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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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    Preparation of Barium Titanate Grain-oriented Ceramics and Their Piezoelectric Properties

    Rintaro MoriPetr PulpanHiroshi HayashiYoshitaka Nagamori...
    P.3-6页
    查看更多>>摘要：Barium titanate (BaTiO_3, BT) grain-oriented ceramics along [110] direction were prepared by a templated grain growth (TGG) method. The [110] oriented BT platelike particles (t-BT) were used as template particles. BT grain-oriented ceramics with higher relative density (D_(rel)) over 95 %, high degree of orientation along [110] direction (F_(110)) over 80 % and grain sizes around 30 urn were successfully prepared using only the template particles. The relationship between microstructures and piezoelectric constant (d_(33)) was investigated. The higher F_(110) was, the higher D_(rel) and the smaller grain size were required for enhancement of the piezoelectric properties.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Crystal growth and ferroelectric properties in Bi_(0.5)K_(0.5)TiO_3-Bi_(0.5)Na_(0.5)TiO_3 crystals

    Akifumi MorishitaYuuki KitanakaMakoto IzumiYuji Noguchi...
    P.7-10页
    查看更多>>摘要：Single crystals of x (Bi_(0.5)K_(0.5))TiO_3-(1-x)(Bi_(0.5)Na_(0.5))TiO_3 (BKT-BNT) solid solution were grown by a flux method, and their ferroelectric properties were investigated along [100]_(cubic) (the cubic notation). While the flux growth soaked at 1250 ℃ led to the crystals with a composition of x less than 0.14, the crystals with x of 0.45 were obtained by decreasing soaking temperature to 1150 ℃. The crystals of BKT-BNT (x = 0.45) exhibited a relatively large remanent polarization of 39 μC/cm~2 and a low coercive field of 23 kV/cm.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Enhanced Piezoelectric Properties of Barium Titanate-Potassium Niobate Solid Solution System Ceramics by MPB Engineering

    Shigehito ShimizuPetr PulpanNobuhiro KumadaDaisuke Tanaka...
    P.11-14页
    查看更多>>摘要：Barium titanate (BaTiO_3, BT) - potassium niobate (KNbO_3, KN) solid solution system (0.5BT-0.5KN) ceramics with various microstructures were prepared by conventional sintering method and two-step sintering method using BT and KN nanoparticles. Their microstructures were investigated using X-ray diffraction (XRD) measurement and scanning electron microscopy (SEM), and it was confirmed that two ferroelectric phases, i.e., BT-rich tetragonal and KN-rich orthorhombic phases, always coexisted for all ceramics, which suggested that 0.5BT-0.5KN ceramics had "pseudo-morphotropic phase boundary (MPB)" structure. Thus, the control of the interface area between two phases was important to enhance piezoelectric property. Finally, their piezoelectric property was measured, and the apparent piezoelectric constant d_(33)~* increased with increasing interface area.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Fabrication and Microstructure of Grain-Oriented (Bi_(1/2)K_(1/2))TiO_3 Ceramics

    Masahiro SaitohYuji HirumaHajime NagataTadashi Takenaka...
    P.15-18页
    查看更多>>摘要：Grain-oriented (Bi_(1/2)K_(1/2))TiO_3 (BKT) ceramics were prepared by the reactive templated grain growth (RTGG) method, and a hot-pressing (HP) method was modified on the basis of the RTGG method to obtain dense ceramics. The BKT ceramic sintered at 1060℃ showed a single-phase perovskite structure. The grain-oriented BKT prepared by the HP method exhibited a relatively high orientation factor F of 0.82 and a high density ratio of 99%. SEM micrographs of the HP-grain-oriented BKT indicated a textured and poreless microstructure. On the basis of the density ratio of 87% for the grain-oriented BKT without HP, the HP method was considered very effective for improving the density ratio even for the RTGG sample. In addition, the resistivity of the HP-grain-oriented BKT was 1.73 × 10~(13) Ω·cm.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Effect of Al_2O_3 Additives in PZT-Pb(Mn_(1/3)Nb_(2/3))O_3 ceramics

    Keisuke TeranishiTomohisa AzumaMasakazu Hirose
    P.19-22页
    查看更多>>摘要：The effect of adding Al_2O_3 to the PZT-PMN solid solution material for use for ceramic resonator was investigated. It has been found that when the amount of Al_2O_3 added to PZT-PMN is 0.3 wt% or below, it exists inside the crystal lattice as Al~(3+) ion and increases the stability of oscillation frequency over application of heat (heat resistance). It has been found that when more than 0.3 wt% of Al_2O_3 is added, the Al~(3+) ion that remained undoped will exist at grain boundary as secondary phase, and increase the strength.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Crystal Structure Analysis of High T_C Barium Titanate - Bismuth Perovskite-type Oxide System Ceramics and Their Piezoelectric Property

    Keisuke YamatoNobuhiro KumadaPetr PulpanSatoshi Ohno...
    P.23-26页
    查看更多>>摘要：Barium titanate (BaTiO_3, BT) - bismuth titanate magnesium oxide (Bi(Mg_(0.5)Ti_(0.5))O_3, BMT) solid solution system ceramics were prepared by conventional sintering method in pursuit of the enhancement of the BT Curie temperature (T_C, 132 ℃). Normal ferroelectric polarization vs. electric-field (P-E) hysteresis loops were observed for BT-BMT ceramics with BMT contents below 20 and above 60 molar%. On the other hand, broad P-E double hysteresis loops were observed for BMT contents from 30 to 50 molar%. The origin was investigated using synchrotron XRD measurement and Rietveld analysis. The crystal structure was assigned to ferroelectric phase with domain-pinning by certain defect structures. A modified phase diagram was proposed on the basis of the temperature dependence of the crystal structure.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Dielectric Properties of Barium Titanate Ceramics with Nano-Sized Domain

    Yoichi KigoshiSaki HattaTakashi TeranishiTakuya Hoshina...
    P.27-30页
    查看更多>>摘要：Barium titanate (BaTiO_3) ceramics with various grain sizes from 0.7 to 13 μm on average were prepared by a conventional sintering method, a two-step sintering method and a rate controlled two-step sintering method. The permittivity of the ceramics was increased with decreasing grain size to 1.1 μm on average. However, the permittivity of the ceramics was decreased when the grain size was below 1 μm. The field emission scanning electron microscope (FE-SEM) observations revealed that the 90° domain width decreased with decreasing the grain size. By ultrawide range dielectric spectra from kHz to THz range of the BaTiO_3 ceramics, the domain contribution to the permittivity was investigated. For the BaTiO_3 ceramics with grain sizes over 1 μm, the dipole polarizability and the ionic polarizability were enhanced by high domain-wall density. In contrast, for the BaTiO_3 ceramics with grain sizes below 1 μm, these polarizabilities were weakened.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Evolution of Internal Stress and Influence on Dielectric Properties by Number of Dielectric Layers in MLCC

    Satoshi YokomizoTakuya HoshinaHiroaki TakedaKatsuya Taniguchi...
    P.31-34页
    查看更多>>摘要：We researched the phenomenon that the permittivity of dielectric layers in multilayer ceramic capacitor (MLCC) increases with the number of dielectric layers. Finite element method (FEM) shows that the internal residual stress in MLCC was generated by the difference of thermal expansion coefficient between internal electrodes and dielectric layers. We developed a electric measurement system with applying external stress for understanding the stress influence on dielectric properties. The compressive stress along electric field increased the polarization. The polar nano regions (PNRs) in shell composition dielectrics were easily influenced by stress. Based on these results, the relationship between the number of dielectric layers and their permittivity in MLCCs was explained.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Degradation of resistance over time for multilayer ceramic capacitors

    Koichiro MoritaYouichi MizunoHirokazu Chazono
    P.35-38页
    查看更多>>摘要：The lifetime determination model for multilayer ceramic capacitors (MLCCs) is discussed. The accumulation of oxygen vacancies on the cathode/ceramics interface by an electro-migration process is a concept accepted by many researchers. However, the lifetimes and leakage currents measured during a highly accelerated lifetime test (HALT) could not be explained by this concept. To investigate the mechanism, we used a polarity reversal method during the HALT, which provided information on the dominant process for the leakage current. Thermally stimulated current (TSC) measurement provided the relative number of oxygen vacancies both on the cathode/ceramics interfaces and the grain boundaries. Moreover, the microstructure of the MLCC samples was evaluated by both electric property measurements and direct observation. From these results, we concluded that the grain boundaries controlled the leakage current as well as the lifetime.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd

    Analysis of Oxygen Vacancy Trapping at [001] Symmetric Tilt Grain Boundaries in Barium Titanate by Atomistic Simulations

    Takashi OyamaNobuyuki WadaHiroshi Takagi
    P.39-42页
    查看更多>>摘要：The role of grain boundaries (GBs) in the diffusion of oxygen vacancies (V_O~‥s) in barium titanate (BaTiO_3) and its mechanism were investigated using atomistic simulation techniques. It was found that GBs trapped V_O~‥s at specific sites in the course of the diffusion, and the excess energy reflecting structural distortion of the GB was closely related to the availability of the trapping. GBs therefore act as a resistance of the diffusion of V_O~‥s, suggesting that electrical degradation of multilayer ceramic capacitors (MLCCs), which is derived from vacancy diffusion, enables to be additionally improved by controlling GB structures in BaTiO_3-based dielectrics.
      原文链接:
    • NETL
    • NSTL
    • Trans Tech Publications Ltd