An ultrasonic shear wave attenuation study on Na+, K+, β″-alumina

An ultrasonic shear wave attenuation study has been carried out to investigate ionic motion in Na+- and K+-β″ -aluminas as a function of temperature. The attenuation peaks caused by sound absorption of hopping mobile ions are superimposed on background losses. The peaks indicate low activation energies (0.15−0.23 eV) for the ion-hopping process giving rise to GHz hopping rates at room temperature. The results suggest relaxation processes for the conducting ions in the β″-phase. In the case of mixed Na+/K+-β″ -alumina, the relaxation peak appears at a higher temperature than for the pure K+ sample, which suggests combined motion due to association of the two ions. This observation is discussed vis-á-vis the mixed alkali effect in Na-K-β″ -aluminas.