为了探索CaCu3Ti4O12(CCTO)高介电性的起因机制, 利用固相反应工艺制备了CCTO陶瓷样品, 对其电学性质进行了研究. 在40 Hz~100 MHz测量范围内, 其室温下的介电频谱在1 MHz附近呈现一个类Debye型弛豫, 而高温介电频谱分别在1 kHz以下和1 MHz附近呈现两个类Debye型弛豫. 抛除表面层的同一个样品分别溅射金电极和烧渗银电极后升温测量其介电频谱, 发现低频介电弛豫对电极的金属类型高度敏感, 而高频介电弛豫与电极的金属类型无关, 与材料微观结构存在着密切的关系. 因此推断: CCTO低频介电弛豫起源于样品与电极之间的耗尽层效应, 而高频介电弛豫起源于高阻态的晶界与半导化的晶粒形成内部阻挡层电容效应.
CaCu3Ti4O12 (CCTO) is one typical giant dielectric material with large ε' value in the order of 104, however, origin of giant dielectric permittivity in it is still controversial so far. In order to explore its possible origin, the dielectric properties and complex impedance of CCTO ceramics prepared via solid-state reaction method were investigated. Within the frequency range of 40 Hz-100 MHz, only one Debye-type relaxation around 1 MHz is observed at room temperature, while high-temperature dielectric dispersion shows two Debye-type relaxations below 1 kHz and around 1 MHz, respectively. The same sample surface-polished with Ag-paint electrodes and sputtered Au electrodes is measured at high temperature, respectively. It is revealed that the dielectric relaxation in the low frequency range changes significantly with the type of electrodes, while the dielectric relaxation in the high frequency range is independent of the type of electrodes, but exists closely relationship with the microstructure of samples. The two dielectric relaxations are thus suggested to originate from an electrode polarization effect and an internal barrier layer capacitance effect associated with insulating grain boundaries and semiconducting grains, respectively.
参考文献
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