An inverse spinel-type oxide solid solution was formed in samples which were based upon the above composition. Substituted systems of the form, Zn2-x/2Ti1-xTaxO4, exhibited fairly high oxide ion conductivities; which increased with increasing Ta content (and number of cation vacancies). A sample with x = 0.35 had an oxide ion conductivity of 0.002S/cm at 1000C. It was concluded that the addition of more than 70% of substituted Ta led to the appearance of a mixed phase and to a decrease in conductivity. The oxide ion conduction in these spinel-type phases was attributed to interstitialcy oxide ion diffusion via cation vacancies.

T.Esaka, T.Ikebe, M.Kamata: Solid State Ionics, 1995, 76[3-4], 237-42