelectric and dielectric properties, high electromechanical coupling, large piezoelectric anisotropy, ease of processing and low cost. However, the toxicity of lead based compounds has raised serious environmental concerns and therefore has compelled the researchers to look for new lead free alternatives with good piezoelectric and ferroelectric properties. (Na0.5Bi0.5)TiO3 (NBT) and its solid solution is one of the leading lead free piezoceramic ceramics due to their interesting ferroelectric, piezoelectric, electromechanical and dielectric property. The parent compound NBT is a ferroelectric with a moderately high Curie temperature (~250 oC), large ferroelectric polarization (~40µC/cm2) polarization, promising piezoelectric properties with 0.08% strain and longitudinal piezoelectric coefficient (d33) ~ 80 pC/N. X-ray and neutron diffraction studies in the past have shown that NBT exhibits rhombohedral (R3c) at room temperature. Neutron diffraction studies have suggested that NBT undergo a gradual rhombohedral to tetragonal (P4bm) transformation in a temperature region 200-320 ºC. Though the structure and phase transition behavior of NBT has been extensively investigated for over six decades now, this subject has again become debatable in recent few years, with some group reporting formation of orthorhombic phase above room temperature and another group suggesting monoclinic distortion at room temperature using high resolution x-ray diffraction technique. Interestingly the intermediate orthorhombic instability, reported by electron diffraction studies, has never been captured by neutron diffraction method though neutron diffraction is an equally powerful tool for studying (oxygen) octahedral tilts in perovskites. Needless to mention, the understanding of the subtle structural distortions have great significance with regard to the determination of the structure-piezoelectric property correlations in NBT based piezoceramics. The present thesis deals with such subtle structural issues in great detail. The systems investigated in the thesis are Ca and Ba modified NBT. While the Ca modified system was chosen to understand the subtle orthorhombic instability that has been reported above room temperature (only) by detailed electron diffraction work, Ba-modified NBT is the most investigated among the NBT-derived piezoelectric material systems and this thesis attempts to address some of the very complex nature of the structure-piezoelectric property correlation of this system. The first chapter of the thesis provides a brief introduction to the field of ferroelectrics, perovskite structure and their phase transition. A brief exposure to the conventional lead based relaxor ferroelectric and piezoelectric material is provided. A detailed overview of the existing knowledge related to room temperature structure of NBT and its phase transition studies with temperature has been discussed in the later part of this chapter. The second chapter includes various the experimental techniques that have been employed to synthesis and characterize the specimens under investigation. The third chapter deals with the phase transition behaviour of Ca modified NBT as a function of composition and temperature in the dilute concentration region. This work was carried out with the view to obtain a better understanding and compliment the intrinsic high temperature orthorhombic instability in NBT reported by electron diffraction technique. Interestingly, inspite of the fact that neutron diffraction method is a very sensitive tool for investigating subtle change in the nature of octahedral tilt in oxide perovskites, the intermediate orthorhombic distortion proposed by the electron diffraction studies has so far never been captured in any of the neutron diffraction studies. In this work we have verified the genuineness of the intrinsic instability with regard to the non-polar orthorhombic structure using neutron powder diffraction by adopting a special strategy which helped in capturing the characteristic signatures (the superlattice reflections) of the orthorhombic phase in the neutron powder diffraction patterns. It was found that small fraction of Ca-substitution (8-10 mol %) was good enough to amplify the magnitude of the orthorhombic (Pbnm) distortion, without altering the sequence of the structural evolution with temperature of the parent compound (NBT) itself, and stabilizing it at the global length scale at lower temperatures than pure NBT. This chapter presents the innovative approach that was used to extract reliable information about the very complex phase transition behaviour, involving coexistence of the various similar looking but crystallographically different phases in different temperature regimes by Rietveld analysis of temperature dependent neutron powder diffraction pattern in conjunction with temperature dependent dielectric and ferroelectric characterization of the specimens. The detailed study revealed the following sequence of structural evolution with temperature: Cc+Pbnm →Pbnm + P4/mbm → P4/mbm →Pm3 m. The fourth chapter gives a detail account of the structure-property correlations and the phase transition behaviour of (1-x)(Na0.5Bi0.5)TiO3 – (x)BaTiO3 (0≤x≤0.10), the most important solid solution series with NBT as reported in the literature. The phase transformation behaviour of this system has been investigated as a function of composition (0
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29

Garg, Rohini. "Structural, Ferroelectric, Piezoelectric and Phase Transition Studies of Lead Free (Na0.5Bi0.5)TiO3 Based Ceramics." Thesis, 2013. http://etd.iisc.ernet.in/2005/3446.

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Abstract:
Ferroelectric materials, especially the polycrystalline ceramics, are very promising material for a variety of applications such as high permittivity dielectrics, ferroelectric memories, piezoelectric sensors, piezoelectric/electrostrictive transducers, electrooptic devices and PTC thermistors. Among the ferroelectric based piezoelectric ceramics the lead–zirconate-titanate Pb(Zr1-xTix)O3 (PZT) have dominated transducer and actuator market due to its excellent piezoelectric and dielectric properties, high electromechanical coupling, large piezoelectric anisotropy, ease of processing and low cost. However, the toxicity of lead based compounds has raised serious environmental concerns and therefore has compelled the researchers to look for new lead free alternatives with good piezoelectric and ferroelectric properties. (Na0.5Bi0.5)TiO3 (NBT) and its solid solution is one of the leading lead free piezoceramic ceramics due to their interesting ferroelectric, piezoelectric, electromechanical and dielectric property. The parent compound NBT is a ferroelectric with a moderately high Curie temperature (~250 oC), large ferroelectric polarization (~40µC/cm2) polarization, promising piezoelectric properties with 0.08% strain and longitudinal piezoelectric coefficient (d33) ~ 80 pC/N. X-ray and neutron diffraction studies in the past have shown that NBT exhibits rhombohedral (R3c) at room temperature. Neutron diffraction studies have suggested that NBT undergo a gradual rhombohedral to tetragonal (P4bm) transformation in a temperature region 200-320 ºC. Though the structure and phase transition behavior of NBT has been extensively investigated for over six decades now, this subject has again become debatable in recent few years, with some group reporting formation of orthorhombic phase above room temperature and another group suggesting monoclinic distortion at room temperature using high resolution x-ray diffraction technique. Interestingly the intermediate orthorhombic instability, reported by electron diffraction studies, has never been captured by neutron diffraction method though neutron diffraction is an equally powerful tool for studying (oxygen) octahedral tilts in perovskites. Needless to mention, the understanding of the subtle structural distortions have great significance with regard to the determination of the structure-piezoelectric property correlations in NBT based piezoceramics. The present thesis deals with such subtle structural issues in great detail. The systems investigated in the thesis are Ca and Ba modified NBT. While the Ca modified system was chosen to understand the subtle orthorhombic instability that has been reported above room temperature (only) by detailed electron diffraction work, Ba-modified NBT is the most investigated among the NBT-derived piezoelectric material systems and this thesis attempts to address some of the very complex nature of the structure-piezoelectric property correlation of this system. The first chapter of the thesis provides a brief introduction to the field of ferroelectrics, perovskite structure and their phase transition. A brief exposure to the conventional lead based relaxor ferroelectric and piezoelectric material is provided. A detailed overview of the existing knowledge related to room temperature structure of NBT and its phase transition studies with temperature has been discussed in the later part of this chapter. The second chapter includes various the experimental techniques that have been employed to synthesis and characterize the specimens under investigation. The third chapter deals with the phase transition behaviour of Ca modified NBT as a function of composition and temperature in the dilute concentration region. This work was carried out with the view to obtain a better understanding and compliment the intrinsic high temperature orthorhombic instability in NBT reported by electron diffraction technique. Interestingly, inspite of the fact that neutron diffraction method is a very sensitive tool for investigating subtle change in the nature of octahedral tilt in oxide perovskites, the intermediate orthorhombic distortion proposed by the electron diffraction studies has so far never been captured in any of the neutron diffraction studies. In this work we have verified the genuineness of the intrinsic instability with regard to the non-polar orthorhombic structure using neutron powder diffraction by adopting a special strategy which helped in capturing the characteristic signatures (the superlattice reflections) of the orthorhombic phase in the neutron powder diffraction patterns. It was found that small fraction of Ca-substitution (8-10 mol %) was good enough to amplify the magnitude of the orthorhombic (Pbnm) distortion, without altering the sequence of the structural evolution with temperature of the parent compound (NBT) itself, and stabilizing it at the global length scale at lower temperatures than pure NBT. This chapter presents the innovative approach that was used to extract reliable information about the very complex phase transition behaviour, involving coexistence of the various similar looking but crystallographically different phases in different temperature regimes by Rietveld analysis of temperature dependent neutron powder diffraction pattern in conjunction with temperature dependent dielectric and ferroelectric characterization of the specimens. The detailed study revealed the following sequence of structural evolution with temperature: Cc+Pbnm →Pbnm + P4/mbm → P4/mbm →Pm3 m. The fourth chapter gives a detail account of the structure-property correlations and the phase transition behaviour of (1-x)(Na0.5Bi0.5)TiO3 – (x)BaTiO3 (0≤x≤0.10), the most important solid solution series with NBT as reported in the literature. The phase transformation behaviour of this system has been investigated as a function of composition (0
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30

Shet, Tukaram. "Investigations into the Microstructure Dependent Dielectric, Piezoelectric, Ferroelectric and Non-linear Optical Properties of Sr2Bi4Ti5O18 Ceramics." Thesis, 2017. http://etd.iisc.ac.in/handle/2005/3269.

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Abstract:
Ferroelectric materials are very promising for a variety of applications such as high-permittivity capacitors, ferroelectric memories, pyroelctric sensors, piezoelectric and electrostrictive transducers and electro-optic devices, etc. In the area of ferroelectric ceramics, lead-based compounds, which include lead zirconatetitanate (PZT) solid solutions, occupy an important place because of their superior physical properties. However, due to the toxicity of lead, there is an increasing concern over recycling and disposing of the devices made out of these compounds, which has compelled the researchers around the globe to search for lead-free compounds with promising piezo and ferroelectric properties. Ferroelectric materials that belong to Aurivillius family of oxides have become increasingly important from the perspective of industrial applications because of their high Curie-temperatures, high resistivity, superior polarization fatigue resistanceand stable piezoelectric properties at high temperatures. These bismuth layer-structured ferroelectrics (BLSF) comprise an intergrowth of [Bi2O2]2+ layers and [An+1Bn O3n+1]2- pseudo-perovskite units, where ‘n’ represents the number of perovskite-like layers stacked along the c-axis. ‘A’ stands for a mono-, di- or trivalent ions or a combination of them, ‘B’ represents a small ion with high valencysuch as Ti4+, Nb5+, Ta5+or a combination of them.Ferroelectricity in the orthorhombic phase of these compounds was generally attributed to the cationic displacement along the polar a-axis and the tilting of octahedra around the a- and c-axes. Sr2Bi4Ti5O18(SBT) is ann = 5 member of the Aurivillius family and possess promising ferroelectric and piezoelectric properties that could be exploited for a wide range of applications, including ferroelectric random access memories (FeRAM), piezoelectric actuators, transducers and transformers. Reports in the literaturereveal that the ferroelectricand piezoelectric properties of these oxides can be tuned depending on synthesis routes vis-a-vis micro-structural aspects (texture, grain size) and site specific dopant substitutions.In the present study, textured SBT ceramics were fabricated using pre-reacted precursors and their anisotropic dielectric, piezoelectric and ferroelectric properties were demonstrated. Grain size tunability with regard to their physical properties was accomplished in the ceramics, fabricated using fine powders obtained from citrate assisted sol-gel synthesis. The grain size dependent second harmonic generation activity of SBT ceramics was investigated. Enhancement in the piezoelectric and ferroelectric properties of SBT ceramics was achieved by substituting A site ions (Sr2+) with a combination of Na+ and Bi3+. From the perspective of non-linear optical device applications, physical properties associated with the SBT crystallized in a transparent lithium borate glass matrix were studied. The results obtained in the present investigations are organized as follows, Chapter 1 gives a brief exposure to the field of ferroelectrics. The emphasis has been on the ferroelectric oxides belonging to the Aurivillius family. Structural aspects and the underlying phenomena associated with ferroelectricity in these compounds are discussed. A brief introduction to the glasses, thermodynamic aspects of glass formation and fabrication of glass- ceramics are included. Basic principles involved in the non-linear optical activities are highlighted. Chapter 2 describes the various experimental techniques that were employed to synthesize and characterize the materials under investigation. The experimental details pertaining to the measurement of various physical properties are included. Chapter 3 deals with the fabrication of Sr2Bi4Ti5O18 ceramics using the pre-reacted Bi4Ti3O12 and SrTiO3 powders viasolid-state reaction route. These in stoichiometric ratio were uniaxially pressed and sintered at 1130oC for 3 h resulting in textured Sr2Bi4Ti5O18 ceramics. The obtained dense ceramics exhibited crystallographic anisotropy with prominent c-axis oriented grains (Lotgering factor of 0.62) parallel to the uniaxially pressed direction. The resultant anisotropy in the ceramics was attributed to the reactive template-like behavior of Bi4Ti3O12 that was used as a precursor to fabricate Sr2Bi4Ti5O18 ceramics. Dielectric, ferro and piezoelectric properties measured on the ceramics in the direction perpendicular to the uniaxially pressed axis were found to be superior to that measured in the parallel direction. Chapter 4 reports the details pertaining to the synthesis of strontium bismuth titanate (Sr2Bi4Ti5O18) powders comprising crystallites of average sizes in the range of 94–1400 nm via citrate-assisted sol-gel route. X-ray powder diffraction, Transmission Electron Microscopy (TEM) and Raman spectroscopy were employed for the structural studies. A crystallite size-dependent variation in the lattice parameters and the shift in the Raman vibration modes were observed. Second harmonic signal (532 nm) intensity of the Sr2Bi4Ti5O18 powders increased with the increase in the average crystallite size and the maximum intensity obtained in the reflection mode was 1.4 times as high as that of the powdered KH2PO4. Piezo force microscopic analyses carried out on an isolated crystallite of size 74 nm, established its single domain nature with the coercive field as high as 347 kV/cm. There was a systematic increase in the d33 value with an increase in the size of the crystallite and a high piezoelectric coefficient of ~27 pm/V was obtained from an isolated crystallite of size 480 nm. Chapter 5 illustrates the details concerning the fabrication of Sr2Bi4Ti5O18(SBT) ceramics with different grain sizes (93 nm–1.42 μm) using nano-crystalline powders synthesized via citrate assisted sol-gel method. The grain growth in these powder compacts was found to be controlled via the grain boundary curvature mechanism, associated with anactivation energy of 181.9 kJ/mol. Interestingly with a decrease in grain size there was an increase in the structural distortion which resulted in a shift of Curie-temperature (phase transition) towards higher temperatures than that of conventional bulk ceramics. Extended Landau phenomenological theory for the ferroelectric particles was invoked to explain experimentally observed size dependent phase transition temperature and the critical size for SBT is predicted to be 11.3 nm. Grain size dependent dielectric, ferroelectric and piezoelectric properties of the SBT ceramics were studied and the samples comprising average grain size of 645 nm exhibited superior physical properties that include remnant polarization (2Pr) = 16.4 μC cm-2, coercive field (Ec) = 38 kV cm-1, piezoelectric coefficient (d33) = 22 pC N-1 and planar electromechanical coupling coefficient (kp) = 14.8 %. In Chapter 6, the studies pertaining to the fabrication of Sr(2-x)(Na0.5Bi0.5)xBi4Ti5O18 (SNBT) ceramics for various x values (0, 0.1, 0.25, 0.3, 0.4 and 0.5), using fine powders synthesized via sol-gel route are dealt with. X-ray powder diffraction, transmission electron microscopy and Raman spectroscopic studies were carried out to confirm composition dependent structural changes taking place in the SNBT ceramics. Scanning electron microscopic studies carried out on ceramics revealed that dopants played an important role in inhibiting the grain growth. Dielectric constants of the ceramics were found to decrease with an increase in ‘x’. The increase in Curie temperature with increase in ‘x’ is attributed to the decrease in the tolerance factor. Particularly,x = 0.3 composition of the SNBT ceramics exhibited better piezo and ferroelectric properties with a higher Curie-temperature (569 K). The piezoelectric coefficient (d33) and the planar electromechanical coupling coefficient (kp) of SNBT(x = 0.3) were enhanced by 25% and 42% respectively as compared to that of the undoped ceramics. Chapter 7 deals with the glasses in the system (100 –x) {Li2O + 2B2O3} ─x {2SrO + 2Bi2O3 +5TiO2} (where, x = 10, 25 and 35) fabricated via conventional melt-quenching technique. The amorphous and glassy characteristics of the samples were confirmed respectively using X-ray diffraction (XRD) and differential scanning calorimetric (DSC) methods. All the compositions under investigation exhibited two distinct crystallization peaks (exothermic peaks in the DSC traces): the first peak at ~ 545 °C and the second at ~610 °C that were found to be associated with the crystallization of the phases (as confirmed from the XRD studies) Sr2Bi4Ti5O18 (SBT)and Li2B4O7 (LBO) respectively. Non-isothermal crystallization kinetics (using modified Ozawa-type plots) for SBT crystallization in the LBO glass matrix for the compositions x = 10 and 35, indicated three dimensional growth of the crystallites from pre-existing nuclei present in the as-quenched samples and their effective activation energies for crystallization were found to be around 686 ± 85 kJ/mol and 365 ± 53 kJ/mol, respectively. The optical band gap of the as-quenched glasses for the composition x = 35 was 2.52 eV, is less than that of the composition x = 10 (2.91 eV). The Urbach energies for the as-quenched glasses of compositions x = 10, 25 and 35 were found to be 118 ± 2 meV, 119 ± 2 meV and 192 ± 1 meV respectively.The glasses associated with the composition x = 35, on controlled heat-treatment at 515 °C for various durations (1―20 h), yielded glass-ceramics comprising SBT nano-crystals (18―28 nm) embedded in the LBO glass matrix. Compressive strain in the nano-crystallites of SBT, analyzed using Williamson-Hall method was found to decrease with an increase in the crystallite size. The second harmonic generation signal (532 nm) intensity emanating from glass-nanocrystal composites comprising 22.1 nm SBT crystallites was nearly 0.3 times that of a KDP single crystal. Although each chapter is provided with conclusions and a list of references, thesis ends with a separate summary and conclusions.
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31

Shet, 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.

Full text
Abstract:
Ferroelectric materials are very promising for a variety of applications such as high-permittivity capacitors, ferroelectric memories, pyroelctric sensors, piezoelectric and electrostrictive transducers and electro-optic devices, etc. In the area of ferroelectric ceramics, lead-based compounds, which include lead zirconatetitanate (PZT) solid solutions, occupy an important place because of their superior physical properties. However, due to the toxicity of lead, there is an increasing concern over recycling and disposing of the devices made out of these compounds, which has compelled the researchers around the globe to search for lead-free compounds with promising piezo and ferroelectric properties. Ferroelectric materials that belong to Aurivillius family of oxides have become increasingly important from the perspective of industrial applications because of their high Curie-temperatures, high resistivity, superior polarization fatigue resistanceand stable piezoelectric properties at high temperatures. These bismuth layer-structured ferroelectrics (BLSF) comprise an intergrowth of [Bi2O2]2+ layers and [An+1Bn O3n+1]2- pseudo-perovskite units, where ‘n’ represents the number of perovskite-like layers stacked along the c-axis. ‘A’ stands for a mono-, di- or trivalent ions or a combination of them, ‘B’ represents a small ion with high valencysuch as Ti4+, Nb5+, Ta5+or a combination of them.Ferroelectricity in the orthorhombic phase of these compounds was generally attributed to the cationic displacement along the polar a-axis and the tilting of octahedra around the a- and c-axes. Sr2Bi4Ti5O18(SBT) is ann = 5 member of the Aurivillius family and possess promising ferroelectric and piezoelectric properties that could be exploited for a wide range of applications, including ferroelectric random access memories (FeRAM), piezoelectric actuators, transducers and transformers. Reports in the literaturereveal that the ferroelectricand piezoelectric properties of these oxides can be tuned depending on synthesis routes vis-a-vis micro-structural aspects (texture, grain size) and site specific dopant substitutions.In the present study, textured SBT ceramics were fabricated using pre-reacted precursors and their anisotropic dielectric, piezoelectric and ferroelectric properties were demonstrated. Grain size tunability with regard to their physical properties was accomplished in the ceramics, fabricated using fine powders obtained from citrate assisted sol-gel synthesis. The grain size dependent second harmonic generation activity of SBT ceramics was investigated. Enhancement in the piezoelectric and ferroelectric properties of SBT ceramics was achieved by substituting A site ions (Sr2+) with a combination of Na+ and Bi3+. From the perspective of non-linear optical device applications, physical properties associated with the SBT crystallized in a transparent lithium borate glass matrix were studied. The results obtained in the present investigations are organized as follows, Chapter 1 gives a brief exposure to the field of ferroelectrics. The emphasis has been on the ferroelectric oxides belonging to the Aurivillius family. Structural aspects and the underlying phenomena associated with ferroelectricity in these compounds are discussed. A brief introduction to the glasses, thermodynamic aspects of glass formation and fabrication of glass- ceramics are included. Basic principles involved in the non-linear optical activities are highlighted. Chapter 2 describes the various experimental techniques that were employed to synthesize and characterize the materials under investigation. The experimental details pertaining to the measurement of various physical properties are included. Chapter 3 deals with the fabrication of Sr2Bi4Ti5O18 ceramics using the pre-reacted Bi4Ti3O12 and SrTiO3 powders viasolid-state reaction route. These in stoichiometric ratio were uniaxially pressed and sintered at 1130oC for 3 h resulting in textured Sr2Bi4Ti5O18 ceramics. The obtained dense ceramics exhibited crystallographic anisotropy with prominent c-axis oriented grains (Lotgering factor of 0.62) parallel to the uniaxially pressed direction. The resultant anisotropy in the ceramics was attributed to the reactive template-like behavior of Bi4Ti3O12 that was used as a precursor to fabricate Sr2Bi4Ti5O18 ceramics. Dielectric, ferro and piezoelectric properties measured on the ceramics in the direction perpendicular to the uniaxially pressed axis were found to be superior to that measured in the parallel direction. Chapter 4 reports the details pertaining to the synthesis of strontium bismuth titanate (Sr2Bi4Ti5O18) powders comprising crystallites of average sizes in the range of 94–1400 nm via citrate-assisted sol-gel route. X-ray powder diffraction, Transmission Electron Microscopy (TEM) and Raman spectroscopy were employed for the structural studies. A crystallite size-dependent variation in the lattice parameters and the shift in the Raman vibration modes were observed. Second harmonic signal (532 nm) intensity of the Sr2Bi4Ti5O18 powders increased with the increase in the average crystallite size and the maximum intensity obtained in the reflection mode was 1.4 times as high as that of the powdered KH2PO4. Piezo force microscopic analyses carried out on an isolated crystallite of size 74 nm, established its single domain nature with the coercive field as high as 347 kV/cm. There was a systematic increase in the d33 value with an increase in the size of the crystallite and a high piezoelectric coefficient of ~27 pm/V was obtained from an isolated crystallite of size 480 nm. Chapter 5 illustrates the details concerning the fabrication of Sr2Bi4Ti5O18(SBT) ceramics with different grain sizes (93 nm–1.42 μm) using nano-crystalline powders synthesized via citrate assisted sol-gel method. The grain growth in these powder compacts was found to be controlled via the grain boundary curvature mechanism, associated with anactivation energy of 181.9 kJ/mol. Interestingly with a decrease in grain size there was an increase in the structural distortion which resulted in a shift of Curie-temperature (phase transition) towards higher temperatures than that of conventional bulk ceramics. Extended Landau phenomenological theory for the ferroelectric particles was invoked to explain experimentally observed size dependent phase transition temperature and the critical size for SBT is predicted to be 11.3 nm. Grain size dependent dielectric, ferroelectric and piezoelectric properties of the SBT ceramics were studied and the samples comprising average grain size of 645 nm exhibited superior physical properties that include remnant polarization (2Pr) = 16.4 μC cm-2, coercive field (Ec) = 38 kV cm-1, piezoelectric coefficient (d33) = 22 pC N-1 and planar electromechanical coupling coefficient (kp) = 14.8 %. In Chapter 6, the studies pertaining to the fabrication of Sr(2-x)(Na0.5Bi0.5)xBi4Ti5O18 (SNBT) ceramics for various x values (0, 0.1, 0.25, 0.3, 0.4 and 0.5), using fine powders synthesized via sol-gel route are dealt with. X-ray powder diffraction, transmission electron microscopy and Raman spectroscopic studies were carried out to confirm composition dependent structural changes taking place in the SNBT ceramics. Scanning electron microscopic studies carried out on ceramics revealed that dopants played an important role in inhibiting the grain growth. Dielectric constants of the ceramics were found to decrease with an increase in ‘x’. The increase in Curie temperature with increase in ‘x’ is attributed to the decrease in the tolerance factor. Particularly,x = 0.3 composition of the SNBT ceramics exhibited better piezo and ferroelectric properties with a higher Curie-temperature (569 K). The piezoelectric coefficient (d33) and the planar electromechanical coupling coefficient (kp) of SNBT(x = 0.3) were enhanced by 25% and 42% respectively as compared to that of the undoped ceramics. Chapter 7 deals with the glasses in the system (100 –x) {Li2O + 2B2O3} ─x {2SrO + 2Bi2O3 +5TiO2} (where, x = 10, 25 and 35) fabricated via conventional melt-quenching technique. The amorphous and glassy characteristics of the samples were confirmed respectively using X-ray diffraction (XRD) and differential scanning calorimetric (DSC) methods. All the compositions under investigation exhibited two distinct crystallization peaks (exothermic peaks in the DSC traces): the first peak at ~ 545 °C and the second at ~610 °C that were found to be associated with the crystallization of the phases (as confirmed from the XRD studies) Sr2Bi4Ti5O18 (SBT)and Li2B4O7 (LBO) respectively. Non-isothermal crystallization kinetics (using modified Ozawa-type plots) for SBT crystallization in the LBO glass matrix for the compositions x = 10 and 35, indicated three dimensional growth of the crystallites from pre-existing nuclei present in the as-quenched samples and their effective activation energies for crystallization were found to be around 686 ± 85 kJ/mol and 365 ± 53 kJ/mol, respectively. The optical band gap of the as-quenched glasses for the composition x = 35 was 2.52 eV, is less than that of the composition x = 10 (2.91 eV). The Urbach energies for the as-quenched glasses of compositions x = 10, 25 and 35 were found to be 118 ± 2 meV, 119 ± 2 meV and 192 ± 1 meV respectively.The glasses associated with the composition x = 35, on controlled heat-treatment at 515 °C for various durations (1―20 h), yielded glass-ceramics comprising SBT nano-crystals (18―28 nm) embedded in the LBO glass matrix. Compressive strain in the nano-crystallites of SBT, analyzed using Williamson-Hall method was found to decrease with an increase in the crystallite size. The second harmonic generation signal (532 nm) intensity emanating from glass-nanocrystal composites comprising 22.1 nm SBT crystallites was nearly 0.3 times that of a KDP single crystal. Although each chapter is provided with conclusions and a list of references, thesis ends with a separate summary and conclusions.
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