High-Performance Ceramics III

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Authors: Da Ming Cheng, Jing Feng Li
Abstract: Lead lanthanum zirconate titanate, PLZT ceramics have drawn great attention in microactuation because the Photostrictive Effect in it. In this study, compositional dependence of photostrictive effect in PLZT was investigated. The factual compositions were configurated quantitatively by XRF to characterize the deviation in the preparation process. Different sintering periods were designed in an attempt to obtain PLZT ceramics with the same grain size but different compositions to explore the intrinsic photostrictive effect in the PLZT system. With this method, the maximum intrinsic photocurrent was obtained at 3.48/50.7/49.3, while the maximum intrinsic photovoltage was obtained at 3.44/52.73/47.27.
Authors: Wen Gong, Xiang Cheng Chu, Jing Feng Li, Zhi Lun Gui, Long Tu Li
Abstract: Lead zirconate titanate (PZT) thin films with a composition near the morphotropic phase boundary were deposited on silicon wafers by using a modified sol-gel method. Introducing a seeding layer between the interface of PZT film and platinum electrode controlled the texture of PZT films. The lead oxide seeding layer results in highly (001)-textured PZT film, while the titanium dioxide seeding layer results in (111)-textured one. SEM and XRD were used to characterize the PZT thin films. The ferroelectric and piezoelectric properties of the PZT films were evaluated and discussed in association with different preferential orientations.
Authors: Jian Ling Zhao, Xiao Hui Wang, Long Tu Li
Abstract: (Ba,Sr)TiO3 films with thickness between 1 ~ 20 µm are fabricated by electrophoretic deposition using (Ba,Sr)TiO3 nanopowder synthesized by different methods including sol-gel, coprecipitation and conventional solid phase synthesis. Experiments show that conventional solid phase synthesis need higher crystallization temperature (>1000°C) and result in larger size of particle while in sol-gel and coprecipitation process (Ba,Sr)TiO3 crystallizes at lower temperature and results in smaller size of particle . Powders synthesized from various routes have different surface property. Deposition parameter must be adjusted accordingly to obtain dense and smooth (Ba,Sr)TiO3 film.
Authors: Zi Ping Cao, Ai Li Ding, Xi Yun He, Y. Zhang, X. Zeng
Abstract: Bi3.5Nd0.5Ti3O12 (BNT) ferroelectrics modified with different concentrations of Nb are prepared by a hot-pressing method. XRD diffraction shows that all samples have only a layeredstructured pervoskite phase. Raman spectra confirm that the crystal symmetry change locally when increasing Nb concentration. It is found that the introduction of a suitable amount of Nb can enhance the remnant polarization of BNT. The temperature dependence of dielectric constant is also investigated in BNT ceramics. All samples have high Curie temperature above 530°C.
Authors: Su Chuan Zhao, Lina Zhang, Guo Rong Li, Liao Ying Zheng, Ai Li Ding
Abstract: Na0.42K0.08Bi0.5TiO3 and Na0.45K0.05Bi0.5TiO3 ceramics were fabricated by the solid-state reaction. The structures were determined by X-ray diffraction. Dielectric, ferroelectric and piezoelectric properties of the ceramics were measured and discussed. The ceramics have a single perovskite phase with rhombohedral symmetry at room temperature. The thermal variations of the permittivity follow the law 1/ e − 1/ em = C(T − Tm)2 which is the character of typical relax ferroelectrics, when temperature is higher than the temperature of the maximum of dielectric constant (Tm). The depolarization temperature (Td) of spontaneous polarization is 215oC for Na0.45K0.05Bi0.5TiO3 and 152oC for Na0.42K0.08Bi0.5TiO3 respectively. There exist two different dielectric behaviors of the Na0.42K0.08Bi0.5TiO3 ceramic, without and after poling. Na0.45K0.05Bi0.5TiO3 possesses relatively high kt and Td. The use for device application has been indicated.
Authors: Lina Zhang, Guo Rong Li, Su Chuan Zhao, Liao Ying Zheng, Qing Rui Yin
Abstract: A mixed bismuth layer-structured compound, Bi7Ti4NbO21, has been prepared by the conventional solid state reaction. It showed an orthorhombic symmetry with a = 5.4428, b = 5.4043 and c = 29.041 Å by X-ray powder diffraction analysis. The hysteresis loops as a function of temperature were observed with a standardized ferroelectric test system. The remanent polarization and the coercive field of the material at 140°C were 14.06 µC/cm2 and 78.6 kV/cm, respectively. Thermal dependence of dielectric permittivity showed two-phase transitions at around 670°C and 845°C, which were also investigated by TSC and DSC. Finally, piezoelectric properties were obtained with a piezoelectric coefficient d33 = 10 pC/N. It was observed that Bi7Ti4NbO21 underwent a ferroelectric–paraelectric phase transition at 845°C by depolarization experiments.
Authors: Lina Zhang, Su Chuan Zhao, Liao Ying Zheng, Guo Rong Li, Qing Rui Yin
Abstract: A study was conducted on the effects of donor dopants, Nb2O5 and WO3, on microstructure and electric properties of Bi4Ti3O12 (BIT) ceramics. X-ray diffraction patterns of the materials showed a single orthorhombic phase structure. The microstructure results revealed the appearance of plate-like grain. The donor doping decreased the conductivity of BIT by as much as 3 orders of magnitude. The dielectric and ferroelectric properties of doped-BIT materials were also investigated. The decrease in the electrical conductivity allowed the doped samples to be poled to develop piezoelectricity. Thermal annealing studies of the samples indicated the donor-doped BIT were suitable candidate materials for high-temperature piezoelectric applications.
Authors: Liao Ying Zheng, Guo Rong Li, Wang Zhong Zhang, Qing Rui Yin
Abstract: In this paper, the bismuth-layered structure piezoelectric ceramics (Ca,Sr)Bi4Ti4O15 doped with CeO2 are prepared by the solid state reaction method. The crystal structure of the ceramics is determined by X-ray diffraction and the single orthorhombic structure phase is found. However, the doping of CeO2 increase the lattice parameters a, b, c. As a result, the ions of Ce enter into the lattice of the bismuth-layered structure and occupy A sites in the perovskite layer of bismuthlayered structure lattice. The temperature dependence of the conductivity shows that the resistivity increases by doping of CeO2 and reaches its maximum when the doping content is 0.4mol%. The mechanism of the CeO2 doping is also analyzed. By the investigation of XPS, the Ce ions have two types of valences: Ce3+ and Ce4+. The existence of Ce ions strengthened the weak Bi-O bonding and decreased the oxygen vacancies in the lattice, so the ceramics have lower conductivity.
Authors: Shao Ze Yan, Fu Xing Zhang, Yang Min Li
Abstract: Piezoelectric materials have an ability to efficiently transform mechanical energy to electric energy and vice versa, which makes them useful as structural dampers. The objective of this work is to investigate the damping capabilities of a piezoceramic shunted by different types of passive electrical circuits. The material properties of the shunted piezoceramic are modeled and the analytical results show that the shunted piezoceramic exhibits different damping potentials depending on the piezoelectric properties of the material and the shunt circuits. An experimental set-up of a cantilever beam with surface bonded piezoceramics is proposed to investigate the damping characteristics of the shunted piezoceramic. An analytical model is developed to describe the influence of the shunted piezoceramic on the dynamic response of the beam. The damping performances of the piezoceramic shunted by different circuits are compared respectively and the experimental results show approximate agreement with the numerical simulations of the model.
Authors: Guo Zhong Zang, Jin Feng Wang, Hong Cun Chen, Wen Bin Su, Chun Ming Wang, Peng Qi, Bao Quan Ming
Abstract: The effect of Gd2O3 on the electrical properties of (Co, Nb)-doped SnO2 varistors was investigated. It was found that the nonlinear coefficient presents a peak of α = 30 for the sample doped with 1.5mol% Gd2O3. The increase of the breakdown electrical field from 325V/mm to 1560V/mm with increasing Gd2O3 concentration is mainly attributed to the decrease of the grain size. The decrease of relative density and resistance of grain boundary indicate that Gd2O3 should be a two-sided dopant and the nonlinear coefficient peak was explained. To illustrate the grain-boundary barrier formation of (Gd, Co, Nb) doped SnO2 varistors, a modified defect barrier model was introduced, in which the negatively charged acceptors substituting for Sn ions should not be located at the grain interfaces instead at SnO2 lattice sites of depletion layers.

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