The ionic and superionic conductivities of single crystals were measured as a function of frequency at various temperatures. The temperatures ranged from 400 to 1010C, and the frequencies ranged from 10Hz to 10MHz. At all temperatures, the apparent conductivity of the sample depended upon the crystal thickness and the frequency. An analysis was performed using complex impedance diagrams, and it was concluded that the actual conductivity was frequency-independent within this temperature range. The intrinsic enthalpy was deduced to be 2.04eV, the formation enthalpy of the anti-Frenkel defect was 2.0eV, and the enthalpy of defect migration was equal to 1.04eV.

G.A.Evangelakis, D.Miliotis: Physical Review B, 1987, 36[9], 4958-61