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CaCu3Ti4O12 (CCTO), an unusual perovskite-like material, is known for extraordinarily high (often reaching 104) and relatively frequency independent dielectric constant. Recently, it has drawn a lot of attention, because of its potential applications in microelectronics and microwave devices. / In this investigation, CCTO powders were synthesized by two routes, a conventional solid-state reaction and a wet-chemistry method. Three kinds of materials, polyvinyl alcohol (PVA, an organic binder), boric oxide (B 2O3, a well-known glass former), hafnium oxide (HfO 2, a material with high dielectric constant ∼25), were added to the pre-reacted CCTO powder and sintered into ceramics. The effects of these additives on the microstructures, or electric and dielectric properties of CCTO ceramics were investigated. In addition, CCTO thin films were also successfully prepared. The AC conductivity, impedance, and complex dielectric permittivity were used to analyze the data. These observations were well explained in terms of an internal barrier layer capacitor (IBLC) model with Maxwell-Wagner (MW) dielectric relaxation. / Yuan, Wenxiang = 高介電常數材料CaCu₃Ti₄O₁₂χχχ / 苑文香. / Adviser: S.K. Hark. / Source: Dissertation Abstracts International, Volume: 73-01, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / Yuan, Wenxiang = Gao jie dian chang shu cai liao CaCu₃Ti₄O₁₂ de yan jiu / Yuan Wenxiang.

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Yuan, Wenxiang = CCTO陶瓷材料的制备和性质研究 / 苑文香. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (leaves 63-67). / Text in English; abstracts in English and Chinese. / Yuan, Wenxiang = CCTO tao ci cai liao de zhi bei he xing zhi yan jiu / Yuan Wenxiang. / Acknowledgement --- p.ii / Abstract --- p.iii / Contents --- p.v / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Background --- p.1 / Chapter 1.2 --- Structure --- p.1 / Chapter 1.3 --- Models --- p.3 / Chapter 1.3.1 --- Parallel RC --- p.3 / Chapter 1.3.2 --- Two parallel RCs in series --- p.5 / Chapter 1.4 --- Motivation --- p.7 / Chapter 1.5 --- Our work --- p.7 / Chapter Chapter 2 --- Experiment --- p.8 / Chapter 2.1 --- Sources and substrate --- p.8 / Chapter 2.2 --- Preparation of the CCTO samples --- p.8 / Chapter Chapter 3 --- Experimental equipment --- p.13 / Chapter 3.1 --- Furnace --- p.13 / Chapter 3.2 --- X-ray diffraction (XRD) --- p.13 / Chapter 3.3 --- Scanning electron microscopy (SEM) --- p.16 / Chapter 3.4 --- Impedance analyzers --- p.17 / Chapter Chapter 4 --- Selections of the experimental conditions --- p.18 / Chapter 4.1 --- Selection of calcining-process conditions --- p.18 / Chapter 4.1.1 --- Experimental results --- p.18 / Chapter 4.1.2 --- Comparison with the results of other research groups --- p.21 / Chapter 4.2 --- Selection of sintering-process conditions --- p.22 / Chapter 4.2.1 --- CuO volatilization --- p.22 / Chapter 4.2.2 --- CCTO decomposition --- p.24 / Chapter 4.3 --- Optimizing of the Cu/Ca ratio --- p.29 / Chapter Chapter 5 --- Results and discussion --- p.31 / Chapter 5.1 --- Properties of CCTO ceramics sintered at different temperatures for 10 h --- p.32 / Chapter 5.2 --- Properties of CCTO ceramics sintered for different durations at 1000°C --- p.43 / Chapter 5.3 --- Properties of CC3+ΧTO ceramics --- p.52 / Chapter 5.4 --- Discussion --- p.58 / Chapter Chapter 6 --- Conclusions --- p.61 / References --- p.63

The positive temperature coefficient of resistivity (PTCR) sensors is resistor materials that undergo a sharp change in resistivity at a designed Curie temperature due to its unique structure and chemical composition. This effect serves important control functions in a wide variety of electronic circuitry and similar applications. Conventional calcining of mixed oxides method (CMO) is used for fabricating lanthanum doped barium titanate (BaTiO3) for PTCR behaviour through solid-state-sintering route, at 1100°C, 1350°C. Two batches of samples were fabricated at low and high sintering temperatures of 1100°C, 1350°C respectively. The effect of different concentrations of donor dopant on BaTiO3 on the electrical properties of Ba(1-x)LaxTiO3 with x= 0.0005, 0.001, 0.002, 0.0025, 0.003 mol%, is investigated at low sintering temperature. The influence of lantanum doping with Al2O3+SiO2+TiO2 (AST) as sintering aids on the electrical properties of Ba(1-x)LaxTiO3 with x= 0.0005, 0.001, 0.003 mol%, is also investigated. The results of the electrical characterization for the first batch of samples showed an increase in room temperature resistance with increaisng donor concentration. Also the results of the electrical characterization for the second batch of samples also showed the same increase in room temperature resistance with increasing donor concentration. For first batch of sensors the high room temperature resistance keeps the jump small and these materials showed V-shaped NTCR-PTCR multifunctional cryogenic sensor behavior with a strong negative coefficient of resistance effect at room temperature.Where as the second batch of sensors showed few orders of magnitude rise in resistivity values. The La-doped BaTiO3 ceramics co-doped with Mn gives an enhanced PTCR effect which can be exploited for various sensor applications.

The positive temperature coefficient of resistivity (PTCR) sensors is resistor materials that undergo a sharp change in resistivity at a designed Curie temperature due to its unique structure and chemical composition. This effect serves important control functions in a wide variety of electronic circuitry and similar applications. Conventional calcining of mixed oxides method (CMO) is used for fabricating lanthanum doped barium titanate (BaTiO3) for PTCR behaviour through solid-state-sintering route, at 1100°C, 1350°C. Two batches of samples were fabricated at low and high sintering temperatures of 1100°C, 1350°C respectively. The effect of different concentrations of donor dopant on BaTiO3 on the electrical properties of Ba(1-x)LaxTiO3 with x= 0.0005, 0.001, 0.002, 0.0025, 0.003 mol%, is investigated at low sintering temperature. The influence of lantanum doping with Al2O3+SiO2+TiO2 (AST) as sintering aids on the electrical properties of Ba(1-x)LaxTiO3 with x= 0.0005, 0.001, 0.003 mol%, is also investigated. The results of the electrical characterization for the first batch of samples showed an increase in room temperature resistance with increaisng donor concentration. Also the results of the electrical characterization for the second batch of samples also showed the same increase in room temperature resistance with increasing donor concentration. For first batch of sensors the high room temperature resistance keeps the jump small and these materials showed V-shaped NTCR-PTCR multifunctional cryogenic sensor behavior with a strong negative coefficient of resistance effect at room temperature.Where as the second batch of sensors showed few orders of magnitude rise in resistivity values. The La-doped BaTiO3 ceramics co-doped with Mn gives an enhanced PTCR effect which can be exploited for various sensor applications.