The effect of radiation upon the conductivity of crystals of the pure material was studied. The samples were irradiated with 60Co γ-rays, using a dose rate of 0.2Mrad/h at room temperature. It was found that, at temperatures greater than 90C, the product of conductivity and temperature was smaller for irradiated samples than for non-irradiated samples. The maximum deviation occurred between 140 and 160C. Here, the conductivity of a sample which had been irradiated to 1Mrad was about 10 times less than that of a non-irradiated sample. The thermal recovery of radiation-induced effects occurred at about 350C in less-irradiated samples whereas, in more heavily-irradiated samples, recovery occurred at about 560C. A systematic study was made of the variation in slope of the conductivity versus temperature plots, in region-III, as a function of the annealing temperature. In this region, the predominant process was the formation of divalent impurity cation-vacancy dipoles, and the slope of the plot here represented the cation migration energy; plus half of the dipole energy. The values which were found for the activation energy ranged from 0.92 to 1.32eV, when the annealing temperature was increased from 30 to 560C. When the annealing temperature was greater than 560C, the activation energy remained unchanged.

D.F.Mariani, J.Vignolo: Journal of Materials Science Letters, 1987, 6[9], 993-5