Study in Conduction Mechanism of the Cation Deficient-type Oxide Ion Conductors

当Ti2TiO4中的Ti^&lt；4&gt；离子被Ta^&lt；5&gt；离子部分取代时，在高温下产生阳离子空位，并出现氧化物离子导电现象。本文通过结构分析和电化学测试，研究了氧化物离子的导电机理，特别是缺陷结构与氧化物离子导电的关系。在锌钛尖晶石型结构的四面体位置，Ta_xO_4体系中，Ta_xO_4和Ta_xO_4体系中，Ta_xO_4Rietveld分析是基于脉冲中子衍射数据进行的，假设氧离子间隙的数量很少。由此推导出间隙扩散模型，即规则的氧离子向四面体位置上的阳离子空位移动，形成氧离子空位，氧离子通过该空位迁移。并制备了无明显阳离子空位的体系。由于Ta^&lt；5&gt；和Al^&lt；3&gt；^-双取代没有引起氧离子电导增强，证实了阳离子空位严格控制着氧离子电导。虽然阳离子空位浓度对氧化物离子电导率的依赖关系表现出较低的功率，但没有检测到任何明显的阈值，这表明阳离子空位是氧化物离子迁移的第一步，然后利用取代的氧化物离子先前所在的新生成的氧化物离子空位进行氧化物离子的扩散。本研究揭示了阳离子缺陷型锌钛酸基氧化物离子导体的氧化物离子扩散机理。

When Ti^<4+> ions in Zn_2TiO_4 were partly substituted by Ta^<5+> ions, cation vacancies were created and oxide ion conduction appears at elevated temperatures. In the present study, oxide ion conduction mechanism, especially on the relationship between the defect structure and oxide ion conduction, were investigated in terms of the structure analyses and electrochemical measurements.In Zn_<2-x/2>Ti_<1-x>Ta_xO_4 system, both tantalum substitution and cation vacancy formation occur at tetrahedral site of the inverse spinel-type structure. Rietveld analyses based on the pulsed neutron diffraction data were carried out assuming very small mount of oxide ion interstitials. As the result, interstitialcy diffusion model were deduced, i.e., the regular oxide ion would shift toward the cation vacancy crated at the tetrahedral site, forming the oxide ion vacancy via which the oxide ion migrate.Zn_2Ti_<1-2x>Ta_xAl_xO_4 system, which possesses no significant cation vacancy, was also prepared. Since the oxide ion conduction enhancement does not appear by means of Ta^<5+> and Al^<3+>^-dual substitution, it was confirmed that the cation vacancy strictly govern the oxide ion conduction. Although cation vacancy concentration dependence of the oxide ion conductivity showed the power low, any obvious threshold was not detected, indicating that the cation vacancy is necessarily for the first step of the oxide ion migration and then oxide ion diffusion is carried out by using the newly created oxide ion vacancy where the displaced oxide ion previously located.The present study revealed the oxide ion diffusion mechanism of the cation-deficient-type Zn_2TiO_4 based oxide ion conductors.