| Budget Amount *help |
¥1,800,000 (Direct Cost: ¥1,800,000)
Fiscal Year 2006: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2005: ¥1,300,000 (Direct Cost: ¥1,300,000)
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| Research Abstract |
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.
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