High-Performance Ceramics IV

Paper Title Page

Authors: Hong Jie Zhao, Ji Zhou, Zhi Lun Gui, Long Tu Li
Abstract: The effects of Bi-substitution on the complex impedance spectra of yttrium iron garnet (YIG) were studied in this paper. The polycrystalline yttrium iron garnet Y2BiFe5O12 (YIG: Bi) and Y3Fe5O12 (YIG) samples were prepared by solid-reaction method. The complex impedance spectra were measured in the frequency range from 1 KHz to 100MHz at several temperatures between 210oC and 500oC. The complex impedance sample shows that the YIG: Bi can be represented by double Cole-Cole semicircles, and the YIG can be represented by a single Cole semicircle. The physical structure of the specimen was visualized as comprising of small resistance grains separated by large resistance grain boundaries in accordance with the impedance spectra observations. The electrical processes in the sample were modeled in the form of an electrical equivalent circuit made up of a series combination of two parallel RC circuits attributed to grains and grain boundaries. The temperature dependence of bulk resistance indicated an evidence of Arrhenius-type thermally activated process, showing a close to linear variation up to a temperature of 740 K.
Authors: Y. Chen, Dong Ying Ju
Abstract: Because of the raw material elements and its purity and so on, the Nd-Fe-B permanent magnet, the strongest magnetic material, which needs artificial synthesis, can hardly be used directly. The performance of the permanent magnet has not yet been greatly developed owing to the limitation of the artificial synthesizing technology, of the powder sintering technology and that of the application. In this paper, the magnetic abrasive machining method as a new application is put forward, and from this viewpoint, are discussed the performance and the processing technology of the permanent magnet and the magnetic abrasive machining method. A sintering route combining the direction heat treatment technique to increase the magnetic energy is suggested.
Authors: Jun Ki Chung, Won Jeong Kim, Sung Gap Lee, Cheol Jin Kim
Abstract: Superconducting YBa2Cu3O7-δ(YBCO) films were grown on MgO single crystalline substrates using a BaZrO3 (BZO) buffer layer deposited by a pulsed laser deposition (PLD). Deposition condition has been optimized to obtain good epitaxial BZO film followed by deposition of YBCO superconducting films. The crystallinity and microstructure of epitaxial YBCO/ BZO/ MgO (00l) films were investigated by a two-dimensional x-ray diffraction and a field emission scanning electron microscope. The in-plane (φ-scan) measurements for the BZO films (200 ~ 500 nm thick) grown on MgO substrates revealed a narrow full width half maximum (0φ = 2o). The XRD results exhibited that YBCO films with a BZO buffer layer were well oriented in the [00l] direction perpendicular to the substrate surface. The BZO films also showed homogeneous and dense surface morphologies. By the deposition of a subsequent BZO buffer layer, YBCO was grown epitaxially on MgO with results showing a critical current density (Jc) of ~ 3.3 × 106 A/cm2 and a critical temperature (Tc) of 86 K.
Authors: Ming Ya Li, Xi Wei Qi, Zhi Yong Yu, Zheng He Han
Abstract: The stability range of lead oxide compounds Pb3Sr2.5Bi0.5Ca2CuOy (3321) phase in Bi-system high temperature superconducting materials has been investigated. In this study (Bi,Pb)2Sr2Ca2Cu3Ox (BSCCO) powder was heat treated in different oxygen partial pressure and different temperature. The formation and the relative volume fraction of the 3321 phase were determined by X-ray diffraction. The microstructure of the quenched pellets was observed using SEM. Experimental results show that the stability range of the 3321 phase depends on both the temperature and oxygen partial pressure. A three dimensional plot of relative 3321 phase formation was obtained for BSCCO powder in which the main phase is (Bi,Pb)-2212 at different temperature and oxygen partial pressure.
Authors: Metin Gürü, Yüksel Akyüz, Süleyman Tekeli
Abstract: The discovery of superconductivity at 39 K in magnesium diboride (MgB2) has attracted much attention from theoretical and experimental points of view because it has the highest superconducting transition temperature in the conventional intermetallic superconductors reported so far. After the discovery of superconductivity in MgB2, many attempts have been made to synthesize this material with an aim of improving superconducting properties. In this study, MgB2 was synthesized from anhydrous B2O3. To provide homogeneous mixing of magnesium and boron oxide powders and to make easy sintering, powders were mechanically milled in an attritor under argon gas atmosphere. The mixture was treated with ethylenediamine solution to separete MgB2 from the product. The suspension solution was filtrated under vacuum and the solid particulates of MgO were removed. The filtrate was evaporated in a vacuum oven at 80 °C and sintered at 900 °C for 2 h under flowing argon gas atmosphere. XRD results showed that the final product was MgB2 with a small amount of MgO. Mechanical milling decreased the synthesis time and temperature of MgB2. The critical temperature of the specimens was determined as 37.4 K by an A.C susceptometer.
Authors: Yao Hui Xue, Chang Sheng Deng, Quing Feng Li, De Sheng Ai, Xia Ming Dai
Authors: Hiroshi Masumoto, Akihiko Ito, Y. Kaneko, Takashi Goto
Abstract: BaRuO3(BRO) and BaIrO3(BIO) thin films were prepared by laser ablation, and the effects of preparation conditions on the structure, morphology and electrical conductivity were investigated. BRO thin films deposited at oxygen partial pressure (PO2) = 13 Pa and substrate temperature (Tsub) < 573 K were amorphous. At Tsub = 573 K, the rhombohedral BRO thin films with (110) orientation were obtained. BRO thin films prepared at Tsub = 773 K and PO2= 13 Pa exhibited the resistivity of 5x10-6 m and showed metallic conduction. BIO thin films deposited at PO2= 40 Pa and Tsub < 623 K were amorphous. Tsub > 623 K, the BIO thin films crystallized into a 6H structure were obtained. The resistivity of the BIO films at PO2= 40 Pa decreased from 1.4x10-2 to 4x10-4 m with decreasing Tsub from 1073 to 573 K.
Authors: Ming Zhao, Wei Min Wang, Xiang Chun Liu, Chang Sheng Tian
Abstract: The effects of pre-synthesized V2O5/Sb2O3 compound, SbVO4 and Sb2O3 on the microstructure and electrical properties of ZnO-V2O5 based varistor ceramics have been studied. The general homogeneous microstructure and phase composition of the ceramics have not been influenced by the antimony doping form changes, except for the gradual decrease in average grain size and the increase in spinel formation within the ceramics. The ultimate cause of micro-structural variations with the antimony doping form changes seems to have been the gradual increase in Sb3+ concentration within the ceramics. This change in micro-composition, together with the changes in microstructure, caused the electrical characteristics of the ceramics to vary. The pre-synthesized V2O5/Sb2O3 compound is the most effective antimony dopant in term of its effect on the ceramics.
Authors: Lan Yi Wang, Cheng Xiang Lu, Guo Yi Tang
Abstract: Two types of multilayer ZnO varistors are prepared by the chemically synthesized (CS) powder and the mixed oxide (MO) powder. The ceramic microstructure analysis shows that the multilayer variestor (MLV) ceramic prepared by the CS powder has the fine grain, the homogeneous distribution of grain size and the uniform dopant distribution. The CS powder prepared multilayer ZnO varistors display better electrical properties, including higher nonlinear coefficient, higher breakdown voltage, higher peak current, lower leakage current and lower clamping voltage, than those made by the mixed oxide powder. All these superior electrical properties are attributed to the CS powder, which makes more uniform dopant distribution throughout the multilayer ZnO varistors. The homogeneous distribution for the various dopants in the varistor ceramic has been achieved by the chemically synthesized doped ZnO powder. Therefore, the chemically synthesized powder can be used in the manufacture of high performance multilayer ZnO varistors.
Authors: Wei Min Wang, Xiang Chun Liu, Ming Zhao, Chang Sheng Tian
Abstract: The aim of this paper is to investigate the effects of V2O5 additive on the electrical properties of NTC thermistors based on Ni0.5Co0.5Mn2O4.The XRD analyses indicate that single spinel phase can form, and V2+ions are in the octahedral interspace. The cell can be enlarged due to the V2O5 additive. The resistivities (ρ) and the material constant (B) increase obviously, the reasons of which are mainly attributed to the outer electron configuration of V2+ and cell enlargement.

Showing 201 to 210 of 766 Paper Titles