High-Performance Ceramics III

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Authors: Cheng Ju Zhang, Jin Feng Wang, Wen Bin Su, Guo Zhong Zang, Hong Cun Chen
Abstract: The effects of Pr on the microstructure and nonlinear electrical properties of the (Co,Ta)-doped SnO2 varistors were investigated. It was found by characterizing the samples sintered at 1350 oC that the breakdown voltage increases significantly from 500v/mm to 1200v/mm, and the relative permittivity decreased rapidly from 2525 to 1199 with increasing Pr6O11 concentration from 0 to 1.20 mol%. The analysis of samples’ microscopic structure showed that the grain size of SnO2 rapidly decreases from 5.1 to 3.7 µm with increasing Pr6O11 concentration from 0 to 1.20mol% .The significant decrease of SnO2 grain size is the main reason for raising breakdown voltage and reducing permittivity.
275
Authors: Yong Qing Wang, Jian Qing Wu, Jianer Zhou
Abstract: Antistatic ceramic tiles was prepared by adding 15wt% or more synthesized Sb-doped SnO2 into their glazes. The tiles have the surface resistivity ρs of 1.40 × 106 to 5 × 108 Ω×cm. The conduction mechanism was analyzed and it was shown that the electrostatic charges are eliminated by the network formed by the Sb-doped SnO2 distributed in the glaze.
279
Authors: Wei Chang Hao, Jun Ying Zhang, Hai Bing Feng, Tian Min Wang
Abstract: Quantum size ZnO colloids were prepared by sol-gel method and size of colloids together with the luminescence properties were changed by varying preparing time and temperature. The absorption onset and the maximum of fluorescence peak of the ZnO colloid have obvious shift in UV region and visible light region respectively. The relationship between luminescence properties and energy level splitting is discussed in detail based on the experimental results.
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Authors: Zhen Ya Lu, Zhi Wu Chen, Feng Jin Yang
Abstract: The voltage response of ZnO varistors to 8/20 µs surge current was investigated. The observed frontal spikes on the residual voltage waveforms are caused by the ignition gap, and no frontal spike was observed when a thyristor was used as the discharge trigger. The rear part of the waveform is determined by the damping coefficient of the RLC-circuit. Near the critical point, the residual voltage waveform changes from non-oscillating attenuation modes to distinct across zero oscillating modes along with the increase of the peak current, but there will be no oscillation happen when a thyristor is used as the discharge trigger. The residual voltage peak is not synchronized with the current peak, and the voltage peak is leading, implying that the ZnO varistor appears to be inductive. According to the experiment results, it can be reasonably explained that the voltage peak leading phenomenon is attributed to the transient skin effect of the varistor materials.
285
Authors: Wen Bin Su, Jin Feng Wang, Hong Cun Chen, Guo Zhong Zang, Peng Qi, Chun Ming Wang
Abstract: The nonlinear electrical properties of TiO2-based varistor doped with 0.25mol% Ta2O5 and different contents of Sc2O3 were investigated. It was found that the TiO2 varistor ceramic doped with 0.10mol% Sc2O3 exhibited an optimal nonlinear coefficient of 7.8, a breakdown electrical field of 16.0V/mm, and relative dielectric constant of 1.27 × 105 (measured at 1 kHz). In order to analyze the effect of Sc2O3 on TiO2 varistors, studies were made on the capacitance versus voltage characteristics. A Schottky-type barrier, which is assumed as the origin of varistor behavior, was inferred from the C-V measurement. The barrier height and donor concentration were obtained as 0.41eV and 1.21 × 1026cm-3, respectively, for sample doped with 0.10mol% Sc2O3. Analogized to the ZnO varistors, the formation mechanism of Schottky-type barrier was discussed in this paper by the theory of defect in crystal lattice.
289
Authors: Feng Pan, Jun Ying Zhang, Hai Ying Liu, Tian Min Wang, Wei Chang Hao
Abstract: Ag nano-particles were deposited on the surface of TiO2 self-assembled films by photo-reduction of Ag+ solution. SPM, XPS and UV-Vis spectrophotometer were employed to characterize the microstructure and photo-catalytic performance of the films. An obvious enhancement of photo-catalytic activity had been observed. Since rutile had a lower optical band gap than anatase, a higher photo-catalytic efficiency improvement of rutile than that of anatase was obtained under the help of Ag nano-particles, which acted as electron acceptors.
293
Authors: Shao Hua Luo, Zi Long Tang, Hong Yun Li, Zhong Tai Zhang, Xi Zhou Xiong
Abstract: The present work attempted to investigate the effect of Nb addition on the electrical properties of the (Ca,Si,Ce,Nb)-doped TiO2 ceramics. The content of added niobium is in the range 0.1-1.0mol %, while that of the other additives keeps constant. The results showed that an optimal composition doped with 0.8mol% Nb2O5, followed by sintering at 1350°C, was obtained with low V1 mA of 7.22V, high nonlinear coefficient of 5.76, ultrahigh dielectric constant (er = 86000) as well as relatively low loss (tgd = 0.52) in room temperature at 1 kHz. SEM studies show that change of niobium had significant influence on grain growth and micro structural characteristics of the sintered samples.
297
Authors: Jia Mi, Zi Long Tang, Shao Hua Luo, Zhong Tai Zhang
Abstract: The influence of La2O3 and CeO2 on a new class of polystalline ceramics with electrical properties based on TiO2 was investigated. The content of added La and Ce is in 1 at%, while that of the other addition is always maintained at a constant value. The disks were sintered at 13800C for 4 hours. La2O3 was found to precipitate at the grain boundaries, probably inducing electronic interface states that can trap charges at the TiO2-TiO2 interface and lead to significantly increase the nonlinear behavior. The values for α (» 4.2) and V1mA(» 26 V) support that finding. It was found CeO2 that as a dopant did not strongly influence the nonlinear values of the systems as did La2O3, indicating that it could have formed a solid-state solution with TiO2 in the grains, but did not segregate sufficiently at the grain boundaries. In present work, impedance analyzer, X-ray spectrometer, and scanning electron microscope (SEM) were used.
301
Authors: Tao Yan, Xiao Lin Liu, Jian Feng Chen
Abstract: The sensitivity of CuO dispersed on fluorite-type oxide, namely CeO2 was studied in this work. Mixed oxide sample of nanostructured CuxCe1-xO2-y of various composition were generated by step chemical precipitation method. Distinct copper species were identified as a function of copper content by X-ray photoelectron spectroscopy, X-ray powder diffraction, the special surface areas, transmission electron microscopy, scanning electron microscopy analysis, and sensing properties to CO. It was found that only small amounts of copper are sufficient to promote the sensitivity of CeO2 by several orders of magnitude, which excessive amounts of copper (Cu/(Cu+Ce)>0.12) are detrimental to the sensing properties of nanocompositions. The possible causes for this behavior are also discussed.
305
Authors: Yan Fei Gu, Hui Ming Ji, Bin Zhang, Ting Xian Xu
Abstract: CuO-SrTiO3-based thin films were prepared by novel sol-gel technology on Al2O3 substrates using Cu(NO3)2, SrCl2 and TiCl4 as the starting materials, critic acid and ethylene glycol as chelating agents. CO2 sensing properties of the films were investigated. Structure characteristics of the sol and asgrown thin films were analyzed by FT-IR spectrum, X-ray diffraction and SEM. The results reveal that the films consisted of CuO phase and SrTiO3 phase have nanocrystalline microstructure at 750°C for 40 min. The modified CuO-SrTiO3 thin films exhibit good resistance-temperature and gas sensitivity properties in a wide range of temperature. The films exposed to 6% CO2 show that sensitivity are 32, and response and recover time are within 2 s at 250 °C operating temperature.
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