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

当Zn_2TiO_4中的Ti^<4+>离子部分被Ta^<5+>离子取代时，产生阳离子空位，并在高温下出现氧化离子传导。本文从结构分析和电化学测量两方面研究了缺陷的氧化离子传导机理，特别是缺陷结构与氧化离子传导的关系。在Zn_<2-x/2>Ti_<1-x>Ta_xO_4体系中，钽取代和阳离子空位的形成都发生在逆尖晶石型结构的四面体位置。基于脉冲中子衍射数据的Rietveld分析假设氧化物离子间隙非常小。由此推导出间隙扩散模型，即规则的氧化离子会向四面体上形成的阳离子空位移动，形成氧化离子空位，氧化离子通过该空位迁移。制备了Zn_2Ti_<1-2x>Ta_xAl_xO_4体系，该体系没有明显的阳离子空位。由于Ta^<5+>和Al^<3+>^-双取代并未出现氧化物离子的传导增强，证实了阳离子空位严格控制氧化物离子的传导。虽然阳离子空位浓度对氧化离子电导率的依赖性较弱，但没有检测到明显的阈值，说明氧化离子迁移的第一步必须有阳离子空位，然后利用新产生的氧化离子空位在之前置换的氧化离子所在的位置进行氧化离子扩散。本研究揭示了阳离子缺乏型Zn_2TiO_4基氧化物离子导体的氧化离子扩散机理。

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.