1. E. V. Zharikov, Yu. S. Kuz’minov, V. V. Osiko, and T. M. Sarzhevskaya, Growth of Crystals, vol. 12 [in Russian], Izd. EGU, Erevan (1977), p. 219. [English translation: Consultants Bureau, New York (198), p. 225].
2. A. Lidiard, Ionic Conduction in Crystals [Russian translation], IL, Moscow (1962).
3. W. A. Bonner, J. R. Carruthers, and H. M. O’Bryan Jr., Mat. Res. Bull., 5: 243 (1970).
4. S. Singh, D. A. Draegert, and J. E. Geusic, Phys. Rev. B, 2: 2709 (1970).
5. S. Singh, H. J. Levinstein, and L. G. Van Uitert, Appl. Phys. Lett., 16: 176 (1970).