The electrical and thermal properties of single crystals were studied over a wide temperature range. It was found that a phase transformation at 483K was associated with an anomaly in the conductivity of crystals which were oriented along the b-axis. A transition to a high-temperature fast ionic phase was observed at about 588K in crystals which were oriented along [101] or [10¯1] directions. The highest conductivity was observed for measurements made perpendicular to the b-axis.

A.K.Ivanov-Schitz, J.Schoonman: Solid State Ionics, 1996, 91[1-2], 93-9