1. S. Z. Shmurak and F. D. Senchukov, Fiz. Tverd. Tela (Leningrad) 15(10), 2976 (1973) [Sov. Phys. Solid State 15, 1985 (1973)].
2. A. I. Gubanov, Fiz. Tverd. Tela (Leningrad) 21(3), 730 (1979) [Sov. Phys. Solid State 21, 428 (1979)].
3. M. I. Molotskii, Kinet. Katal. 22(5), 1153 (1981).
4. A. A. Kusov, M. I. Klinger, and V. A. Zakrevskii, Fiz. Tverd. Tela (Leningrad) 31(7), 67 (1989) [Sov. Phys. Solid State 31, 1136 (1989)].
5. S. Z. Shmurak, Fiz. Tverd. Tela (St. Petersburg) 41(12), 2139 (1999) [Phys. Solid State 41, 1963 (1999)].