Anomalous conductivity effects in (Na,K) mixed crystals of the β-Al2O3 type

Anomalous behavior has been observed in the ionic conductivity of (Na,K) mixed crystals of the alkali gallates and aluminate of the β-Al₂O₃ type fast ion conductors. The conductivity goes through a minimum at some intermediate composition as a consequence of a maximum in the activation energy, and is most pronounced in the (Na,K)-β-gallate, followed by (Na,K)-β-Al₂O₃ and (Na,K)-β“-gallate. The effect is similar to the well-known “mixed alkali effect” in glasses. A second anomaly consisting of a pronounced increase in conductivity over about a 70° temperature range, without any permanent change in activation energy, was observed for some compositions of (Na,K)-β“-gallate.