Dissertations / Theses on the topic 'CERAMICS DOPED'
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Turón, Viñas Miquel. "Mechanical properties of co-doped zirconia ceramics." Doctoral thesis, Universitat Politècnica de Catalunya, 2018. http://hdl.handle.net/10803/620660.
Full textL'òxid de zirconi estabilitzat amb un 3 mol% d'itria és una ceràmica policristal·lina amb estructura tetragonal (denominada freqüentment zircònia, o bé 3Y-TZP) presenta propietats molt interessants per a aplicacions biomèdiques degut a la seva biocompatibilidad i altes propietats mecàniques. Entre elles, destaca la seva alta tenacitat de fractura, la qual és deguda a la transformació de fase tetragonal a monoclínica (t-m) induïda sota tensió al voltant de la punta d'una esquerda. No obstant, els grans tetragonals superficials també poden transformar-se de forma espontània a fase monoclínica en ambients humits, fenomen conegut com a degradació a baixa temperatura (LTD, per les seves sigles en anglès), la qual és un problema important en aplicacions on l'aigua hi és present. Diversos mètodes s'han proposat per tal d'augmentar la resistència a la LTD de la zircònia, des de la millora dels processos de fabricació en termes de tamany de gra, densitat o tensions residuals, fins al dopatge de la zircònia amb altres òxids, com magnèsia o cèria. Particularment, la zircònia estabilitzada amb cèria (Ce-TZP) posseeix una alta resistència a la LTD i major tenacitat de fractura que la 3Y-TZP, però menor resistència a fractura i duresa, en part degut a la seva major grandària de gra. L'estratègia seguida en aquest treball consisteix en la millora de les propietats mecàniques de la Ce-TZP mitjançant la reducció de la grandària de gra, sense disminuir la resistència a la LTD. Amb aquest objectiu, partint de dues composicions de Ce-TZP (10 i 12 mol% de CeO2), s'han afegit diferents quantitats de CeO i de Y2O3 per a reduir el creixement de gra durant la sinterització i així augmentar la tensió crítica per a la transformació t-m, i per tant la resistència a flexió i duresa. Per altra banda, donat que la resistència a flexió ve determinada per la tenacitat de fractura d'esquerdes petites superficials, s'ha desenvolupat una metodologia reproduïble per a produir micro-entalles superficials mitjançant l'ablació làser de puls ultra-curt per així mesurar aquesta propietat. S'ha posat en relleu que amb la metodologia desenvolupada es produeixen esquerdes molt afilades i de dimensions de l'ordre de les esquerdes naturals presents. Els resultats posen de manifest que la tenacitat de fractura per esquerdes petites són molt diferents de les obtingudes per mètodes amb esquerdes grans o a partir del mètode d'indentació. Aquesta tesis és dipositada pel grau de doctor en el programa "Ciència i Enginyeria dels Materials" de la Universitat Politècnica de Catalunya com a compendi de publicacions. La investigació descrita en aquest treball es va desenvolupar per l'autor durant el període de desembre de 2012 a octubre de 2017 sota la supervisió del professor M. Anglada al Departament de Ciència dels Materials i Enginyeria Metal·lúrgica de la Universitat Politècnica de Catalunya, i durant tres estades d'investigació durant 2015, 2016 i 2017 (406 dies en total) al Departament de Ciència de Materials (MTM) de KU Leuven (Bèlgica), sota la supervisió del professor J. Vleugels. El treball descrit en aquesta dissertació és original, llevat quan es proporcionen referències detallades.
Tennakone, Harshani. "Barrier Layer Concepts in Doped BaTiO3 Ceramics." University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1367937169.
Full textGajum, Naima Ramadan. "Rare-earth doped (α'/β')-Sialon ceramics." Thesis, University of Warwick, 2001. http://wrap.warwick.ac.uk/3072/.
Full textWu, Patrick. "Composition-electrical property correlations of doped Na0.5Bi0.5TiO3 ceramics." Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/22024/.
Full textDang, Yun. "Electrical properties of pure and doped rutile ceramics." Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/21635/.
Full textCorreia, Tatiana Maria Pereira. "Lattice and relaxation mechanisms in doped SrTiO3 ceramics." Master's thesis, Universidade de Aveiro, 2008. http://hdl.handle.net/10773/2266.
Full textCerâmicas ferroeléctricas do tipo relaxador têm despertado um renovado interesse científico, devido às suas muitas aplicações em tecnologia: memórias dinâmicas de acesso aleatório, condensadores “bypass”, dispositivos com aplicações na gama das microondas, sensores piroeléctricos de baixa temperatura, etc. Estas aplicações estão associadas a problemas conceptuais, relacionados com a distribuição de agregados polares e suas interacções, e também com o efeito mediador das matrizes em que os agregados estão inseridos. Este trabalho tem como objectivo principal o estudo das propriedades polares de cerâmicas em matrizes altamente polarizáveis. Entre os materiais fortemente polarizáveis, os paraeléctricos quânticos são os que mais se destacam. São muito sensíveis a defeitos, impurezas, tensões e campos eléctricos. Um dos mais interessantes é o paraeléctrico quântico Titanato de Estrôncio (SrTiO3), que apresenta uma transição de fase paraantiferrodistorsiva a ~ 110 K e que para concentrações adequadas de dopantes podem ser induzidos estados ferroeléctricos ou do tipo relaxador, geralmente localizados a baixas temperaturas. Estes estados podem corresponder à activação de novas bandas Raman de primeira ordem, a valores elevados de constante dieléctrica e a diferentes processos de relaxação polares. Assim, este trabalho está focado no estudo comparativo da rede, das propriedades dieléctricas e de relaxação polar em cerâmicas de SrTiO3 dopadas com Ítrio, Lantânio e Manganês, designados pelos sistemas Sr1- 1.5xLaxTiO3 (x=0.0133, 0.0533 and 0.13), Sr1-1.5xYxTiO3 (x=0.005 and 0.01), Sr1- xMnxTiO3 (x=0.01, 0.02 and 0.05) and SrTi1-xMnyO3 (y=0.01 and 0.05). Estes sistemas foram sintetizados pelo método convencional. A sua microestrutura e a estrutura cristalográfica foram analisadas através de difracção de raios X, microscopia electrónica de varrimento e transmissão, assim como por espectroscopia de energia dispersiva. Estudos detalhados de dinâmica de rede e de processos polares foram realizados utilizando as técnicas de espectroscopia Raman e de Correntes Termicamente Estimuladas (CTE), num amplo intervalo de temperaturas variando entre 10 K e a temperatura ambiente. Os resultados experimentais foram analisados através de modelos teóricos e discutidos com base na estequiometria química, características dos iões e a sua localização na rede. Pretende-se, a partir do conjunto de resultados obtidos, compreender melhor as propriedades do Titanato de Estrôncio. Embora, a dinâmica da rede do Sr1- 1.5xLaxTiO3 (x=0.0133, 0.0533 and 0.0833) ter sido já estudada, o efeito da dopagem de Ítrio é ainda desconhecido. No presente estudo, propomos analisar o espectro Raman obtido em ambos os sistemas e diferentes concentrações, com o objectivo de clarificar o comportamento da rede do SrTiO3 aquando a dopagem por iões aliovalentes. Os resultados experimentais indicam que a substituição do ião de Estrôncio por iões de Lantânio e Ítrio, dá origem a novas bandas nos espectros Raman, devido à perda do centro de inversão originado pelo efeito de dopagem do Titanato de Estrôncio. Este facto permite o acesso ao comportamento das bandas activas em infravermelho, sendo assim possível obter informações relativas à existência de estados polares a baixas temperaturas. O amortecimento parcial do modo polar TO1 obtido em todos os sistemas estudados aponta para a ausência de uma fase ferroelétrica a baixas temperaturas, confirmando resultados publicados anteriormente. O desvio da temperatura de transição para-antiferrodistorsiva para temperaturas mais elevadas nos sistemas dopados com Ítrio e Lantânio mostra que Ta é fortemente dependente do factor de tolerância da estrutura. Apesar das mudanças observadas em Ta nos sistemas dopado de SrTiO3, o comportamento em temperatura do modo mole associado à transição de fase antiferrodistorsiva A1g, pode ser descrito em termos de uma lei de potência semelhante à lei utilizada em trabalhos previamente realizados no sistema de SrTiO3 não dopado. Observam-se ainda alguns modos de baixa frequência, que por não poderem ser identificados com nenhum modo da rede, podem efectivamente estar associados a efeitos de desordem originados pela presença dos iões dopantes nestes sistemas. Vários trabalhos focaram-se já no estudo do SrTiO3 dopado, contudo os processos de relaxação polar observados em alguns destes sistemas não foram ainda completamente analisados. Assim, os processos de relaxação polar observados nas cerâmicas de SrTiO3 dopadas com Lantânio,Ítrio e Manganês foram estudados a partir de medidas de Currentes Termicamente Estimuladas (CTE) na gama de temperatura 10-300 K. Os resultados experimentais obtidos foram analisados através de modelos de relaxação dipolar e cargas espaciais, com o objectivo de determinar a natureza dos processos de relaxação. Estes resultados revelam a existência de diferentes processos de relaxação localizados na gama de temperaturas estudada. Com base em resultados previamente publicados, os mecanismos de relaxação detectados por CTE nos sistemas estudados e que ocorrem a baixas temperaturas foram associados a mecanismos de origem dipolar, enquanto que aqueles que se observam a altas temperaturas foram atribuídos à deslocação de cargas espaciais. Os resultados obtidos nos sistemas em que o ião dopante substitui o catião no lugar A ou B da rede apontam para a existência de mecanismos de relaxação polares muito distintos. Considerando apenas os processos de tipo dipolar observados a baixas temperaturas, foi possível identificar os correspondentes mecanismos de relaxação e concluir que estes dependem principalmente do raio iónico do ião dopante e do nodo da rede onde a substituição ocorre. Esta técnica (CTE) não convencional tem revelado ser de grande interesse como complemento de resultados previamente obtidos por espectroscopia dieléctrica. Esta dissertação é constituída por quatro principais capítulos. O capítulo 1 inclui uma revisão da literatura sobre materiais relacionados com SrTiO3 e concluí com os objectivos deste trabalho. No capítulo 2 são apresentados resultados referentes à dinâmica da rede dos sistemas Sr1-1.5xLaxTiO3 e Sr1- 1.5xYxTiO3 obtidos por espectroscopia Raman. Ainda neste capítulo, é introduzido o fenómeno da difusão Raman e apresentada um estudo comparativo da transição de fase para-antiferodistorsiva e a natureza paraléctrica quântica destes dois sistemas. Uma técnica distinta foi também utilizada na identificação dos mecanismos de relaxação em cerâmicas de SrTiO3 dopadas: Correntes Termicamente Estimuladas (CTE). No capítulo 3, este método eficaz é descrito e aplicado no estudo das cerâmicas de SrTiO3 dopadas com Lantânio, Ítrio e Manganês. Neste capítulo é desenvolvida uma discussão geral que relaciona estes resultados com os resultados apresentados na literatura. A análise teórica dos resultados experimentais permitirá uma melhor compreensão dos processos de relaxação observados a partir da determinação dos parâmetros característicos, tais como a energia de activação e tempo de relaxação a temperatura infinita. Esta informação proporcionará a identificação dos mecanismos subjacentes ao comportamento de relaxador anteriormente observado. Finalmente, os resultados obtidos serão resumidos no capítulo 4, bem como apresentadas algumas sugestões de trabalho futuro. ABSTRACT: Ferroelectric ceramics and relaxors have awaken a renewed scientific interest, due to their many applications in technology: dynamic random access memories (DRAMs), bypass capacitors, tuneable microwave devices, low temperature pyroelectric sensors, etc. These applications are associated with conceptual problems, which deal with the distribution of polar aggregates and their interactions, and also with the mediator effects of the matrices in which the aggregates are inserted. This work is centred in the study of the properties of polar ceramics in highly polarizable matrices. Among the highly polarizable materials the quantum paraelectrics stand out. Their electrical properties are very sensitive to defects, impurities, stresses, and applied electric fields. One of the most interesting quantum paraelectrics is Strontium Titanate (SrTiO3), which presents a paraantiferrodistortive phase transition at ~110 K and atomic lattice substitutions can induce ferroelectric or relaxor states, commonly located at low temperatures. These may yield the activation of Raman first order bands, high dielectric constant values and distinct polar relaxation processes. Consequently this work is focused on the comparative study of the lattice, dielectric and polar relaxation properties of SrTiO3 ceramics doped with Yttrium, Lanthanum, and Manganese ions, namely Sr1-1.5xLaxTiO3 (x=0.0133, 0.0533 and 0.13), Sr1-1.5xYxTiO3 (x=0.005 and 0.01), Sr1-xMnxTiO3 (x=0.01, 0.02 and 0.05) and SrTi1-xMnyO3 (y=0.01 and 0.05) systems. These systems were synthesised by the conventional mixed oxide method. Their crystallographic and micro structures were analysed through X-ray diffraction, scanning and transmission electron microscopy, together with energy dispersive spectroscopy methods. Detailed studies of both lattice dynamics and polar relaxations processes have been carried out through Raman and Thermally Stimulated Currents techniques, in a wide interval of temperatures ranging between 10 K and room temperature. The experimental results have been analysed through comprehensive theoretical models, and discussed on the basis of charge and chemical stoichiometry, ion characteristics, and site occupancy. With the ensemble of these results it is expected to provide a better understanding of the physical properties of Strontium Titanate. Although, lattice dynamics of Sr1-1.5xLaxTiO3 (x=0.0133, 0.0533 and 0.0833) have already been reported, the Yttrium doping effect is still unknown. In the present work we propose to analyze Raman spectra for both systems and different concentrations in order to clarify the aliovalent doping behaviour on SrTiO3 lattice. The obtained results show that Lanthanum and Yttrium substitution gives rise to new features in the Raman spectra, due to the loss of the center of inversion originated by doping SrTiO3 ceramics. Those features enable us to have also access to the behavior of infrared active bands, which provides additional information regarding the existence of polar states at low temperatures. The absence of the softening of the TO1 polar mode in all the systems studied supports the non-existence of a ferroelectric phase at low temperatures, which has been reported previously. The shift of the para-antiferrodistortive transition temperature (Ta) towards higher temperatures on both Lanthanum, and Yttrium doped systems clearly evidences that Ta is strongly dependent on the structural tolerance factor. Despite the observed changes in Ta in doped SrTiO3, the temperature behaviour of the antiferrodistortive soft mode A1g can be described in terms of a power law as it has been previously reported for pure SrTiO3. Moreover some low frequency modes, which could not be assigned to other lattice modes, may be apparently associated with disorder effects, stemming from the presence of dopants ions. Although there are several works addressed to the study of doped SrTiO3 systems, the polar relaxation processes observed in some of these systems have not been fully investigated. Therefore, polar relaxation processes in La-, Y- and Mn- doped SrTiO3 ceramics were studied by undertaking Thermally Stimulated Currents (TSC) measurements from room temperature to 10 K. The experimental results were analyzed by using dipolar and space-charge relaxation models in order to determine the nature of the relaxation processes involved. The results reveal the existence of different relaxation processes within the studied range of temperatures. Whereas at low temperatures (18-80 K), relaxation mechanisms of dipolar type were disclosed, space-charge relaxation processes could be identified at higher temperatures (150-300 K) confirming the previous dielectric results. In addition differences in the relaxation processes are observed for different substitute site of the lattice. Regarding dipolar relaxation processes observed at low temperatures, we were able to identify the corresponding mechanisms, which mainly depend on the ionic size, charge and site occupancy. This non conventional technique (TSC technique) has revealed to be a powerful technique to complement the results previously obtained by dielectric spectroscopy. This thesis will comprise four main chapters. Chapter one includes a survey of literature addressing the background of SrTiO3-related materials and concludes with the aims and objectives of this work. Chapter 2 disclose the lattice dynamics of Sr1-1.5xLaxTiO3 and Sr1-1.5xYxTiO3 systems revealed by Raman spectroscopy. Here, Raman diffusion theory is briefly introduced as well as the experimental set-up used in this work. This chapter concludes with a comparison between both systems regarding the para-antiferrodistortive phase transition and quantum paraelectricity features. A different technique was used to identify relaxation mechanisms in doped SrTiO3: Thermally Stimulated Depolarization Currents (TSDC) technique. In Chapter 3, this powerful method is reviewed and applied to La-, Y- and Mn- doped SrTiO3 ceramics. This chapter outlines the general discussion and links the results to the literature survey from the Chapter 1. The theoretical analysis of the experimental data should enable us to gain a better understanding of the relaxation processes through the knowledge of their characteristic parameters such as the activation energy, and relaxation time at infinite temperature. This information will allow determining which mechanisms are underlying the relaxation behaviour previously reported. Finally, a summary of the results obtained for the studied systems is presented in Chapter 4, which ends with a few concluding remarks and directions for further work.
Liddicott, Katherine Mary. "High temperature materials chemistry of doped cerium oxide ceramics." Thesis, Imperial College London, 1994. http://hdl.handle.net/10044/1/8619.
Full textPerkins, James M. "Microstructure and properties of (rare earth) doped oxide ceramics." Thesis, University of Warwick, 2006. http://wrap.warwick.ac.uk/3705/.
Full textKukkonen, Liv Linnea. "Transparent, rare earth doped, oxyfluoride glass-ceramics for photonics." Thesis, University of Sheffield, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340220.
Full textBeggiora, Marco. "Characterisation of rare earth doped oxy-fluoride glass ceramics." Thesis, University of Sheffield, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401189.
Full textMouzon, Johanne. "Synthesis of ytterbium-doped yttrium oxide nanoparticles and transparent ceramics." Doctoral thesis, Luleå : Division of Engineering Materials, Luleå University of Technology, 2006. http://epubl.ltu.se/1402-1544/2006/64/.
Full textSakabe, Yukio. "Calcium-doped barium titanate ceramics for nickel electrode multilayer capacitors." 京都大学 (Kyoto University), 2003. http://hdl.handle.net/2433/149473.
Full textKalkhoran, Rahmati Behnaz. "Microstructural studies on the reoxidation behavior of Nb-doped SrTiO3 ceramics." Stuttgart : Max-Planck-Inst. für Metallforschung, 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=97316588X.
Full textWang, Yifeng, Kyu Hyoung Lee, Hiromichi Ohta, and Kunihito Koumoto. "Thermoelectric properties of electron doped SrO(SrTiO3)n (n=1,2) ceramics." American Institite of Physics, 2009. http://hdl.handle.net/2237/12629.
Full textBen, Liubin. "Synthesis and Characterisation of Rare-earth and Calcium Doped BaTiO3 Ceramics." Thesis, University of Sheffield, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.522567.
Full textKhan, 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.
Full textGonçalves, Tássia de Souza. "Rare earth doped fluorophosphate glass and glass-ceramics: structure-property relations." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/18/18158/tde-30102018-100600/.
Full textVidros e vitrocerâmicas fluorofosfatos dopados com íons terras raras (TR3+) estão entre os candidatos mais promissores para a geração de laser de alta eficiência na região espectral do infravermelho próximo. As vitrocerâmicas são materiais policristalinos com microestrutura bem definida obtida a partir da cristalização controlada do vidro base. Desenvolvendo vidros base de fluorofosfato com composições apropriadas e controlando a nucleação e crescimento de cristais, vitrocerâmicas com propriedades especiais podem ser fabricadas combinando as vantagens dos fluoretos (baixa energia de fônons, baixos índices de refração, janela ótica extensa, baixa higroscopicidade) e óxidos (alta estabilidade química e mecânica e alta solubilidade dopante), resultando no aumento das propriedades emissoras dos íons TR3+. Neste estudo, apresentamos a síntese por fusão/resfriamento e investigação estrutural/espectroscópica de novos vidros e vitrocerâmicas com composição 25BaF225SrF2(30-x)Al(PO3)3xAlF3(20-z)YF3: zREF3, onde x = 15, 20 ou 25, RE = Er3+ an / ou Yb3+ e Nd3+. Uma investigação estrutural detalhada de uma série destes vidros foi conduzida utilizando espectroscopias Raman, de ressonância magnética nuclear de estado sólido (RMN) e de ressonância paramagnética eletrônica (EPR).
Wang, Jing. "Investigation of rare earth-doped ceramics as thermal barrier coating materials." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/37230/.
Full textAbram, Edward John. "Synthesis and characterisation of doped lanthanum gallate and lanthanum silicate oxide-ion conductors." Thesis, University of Sheffield, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251374.
Full textMhaisalkar, Subodh G. "Dielectric properties and characterization of doped barium titanium(4)oxygen(9) ceramics /." The Ohio State University, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487681148542259.
Full textRahmati, Behnaz. "Microstructural studies on the reoxidation behavior of Nb-doped SrTiO 3 ceramics." [S.l. : s.n.], 2004. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB11514003.
Full textKoroglu, Ahmet. "Preparation and NMR characterisation of ceramic materials doped with '1'5N and '1'7O." Thesis, University of Newcastle Upon Tyne, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242346.
Full textKerman, Gozde. "The Effect Of Strontium-containing Silicon-doped Hydroxyapatite Ceramics On Bone Defect Healing." Phd thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12612971/index.pdf.
Full text0.02 g/cm2) bone mineral density values than the other groups 4 weeks after implantation however differences between groups were not significant in vivo. Sr-Si-HA and BMP-Sr-Si-HA composites stimulated new bone formation at cortical bone defects of tibia according to micro computerized-tomography and histological results. Findings of this study promote future research on Sr containing bioceramics in treatment of orthopedic problems.
Illingsworth, J. S. "Investigation of the grain boundary layer characteristics of donor doped barium titanate ceramics." Thesis, Durham University, 1990. http://etheses.dur.ac.uk/1118/.
Full textWu, Yun. "Study of vanadium doped strontium bismuth niobate tantalate ferroelectric ceramics and thin films /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/10581.
Full textNo, Young Jung. "Development and characterization of synthetic injectable biomaterials incorporated with doped calcium silicate ceramics." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/16949.
Full textLong, Phan The. "Synthesis and characterization of Mn-Doped ZnO sprintronic materials: Polycrystalline ceramics, thin films, and nanostructures." Thesis, University of Bristol, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492507.
Full textFujita, Shunsuke. "Development of Rare Earth Doped Active Glass-Ceramics for White Light Emitting Diode and Optical Telecommunications." Kyoto University, 2010. http://hdl.handle.net/2433/120435.
Full text0048
新制・課程博士
博士(人間・環境学)
甲第15469号
人博第499号
新制||人||122(附属図書館)
21||人博||499(吉田南総合図書館)
27947
京都大学大学院人間・環境学研究科相関環境学専攻
(主査)教授 田部 勢津久, 教授 杉山 雅人, 准教授 木下 俊哉
学位規則第4条第1項該当
Tovar, Vargas Daniela. "Processing, microstructure and mechanical properties of ceria-stabilized zirconia-based ceramics co-doped with calcia and alumina." Doctoral thesis, TDX (Tesis Doctorals en Xarxa), 2021. http://hdl.handle.net/10803/672340.
Full textEn los últimos años, las cerámicas de circona se han utilizado en muchas aplicaciones. Algunos de ellos incluyen el conformado de herramientas por su alta resistencia y tenacidad a la fractura, recubrimientos de barrera térmica en motores de turbinas por su baja conductividad térmica, como electrolito en la elaboración de Pilas de Combustible de Óxido Sólido (SOFC) por su alta conductividad iónica, y en la fabricación de implantes dentales por su biocompatibilidad y su apariencia estética. La circona biomédica es principalmente circona tetragonal dopada con un 3% molar de itria (3Y-TZP). Sin embargo, es sensible al fenómeno de degradación hidrotérmica. Esta es la razón para investigar el procesamiento y las propiedades mecánicas de la circona dopada con ceria, debido a su alta resistencia al envejecimiento. Sin embargo, la circona dopada con ceria presenta baja resistencia mecánica debido a su gran tamaño de grano. Se han dedicado muchos estudios a encontrar una forma de reducir el tamaño de grano. Se han propuesto varios métodos, como la adición de un estabilizador, o una segunda fase, la mejora del procesamiento del polvo o la modificación de las condiciones de sinterización. Siguiendo las ideas anteriores, esta tesis tiene como objetivo reducir el tamaño de grano en cerámicas 10Ce-TZP (10% mol de CeO2), con el objetivo de aumentar la resistencia mediante tres estrategias diferentes. La primera estrategia ha sido la fabricación de compuestos con adición de alúmina (a-Al2O3) mediante procesamiento coloidal. La segunda estrategia ha sido utilizar óxido de calcio (CaO) como co estabilizador y añadir alúmina (a-Al2O3) como segunda fase. La tercera estrategia dirigida a mejorar el procesamiento mediante la combinación de molienda de bolas, moldeo por barbotina y posterior molienda de polvo. En todos estos estudios se ha realizado una caracterización microestructural, y mecánica. También se ha medido la degradación hidrotérmica para evaluar la resistencia de los compuestos elaborados al envejecimiento. Los resultados obtenidos en las dos primeras estrategias mostraron una reducción del tamaño de grano, lo que condujo a un aumento de la dureza y la resistencia. Sin embargo, en la tercera estrategia, el tamaño de grano no se redujo tanto como en las estrategias anteriores, lo que permitió obtener una tenacidad a la fractura moderada y un ligero aumento de dureza y resistencia en comparación con el material base 10Ce-TZP. Se logró una alta resistencia a la degradación hidrotérmica para todos los compuestos elaborados en todas las estrategias.
Ciència i enginyeria de materials
Kitaoka, Kenji. "Studies on the sol-gel synthesis of ceramics and dye-doped glasses aiming at advanced optical devices." 京都大学 (Kyoto University), 2002. http://hdl.handle.net/2433/149842.
Full textWillis-Ott, Christina. "Ytterbium-doped fiber-seeded thin-disk master oscillator power amplifier laser system." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5890.
Full textPh.D.
Doctorate
Optics and Photonics
Optics and Photonics
Optics
Corral, Jessica Olga. "Preparation of rare-earth (Eu3+, Tb3+, and Yb3+) doped Y2O3 luminescent ceramics by the use of reverse micelles." abstract and full text PDF (free order & download UNR users only), 2004. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1434067.
Full textSun, Qianying. "Conducting ceramics based on ZnO co-doped by (Al, Ti, Mg) : microstructure, electronic active defects and electrical properties." Thesis, Le Mans, 2020. http://www.theses.fr/2020LEMA1014.
Full textZnO based ceramics with appropriate doping elements show excellent electrical and optical properties such as high exciton binding energies, a modulated optical transparency and high electrical conductivities. Therefore, ZnO based conducting ceramics have been extensively investigated in the aim of their application as resistors, visitors, gas sensors, transparent electrodes, solar cell windows, piezoelectric, electro-optical and thermoelectric devices. The high conductivity of ZnO ceramics up to 0.1MS·m-1 is closely related to the doping elements along with the ceramic microstructure and the processing conditions with particular effects of grain boundaries, crystalline structure and structural disorder within the ceramics. Thus, the present thesis is devoted to the fabrication by sintering under defined conditions (sintering atmospheres, processes) of ZnO based ceramics co-doped by (Al, Ti, Mg) , the investigations and deep analysis of their related properties including crystalline structure, micro-structure and the electrical behavior. Exhaustive studies were developed on the doped ceramics by using structural methods (XRD, Raman), microscopy (TEM, SEM) and magnetic resonance (EPR, NMR) probing the local order and electronic active defects. The conductivity is adjusted by the nature of the structure influenced by the doping elements, the sintering atmosphere, and the sintering method. The correlation "Preparation - Structure - Conductivity" has been established to pave the way for the potential technological applications of highly conducting ZnO-based ceramics
Czerepinski, Jennifer H. "Mixedness determination of rare earth-doped ceramics." 2009. http://hdl.rutgers.edu/1782.2/rucore10001600001.ETD.000050502.
Full textLee, Hwan-wen, and 李煥文. "Acceptor-doped and co-doped BaTiO3 ceramics for MLCC applications." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/17348132889112611331.
Full text國立中山大學
材料與光電科學學系研究所
100
It is particularly intriguing in the role of the solid-state dopants, which are not only responsible for the semiconductivity, but also the dielectric properties of BaTiO3 ceramics, e.g. CaO, MgO, Y2O3, CoO and MnO2 for EIA-X7R characteristics. We have chosen to investigate three important processing parameters, oxygen partial pressure (pO2) for sintering, and two alkali-earth-metal oxides, i.e. CaO and MgO for solid-state additives in order to study how microstructure and dielectric properties are determined by them. They are used in MLCC industry for the effect in attaining X7R characteristics and protecting against or improving for dc degradation. Apart from establishing the temperature-dependent dielectric properties, i.e. temperature-coefficient of capacitance (TCC), for both qualitative and quantitative analysis, crystalline phases in sintered ceramics of tetragonal mixed with cubic, orthorhombic and rhombohedral phases are studied using XRD and Raman spectroscopy. For microscopic studies, SEM and TEM techniques, e.g. CBED and LACBED, combined with EDS are used to study phases both in core-shell. We will examine and confirm the fidelity of whether core-shell grains are induced by chemical inhomogeneity, and more importantly, if the diffuse phase transition is caused by such microstructure with direct observations, as previous studies in perovskite-related ceramics, and crystalline phase determination for these grains. It is also an objective that we investigate why and how, by what mechanism, the chemically similar alkali-earth metal oxides should impart completely different (and indeed opposite) effect in protecting against dc degradation. Keywords: MLCC, dc degradation, DPT, Raman spectroscopy, electron microscopy.
Tsai, Ming-chou, and 蔡銘洲. "Phase transition of the Li-doped and Bi-doped Silver Niobate Ceramics." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/91614634994613976429.
Full text國立臺南大學
材料科學系碩士班
96
This research is composed of two parts. First, the ceramics of Ag1-xLixNbO3(ALN) solid solution were sintered for Li concentration range 0≦x≦0.1. We investigate the phase transition behavior and dielectric properties of Li-doped with different concentration by using XRD、SEM、DSC、dielectric constant and Raman scattering. As a result, with increasing lithium contents, the phase transition of M1-M2 was shifted to lower temperature while the phase transition of M3-O1 was shifted to higher temperature. The orthorhombic symmetry was changed to tetragonal symmetry when x is greater than 0.05. The maximum value of the dielectric constant at x=0.05 was 400, and the dielectric loss value was controlled below 5%. Second, the ceramics of Ag1-yBiy/3NbO3 solid solution were sintered for Bi concentration range 0≦y≦0.15. Using the same analytic instruments, we investigate the phase transition behavior and dielectric properties of Bi-doping with different concentration. Room and high temperature phase transition were shifted to lower temperature by Bi-doping. Phase transition points were shifted to become fast and the phase structure was changed toward tetragonal symmetry after y>0.15. In addition, the value of dielectric loss was controlled below 0.2% from 250K to 450K.
Han, Jiaping. "Sintering and electrical properties of Mn-doped and Al-doped ZnO ceramics." Master's thesis, 2001. http://hdl.handle.net/10773/24986.
Full textOs materiais cerâmicos baseados em ZnO têm sido objecto de estudo intenso devido às suas propriedades encontrarem larga aplicação tecnológica. O estudo da sinterização e das propriedades eléctricas do ZnO dopado é relevante pelas suas potenciais aplicações, nomeadamente em cerâmicos de resistência variável com a tensão (varistores). Neste contexto, o presente trabalho debruçou-se sobre os sistemas binários Mn-ZnO e Al-ZnO, já que ambos os dopantes são utilizados na formulação química daqueles materiais. Prepararam-se amostras de ZnO puro e dopado com manganês e alumínio pela via convencional de preparação de cerâmicos, usando para a incorporação dos dopantes soluções etanólicas de Mn(NO3)2.4H2O e Al(NO3)3.9H2O. Para clarificar os efeitos de solução sólida e de segundas fases na sinterização e nas propriedades eléctricas do ZnO, investigaram-se os aspectos microestruturais e cristalográficos das amostras dopadas com as técnicas de XRD e SEM e TEM com EDS acoplado. Os resultados mostraram que no ZnO dopado com Al forma-se uma segunda fase de espinela, ZnAl2O4, a ~800ºC, que é estável a temperaturas mais elevadas. Determinou-se um limite de solução sólida de cerca de 600 ppm em Al no ZnO a 1200ºC. No ZnO dopado com Mn forma-se uma segunda fase cúbica de ZnMnO3 a temperaturas iguais ou inferiores a 450ºC e que se transforma noutra segunda fase tetragonal de ZnMn2O4 a ~1100ºC. As segundas fases dissolvem-se gradualmente na fase de ZnO e a 1200ºC já não se detectam segundas fases nas amostras com teores de manganês iguais ou inferiores a 1,2 mol%. Investigou-se a densificação e o crescimento de grão do ZnO dopado com Al, de 0,08 a 1,2 mol%, durante a sinterização isotérmica entre 1100º e 1400ºC. A dopagem com Al inibe significativamente o crescimento de grão do ZnO e aumenta o expoente do crescimento de grão de 3, no ZnO puro, para 4- 6 no ZnO dopado com Al. A energia de activação do crescimento de grão também varia de ~200 kJ/mol, no ZnO puro, para ~480 kJ/mol no ZnO dopado com Al. A análise microestrutural mostrou que as partículas de espinela, ZnAl2O4, exercem uma travagem efectiva na migração das fronteiras de grão no ZnO dopado com Al. A análise do efeito da dopagem com Al na velocidade de densificação evidenciou também a redução da força motriz para a densificação pelas partículas da segunda fase de espinela. Foi proposto um mecanismo de travagem do movimento da superfície dos poros na densificação, equivalente ao efeito de arrastamento-travagem exercido pelas partículas de segunda fase nas fronteiras de grão, durante o crescimento de grão.
Mestrado em Engenharia de Materiais
YI, TING, and 丁翊. "Photovoltaic responses of (Na0.5Bi0.5)TiO3-doped BiFeO3 ceramics." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/55835820632365770842.
Full text輔仁大學
物理學系碩士班
102
This work study BiFeO3-100x% (Bi0.5Na0.5)TiO3 (x=0.005,0.05) multiferroic ceramics and their photovoltaic responses, structure, dielectric permittivity, conductivity, magnetic properties, ferroelectric, and X-ray absorption spectroscopy. Open-circuit voltage, short-circuit current, and the I-V curve without illumination had been measured, using P-N junction model to do the data fitting. Ferroelectric (Bi0.5Na0.5)TiO3 doping maybe can do the high E-field poling in order to increase the conversion efficiency. Use XRD & SEM to analyze the structure, α angle, and lattice parameter at plane (110), and to compare the grain sizes due to different NBT compounds. The temperature point closes to the Nèel temperature (TN), suggested the magnetoelectric coupling. Conductivity can be calculate by the imagine part of dielectric permittivity. The enhanced ferromagnetism in BFO-5%BNT may due to variation of oxidation valences of Fe ion (Fe3+=>Fe4+) and/or the angle changing of Fe-O-Fe, we use the X-ray absorption spectroscopy to determine.
Tsai, Hung Jen, and 蔡鴻仁. "Effects of (Sr,Ca)TiO3 Ceramics Doped Additives." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/92690945269471529831.
Full textBhowmick, Luna. "Synthesis and characterization of La doped Bi4Ti3O12 ceramics." Thesis, 2012. http://ethesis.nitrkl.ac.in/3405/1/THESIS_LUNA.pdf.
Full textHuang, Tsung-de, and 黃琮德. "Preparation and Physical Properties of Bisumth-doped and Magnesium-doped Strontium Titanate Ceramics." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/89989659698092982985.
Full text國立臺南大學
材料科學系碩士班
98
SrTiO3 is an excellent candidate system in lead-free ceramic materials because of its a wide range of applications in integrated microelectronics. Recently, there has been an increasing interest in strontium titanate materials for microwave tunable applications, such as frequency-tunable resonators and filters operating in the GHz range. In this work, the Sr1-1.5xBixTiO3 and Sr1-xMgxTiO3 ceramics have been prepared by solid-state reaction method. Effect of the bisumth and magnesium content on the crystal structure and dielectric properties of ceramic were studied. This work is composed of two parts. First, the ceramics of Sr1-1.5xBixTiO3 solid solution were sintered for bismuth concentration range 0≦x≦0.1. could be successful synthesized in this work, and investigated the phase transion and dielectric properties of Bi-doped with different concentraction by using X-ray diffraction, SEM, DSC, dielectric constant and Raman scattering. As a result, the x-ray diffraction and Raman scatting profiles of Sr1-1.5xBixTiO3 are characteristic of the coexistence of cubic and orthorhombic, with increasing bismuth contents at x≧0.05. The formation of solid solution is restricted to x≦0.02;The maximum value of dielectric constant at x=0.05 was 1200. The phase transition point shifts to high temperature as bismuth content increases. Second, the x-ray diffraction and Raman scatting profiles of Sr1-xMgxTiO3 are characteristic of the coexistence of cubic and hexagonal, with increasing magnesium contents at x≧0.1. The formation of solid solution is restricted to x≦0.1. Mg doping itself does not induce ferroelectricity or a relaxor-like behavior in strontium titanate.
Li, Han, and 李含. "Preparation and Physical Properties of Potassium-doped and Lithium-doped Sodium hexatitanate Ceramics." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/05984742671631931715.
Full text國立臺南大學
材料科學系碩士班
99
Na2Ti6O13 is an excellent candidate system as lead-free dielectric materials at present years because it will not cause the problem of lead pollution. In this study, Na(2-x)KxTi6O13 and lithium sodium titanate ceramics have been prepared by solid-state reaction method. Effects of the potassium and lithium content on the dielectric properties of ceramics were studied. This study is composed of two parts. First, Na(2-x)KxTi6O13 had successful synthesized. The phase transition and dielectric properties was investigated by X-ray diffraction, Raman scattering, SEM , impedance analyzer and density measurements. The crystal maintains monoclinic structure for different compositions. The peak belongs to K2Ti6O13 starts to appear at x=1.2 from Raman scattering results. Second, lithium sodium ceramics had synthesized in this research, dielectric properties measure results show that the samples with Li/Na molar ratio 1:4 have high dielectric constant.
Hong, Ying-kai, and 洪英凱. "Preparation and Physical Properties of Potassium-doped and Lithium-doped Bismuth Sodium Titanate Ceramics." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/18389972862510486243.
Full text國立臺南大學
材料科學系碩士班
97
(Bi0.5Na0.5)TiO3 is an excellent candidate system in lead-free piezoelectric materials system at present because of its no lead pollution. In this research, the [Bi0.5(Na1-xKx)0.5]TiO3 and [Bi0.5(Na1-xLix)0.5]TiO3 ceramics have been prepared by solid-state reaction method. Effect of the potassium and lithium content on the crystal structure and dielectric properties of ceramics were studied. This research is composed of two parts. First, [Bi0.5(Na1-xKx)0.5]TiO3 could be successful synthesized in this research, and the phase transition and dielectric properties was investigated by X-ray diffraction, Raman scattering, SEM and impedance analyzer. X-ray diffraction and Raman scattering results show that increasing of potassium content makes the crystal structure change from cubic to tetragonal. The transition point shifts to high temperature as potassium content increases. Second, [Bi0.5(Na1-xLix)0.5]TiO3 could be successful synthesized in this research, X-ray diffraction results show that two phases mix together between x=0.3 and x=0.9. The transition point shifts to high temperature as the lithium content increases, and the dielectric peak becomes broaden.
Huang, Chen-Tsai, and 黃振財. "Crystallization and Optical Propertiesof Cr3+-doped Mullite Glass-Ceramics." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/66479934645692170250.
Full text大同大學
材料工程學系(所)
92
Mullite glass-ceramics doped Cr3+ to be possible to apply to being possible to adjust the laser and the solar concentrators. This study is SiO2-Al2O3-B2O3-ZnO-K2O in the fixed parent glass the ingredient, doped different content of the Cr2O3, after the suitable heat treatment, produces nano- size mullite crystallization pellet in the glass. Cr produces matter of the Luminescence, but Cr also possibly affects the nucleation and the crystal behavior, then influence microstructure and properties. Therefore changes content of the Cr2O3, discusses whether can further promote the properties. When DTA analysis, along with Cr2O3 by 0 increase to 0.5, Tp can reduce advances again, but when 0.25, Tp has the minimum value. In the XRD analysis, the increase content of the Cr2O3, second the stages heat treatments after nucleation - growth, forms the glass-ceramics, the main crystallization phase is the mullite. In the UV- visible and the infrared transmission analysis, is worthy of looking at increases Cr2O3 the glass -ceramics to have the absorption phenomenon in the visible, but not obviously absorbs in the near-infrared. In the Photoluminescence analysis, increases 0.1 Cr2O3 the mullite glass ceramics, increases along with nucleation temperature and the nucleation time, the crystal size changes small and the crystallized amount increases. Then increases along with crystallization temperature and crystallized amount, the emission intensity is bigger.
Chang, Jung Pang, and 張榮邦. "The effects of additives on Nb-doped titania ceramics." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/44607524349798729989.
Full text國立清華大學
材料科學(工程)研究所
82
Yan等人曾做出(Nb,Ba)-doped的TiO2變阻器,其非線性指數α,約3-4。 本研究藉由添加Al到(Nb,Ba,Si)-doped的TiO2,探討不同的 Al添加量及 燒結溫度,對於其電性的影響。結果發現,隨著適量Al的添加,變阻特性 變佳。(0.25% Nb,1% Ba,0.3% Si,0.15% Al)-doped的TiO2於1250℃燒結2 小時,可得到α值為7的變阻器。而隨著Al添加,電子傳導的熱活化能提 高,空乏區變厚,電容值下降,而散逸因子在低頻區則降低很多,但晶粒 半導化則變差。故過多的Al添加(0.2%以上)則變阻性不復存在。 @ 低 價位的Fe3+其離子半徑與Ti4+相近,易溶入晶粒中,抵消一些半導化。微 量的(約0.01%到0.025%)Fe3+添加,能使(0.25% Nb, 1% Ba, 0.3% Si, 0.15% Al)-doped的TiO2於1300℃燒結2小時後,熱活化能由 0.37eV提升 至0.4eV附近,而空乏區厚度亦稍增加故α值可從7提升至9。隨著Fe3+添 加量的增加散逸因子弛緩峰向低頻移動,晶粒半導化的程度變差,過量的 Fe3+(0.05%以上)將使變阻特性變得不明顯,甚至消失。
Rath, Durga Prasad. "Phase Evolution in Doped Polymer Derived Silicon Oxycarbide Ceramics." Thesis, 2015. http://ethesis.nitrkl.ac.in/6834/1/PHASE_Rath_2015.pdf.
Full textChang, Shan-Li, and 張善理. "The Study of MCAS Glass-doped Al2O3-TiO2 Microwave Ceramics." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/79722306985586466023.
Full text國立中山大學
電機工程學系研究所
90
Microwave dielectric resonators (DRs) are being widely used in microwave telecommunication devices owing to their excellent characteristics of suitable dielectric constant, good temperature stability, and low dielectric loss. In this study, the crystalline phase and the microwave dielectric properties of the (1-x)Al2O3 - xTiO2 (x=0.08, 0.12, 0.16) compositions with 2wt%, 4wt%, 6wt%, and 8wt% MgO-CaO-Al2O3-SiO2 (MCAS) glass addition have been investigated. By combining the material Al2O3 with negative temperature coefficient of the resonant frequency (τf = -55 ppm/℃) and the material TiO2 with positive τf value (τf = +450 ppm/℃), it is desired to produce the ceramics with τf ~0 ppm/℃. The MCAS is used as liquid-phase sintering aid to lower down the sintering temperature. In the MCAS-doped (1-x)Al2O3 - xTiO2 system, the Al2TiO5 phase starts to appear at about 1250℃, and then the crystalline intensity of Al2TiO5 phase increases with the increase of sintering temperatures and MCAS glass content, until the temperatures that TiO2 is consumed. As the sintering temperature increases, the maximum dielectric constants and Q×f values can be obtained at 1250℃, and the τf values shift from positive to negative. The optimum τf value of —0.6 ppm/℃ exists in the 88mol%Al2O3 - 12mol%TiO2 composition with 2wt% MCAS addition and sintering temperature of 1300℃. The MCAS content, TiO2 content, and sintering temperature will result in the variation of microwave dielectric properties. In this study, MCAS-doped (1-x)Al2O3 - xTiO2 system exhibits the microwave dielectric properties of: εr=7~9.5, Q×f=6500~11000, and τf = -60 to +40ppm/℃. By adjusting the MCAS content, TiO2 content, and sintering temperatures, ceramics with good microwave properties can be obtained in the MCAS-doped (1-x)Al2O3 - xTiO2 system.
Lee, Jian-han, and 李建翰. "Physical properties of the Li-doped Silver Tantalum Niobate Ceramics." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/13988782604628792929.
Full text國立臺南大學
材料科學系碩士班
99
This research is composed of two parts. First, the ceramics of AgNbO3 sintered for 1000℃,1050℃,1100℃ and 1200℃ are investigated by XRD、SEM、DSC、dielectric constant and Raman scattering to evaluate. Second, the phase transition behavior ceramics of Ag1-xLixNb0.9Ta0.1O3 solid solution were sintered for Li concentration range 0≦x≦0.15. We investigate the phase transition behavior and dielectric properties of Li-doped with different concentration by using XRD、SEM、DSC、dielectric constant and Raman scattering. As a result, we can find the powder have excellent perovskite structure,with increasing lithium contents the vibrational mode is increase. M3-O1 and O2-T phase transition temperature is increase. The maximum value of the dielectric constant at x=0.1 was 1273, and the dielectric loss value was controlled below 0.008.
Szu-MinChen and 陳思敏. "Impedance Spectroscopy Analysis of Mn-Doped Barium Calcium Titanate Ceramics." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/ze4zpz.
Full text國立成功大學
資源工程學系
106
In this study, calcium-doped barium titanate (BCT) powders were used as the raw materials to study different amounts of acceptor doping effects on the microstructure, crystal structure, and electrical properties of BCT. The A/B ratio of (Ba0.92Ca0.08)Ti1.005O3 was set for Ti-excess to prevent Ca doping onto the B-site. Powder of (Ba0.92Ca0.08)Ti1.005O3 was calcined at 1100°C which temperature can make the powder no second phase. Based on the Rietveld analysis results, Ca in the BCT mainly entered A-site to replace Ba. To simulating the MLCC sintering condition, the BCT ceramics should be sintered in reduction atmosphere to prevent the Ni electrode oxidation, and we also add different amounts of MnCO3 as acceptor to prevent the ceramic samples from semiconduction. The grain sizes after sintering are approximately 0.36 μm which fits the MLCC condition. In this study, We use two RQ equivalent circuit model to fit the impedance spectroscopy data, and the results meet the Curie-Weiss behavior. According to the impedance spectroscopy data, the grain and grain boundary conductivity of acceptor-doped BCT ceramics is determined by Vo ̈ and e' respectively. With the increase of the amount of addition, the grain and the grain boundary conductivity tends to increase. The similar grain and grain boundary conductivity of BCT ceramics are due to maintain the electric neutrality. While the depletion layer and grain boundary barrier height are tend to decrease as the amounts of acceptor increase. The comprehensive conclusions show that the amounts of acceptor (MnCO3) has a certain influence on the electrical analysis calculated by the impedance spectroscopy analysis.
Yu, Jian-Yi, and 余建逸. "Fabrication and properties of La and Ti doped Sr2Nb2O7 ceramics." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/d5am49.
Full text崑山科技大學
電子工程研究所
102
Thermoelectric materials gain much attentions in energy saving and environmental issues recently. They can capture electric power from waste heat or transfer electricity to cryogenic function. Their apparent thermoelectric properties or the so-called figure of merit Z can be improved by lowering the thermal conductivity of the materials. This leads us to find the Sr2Nb2O7 ceramic with low thermal conductivity. We try to dope the ceramics to increase their electric conductivity, which maybe even turn into semiconducting, while keeping their low thermal conductivity simultaneously. Therefore, excellent thermoelectric ceramics with high figure of merit Z were explored in this study. Fabrication and thermoelectric properties of La- and Ti-doped Sr2Nb2O7 ceramics was conducted in this study. The Sr2Nb2O7 ceramics was prepared by reaction sintering process, which is similar to conventional oxide route process but deleting the calcination process. The effects of sintering temperatures and soaking times on the microstructures and thermoelectric properties were investigated. The results show that no second phase exhibits in La and Ti doped Sr2Nb2O7 ceramics. The bulk density of La-doped and Ti-doped Sr2Nb2O7 ceramics increases with increasing sintering temperature up to 1350℃ and 1400℃ respectively, and remains nearly the same with further increasing temperature. Surfaces of the Sr2Nb2O7 ceramics show significant grain growth with increasing sintering temperature, but La-doping and Ti-doping seem to suppress grain growth relatively, which result in large number of crystal grains and grain boundaries. The huge grain boundaries are expected to affect conductivities and heat resistance of the ceramics.