Measurements were made of the ionic conductivity, at temperatures of between 300 and 675C, of pure single crystals. The conductivity parameters were determined in the high-temperature region from a least-squares straight-line Arrhenius plot. The results could be described by:

σT (SK/cm) = 2.91 x 109 exp[-2.017(eV)/kT]

H.L.Downing, R.J.Friauf: Physical Review B, 1975, 12[12], 5981-9