1. N. F. Mott and R. W. Gurney, Electronic Processes in Ionic Crystals, 2nd edn., Dover (1948).
2. V. G. Gorshkov, A. S. Epifanov, A. A. Manenkov, et al., Tr. Inst. Obshch. Fiz. Akad. Nauk SSSR,4, 99 (1986).
3. D. I. Vaisburd, G. A. Mesyats, V. A. Naminov, et al., Dokl. Akad. Nauk SSSR,265, No. 5, 1113 (1982).
4. W. L. Emkey and W. J. Van Sciver, Phys. Rev. B,5, No. 2, 610 (1972).
5. G. Kötitz, H. Mothes, G. Fersh, et al., Phys. Status Solidi,31, No. 2, 371 (1975).