The mixed alkali conductivity anomaly in as-growm K-β-gallate with substituted sodium

K-β-gallate is a potassium/gallium isomorph of the two-dimensional fast ion conductor, β-alumina. The composition, K2O·8.10Ga2O3, requires 36% excess K over that of the stoichiometric compound. The charge on this excess is compensated by interstitial oxygens in the conduction plane. The crystal exhibits a strong "mixed alkali effect" when part of the K is replaced by Na. At {reversed tilde equals}20 atom per cent Na, the conductivity at room temperature goes through a minimum about 3- 1 2 orders of magnitude lower than that expected from extrapolation between the conductivities of the single alkali end member crystals. An explanation of the effect based on site preference by the two alkali ions is proposed. © 1981.