The alternating-current conductivity was measured as a function of pressures of up to 1.8GPa, at temperatures ranging from 300 to 1100K. The data revealed a decrease in conductivity with pressure, and a sharp jump at the orthorhombic/hexagonal phase transition. The activation energy for ionic conduction in the hexagonal phase was effectively independent of pressures of up to about 1GPa, where there was a sharp drop. The activation volume was strongly temperature-dependent for both the orthorhombic and hexagonal phases.

E.A.Secco, R.A.Secco: Solid State Ionics, 1996, 86-88[1], 147-54