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

Abstract

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 In_2−xZn_xGe₂O_7−0.5x is 0–0.2, as confirmed by Rietveld refinements and systematic experiments. The bulk conductivities of the obtained In_1−xZn_xGe₂O_7−0.5x (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 In_1−xZn_xGe₂O_7−0.5x (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.