Structure, electrical properties, and conduction mechanism of new germanate mixed Zn-doped In2Ge2O7 conductors

Mixed electronic and oxide ionic conduction was introduced in InGe2O7 containing isolated Ge2O7 units through the substitution of Zn2+ for In3+. The solid solution limit of Zn doping in In2−xZnxGe2O7−0.5x is 0–0.2, as confirmed by Rietveld refinements and systematic experiments. The bulk conductivities of the obtained In1−xZnxGe2O7−0.5x (x = 0.2) can reach 1.62 × 10−2 S cm−1 at 1000 °C with oxygen transport number of ∼20%. Moreover, variable temperature XRD patterns of In1−xZnxGe2O7−0.5x (x = 0.2) show the superior phase stability in the temperature region of 25–1000 °C with potential applications in electrode materials for SOFCs. Oxide ion conduction is ascribed to the preferred oxygen vacancies of the O1 site introduced by the substitution of Zn2+ for In3+, and the BVEL calculations indicate that the migration of oxygen vacancies is achieved by oxygen exchange between adjacent Ge2O7 units and exhibits two-dimensional anisotropic transport in monoclinic In2Ge2O7.