Abstract
A‐C and d‐c conductivities of monocrystals of the gallium analogs of β‐ and β''‐alumina were measured over the temperature range from room temperature to 350°C, using both reversible and ion‐blocking electrodes. Conductivities of the gallates are substantially higher than those of the corresponding aluminates, and Na‐β''‐gallate has the highest conductivity [≃ 1 (Ω‐cm)−1 at 300°C] that has been reported for any alkali ion conductor. The transport number for electrons in the gallates is less than 10−6 at 300°C.