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Key engineering materials
Trans Tech Publications Ltd.
Key engineering materials

Trans Tech Publications Ltd.

半月刊

1013-9826

Key engineering materials/Journal Key engineering materials
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    Control of the Shrinkage during Hybrid Microwave Sintering of Nano-Sized ZnO Based Powder for Varistors

    Sylvain MarinelEtienne SavaryAlain PautratRichard Retoux...
    376-381页
    查看更多>>摘要：The microwave heating allows sintering in a very short time which is useful to keep the materials nanostructure. Up to now the trial error method is commonly used to find the best experimental parameters. This method is time consuming and does not allow getting a high reliability. In this work, a specific optical based position sensing device has been used to record the shrinkage during hybrid microwave sintering. Owing to this particular device, the control of the nano-sized ZnO based powder sintering has been successfully achieved. Very fine microstructures were obtained and electrical properties of those nano-ceramics were determined.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Admittance Spectroscopy of Y_2O_3-doped ZnO Varistors Sintered at Different Temperature

    Jun LiuJinliang HeJun HuWangchen Long...
    382-385页
    查看更多>>摘要：ZnO varistors are multicomponent polycrystalline ceramics with highly nonlinear current-voltage characteristics and surge energy absorption capabilities. The voltage gradient of the ZnO varistor is inversely proportional to its average grain size. Recently, the rare-earth oxides have been reported as growth inhibitor of ZnO grains to obtain high voltage gradient. Although the dopant of rare-earth oxides can remarkably enhance the voltage gradients of varistor samples, their leakage currents and nonlinear coefficients deteriorate at the same time. In this paper, the sintering effects on electrical characteristics and admittance spectroscopies of ZnO varistor samples doped with yttrium oxides were investigated. Samples were fabricated under different sintering temperatures, including 1000℃, 1100℃, 1200℃ and 1300℃. Then, the electrical characteristics and admittance spectroscopies of these varistor samples were measured. The measured current-voltage results behave special U-type curves related to sintering temperature. Furthermore, the admittance spectroscopy of these samples revealed the sintering effects on the intrinsic defects of ZnO varistors.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Origin of Leakage Currents in ZnO Based Varistor Ceramics with Al(NO_3)_3 Dopant

    Jun HuWangcheng LongJinliang HeJun Liu...
    386-388页
    查看更多>>摘要：The additive of Al(NO_3)_3 has been doped into ZnO varistors in order to reduce their residual voltages. However, the leakage currents of samples always increase at the same time. Generally, it is recognized that some of doped Al~(3+) ions enter the ZnO grains and reduce their resistivity, which results in lower residual voltages of varistor samples. On the other hand, the remnant Al~(3+) ions appear in the grain boundaries and also reduce their resistivity, which results in larger leakage currents. In this paper, the electrical properties of ZnO varistor samples with various amounts of Al(NO_3)_3 dopant were measured. The experimental data are compared with the numerical simulation results, which reveals that the increased leakage currents of ZnO varistors with Al(NO_3)_3 dopant are not only due to the decreased resistivity of grain boundaries, but also the increased donor density of ZnO grains.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    ZnO-Pr_6O_(11)-Co_3O_4-TiO_2-based Ceramic Varistor Materials

    Hai FengZhijian PengChengbiao WangZhiqiang Fu...
    389-392页
    查看更多>>摘要：The preparation and characterization of ZnO-Pr_6O_(11)-Co_3O_4-TiO_2 (ZPCT) based varistor materials with different doping levels of TiO_2 and Pr_6O_(11) were investigated. The results reveal that: (1) TiO_2 is an important additive, acting as an inhibitor of ZnO grain growth. The doping of appropriate amount of TiO_2 can significantly improve the nonlinear properties and decreases the leakage current of the varistors, achieving a relatively high nonlinear exponent and low leakage current with 1.0 mol% TiO_2 doped. (2) The oxide of Pr_6O_(11) microstructurally plays the role of inhibition in grain growth. The doping of appropriate amount of Pr_6O_(11 can improve the nonlinear property, and decrease the leakage currents of the varistors, acquiring the optimum results with 1.5 mol% Pr_6O_(11) doped.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Rapid Synthesis of Bi Substituted Ca_3Co_4O_9 by a Polyacrylamide Gel Method and Its High-temperature Thermoelectric Power Factor

    Ying SongQiu SunLirong ZhaoFuping Wang...
    393-396页
    查看更多>>摘要：A series of polycrystalline (Ca_(1-x)Bi_x)_3Co_4O_9 ( x = 0.0 ～ 0.075 ) powders were synthesized rapidly by a polyacrylamide gel method. The dense ceramics were fabricated using the spark plasma sintering ( SPS ) technique. Effects of Bi substitution on high temperature thermoelectric properties of Ca_3Co_4O_9 were evaluated. Both the electrical conductivity and Seebeck coefficient increased with increasing Bi content up to x = 0.05, thus leading to an enhanced thermoelectric power factor. The Bi substituted sample with x = 0.05 obtained in this study has the highest thermoelectric power factor in the measured temperature range. It reaches 4.8×10~(-4) Wm~(-1)K~(-2) at 700 ℃, which is 26 % higher than that ofCa_3Co_4O_9 without Bi substitution, and is by up to 15 % larger as compared to the Bi substituted sample synthesized by the solid state reaction method and the SPS technique due to the high chemical homogeneous powder prepared by the polyacrylamide gel method.
      原文链接:
    • NETL
    • NSTL

    Effects of pH Value on the Structures and Optical Properties of Bi_2S_3 Thin Films

    Huang Jian-FengWang YanCao Li-YunZhu Hui...
    397-399页
    查看更多>>摘要：Bismuth sulfide (Bi_2S_3) is an important semiconductor material, which has wide applications in thermoelectricity, electronics, photoelectricity and infrared spectroscopy. Bi_2S_3 thin films have been deposited on ITO substrates through a cathodic electrodeposition approach at room temperature. The as-deposited thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence spectrum (PL). The effects of solution pH values on the structures and optical properties of the thin films were particularly investigated. Results show that uniform Bi_2S_3 thin films with oriented growth along (240) direction can be obtained at the solution pH value range from 4.5 to 6.5. The as-prepared thin films exhibit stable blue-green photoluminescence properties under the ultraviolet light excitation at room temperature. With the increase of the solution pH values, the crystallization of the Bi_2S_3 thin films improves while the grain size of the obtained thin films decreases and the light emission intensity of the thin films decreases.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Synthesis and Thermoelectric Properties of Ca_2CO_2O_5 Ceramics

    Zhao ShujinLi GuojingZhang YangMei Ao...
    400-403页
    查看更多>>摘要：The precursor of Ca_2CO_2O_5 was prepared by coprecipitation method. The bulk Ca_2CO_2O_5 samples were prepared by conventional sintering and Spark Plasma Sintering (SPS), respectively. The relative density of bulk Ca_2CO_2O_5 ceramic, which was prepared by conventional sintering is about 75%; while the samples prepared by SPS has a density of 98%. The thermoelectric properties were enhanced by SPS, compared with samples prepared with conventional sintering. The maximum powerfactor of the conventional sintering and SPS samples are 2.70×10~(-4) W·m~(-1)·K~(-2) and 3.85×10~(-4) W·m~(-1)·K~(-2), respectively.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Preparation and Thermoelectric Properties of LaCoO_3 Ceramics

    Li FuJing-Feng Li
    404-408页
    查看更多>>摘要：LaCoO_3 ceramics were prepared by conventional solid state reaction and normal sintering at the temperatures ranging from 1373 to 1523 K. The sintered densities increased with increasing sintering temperature and exceeded 90 % of the theoretical values when sintered above 1473 K. The thermoelectric properties of the samples sintered at different temperatures were investigated from 323 to 673 K. The LaCoO_3 samples showed a negative Seebeck coefficient, whose absolute values decreased dramatically with increasing temperature in the range of 323 to 460 K, then changed to a positive value and lightly decreased above 460 K. The electrical conductivity increased with increasing temperature, indicating a semiconducting behavior. The Seebeck coefficients showed little difference between the samples sintered at different temperatures, but the power factor of the sample sintered at a higher temperature was larger because of the higher electrical conductivity.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Effect of Mn_2O_3 Addition on the Electric and Physical Properties of Lead-Free 0.98(Na_(0.5)Bi_(0.5))TiO_3-0.02 Ba(Sn_(0.08)Ti_(0.92))O_3 Piezoelectric Ceramics

    Chun-Huy Wang
    409-412页
    查看更多>>摘要：In this paper, the effect of Mn_2O_3 additions on the electrical and physical properties of 0.98(Na_(0.5)Bi_(0.5))TiO_3 -0.02Ba(Sn_(0.08)Ti_(0.92))O_3 was investigated. X-ray diffraction analysis revealed that, during sintering, all of the Ba(Sn,Ti)O_3 diffuse into the lattice of (Na_(0.5)Bi_(0.5))TiO_3 to form a solid solution, in which a hexagonal phase with a perovskite structure was found. The 0.98(Na_(0.5)Bi_(0.5))TiO_3 -0.02Ba(Sn_(0.08)Ti_(0.92))O_3 [0.98NBT-0.02BST] ceramics with the addition of 0～4.0 wt% Mn_2O_3 have been prepared following the conventional mixed oxide process. For 0.98NBT-0.02BST ceramics by doping 1.0 wt% Mn_2O_3, the electromechanical coupling coefficients of the planar mode k_p and the thickness mode k_t reach 0.12 and 0.52, respectively, at the sintering of 1100℃ for 3 h. The 0.98NBT-0.02BST ceramic with 1 wt% Mn_2O_3 addition exhibit a more homogeneous and grain size of～3.5 urn. With suitable Mn_2O_3 doping, a dense microstructure and good piezoelectric properties were obtained.
      原文链接:
    • NETL
    • NSTL

    Effect of Bi_2O_3 Addition on the Electrical and Physical Properties of Lead-Free 0.98(Na_(0.5)K_(0.5))NbO_3-0.02 Ba(Zr_(0.04)Ti_(0.96))O_3 Piezoelectric Ceramics

    Chun-Huy Wang
    413-416页
    查看更多>>摘要：The 0.98(Na_(0.5)K_(0.5))NbO_3-0.02Ba(Zr_(0.04)Ti_(0.96))O_3 ceramics have been prepared following the conventional mixed oxide process. X-ray diffraction analysis revealed that, during sintering, all of the Ba(Zr_(0.04)Ti_(0.96))O_3 diffuses into the lattice of (Na_(0.5)K_(0.5))NbO_3 to form a solid solution, in which a orthorhombic phase with a perovskite structure was found In order to improve the sinterability of the ceramics, Bi_2O_3 additions were used as a sintering aid. The electromechanical coupling coefficients of the planar mode k_p and the thickness mode k_t reach 0.3 and 0.55, respectively, at the sintering of 1100℃ for 5 h. For 0.98NKN-0.02BZT ceramics by doping 0.5 wt.% Bi_2O_3, the electromechanical coupling coefficients of the planar mode k_p and the thickness mode k_t reach 0.21 and 0.57, respectively. The ratio of thickness coupling coefficient to planar coupling coefficient is 2.7.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd