1. V. I. Al’shits, E. V. Darinskaya, T. M. Perekalina, and A. A. Urusovskaya, Fiz. Tverd. Tela (Leningrad) 29, 467 1987) [Sov. Phys. Solid State 29, 265 (1987)].
2. V. I. Al’shits, E. V. Darinskaya, I. V. Gektina, and F. F. Lavrent’ev, Kristallografiya 35, 1014 1990) [Sov. Phys. Crystallogr. 35, 597 1990)].
3. V. I. Al’shits, E. V. Darinskaya, and E. A. Petrzhik, Fiz. Tverd. Tela (Leningrad) 34, 155 1992) [Sov. Phys. Solid State 34, 81 (1992)].
4. V. I. Al’shits, E. V. Darinskaya, and E. A. Petrzhik, Fiz. Tverd. Tela (St. Petersburg) 35, 320 1993)[Sov. Phys. Solid State 35, 162 1993)].
5. V. I. Al’shits, R. Voska, E. V. Darinskaya, and E. A. Petrzhik, Fiz. Tverd. Tela (St. Petersburg) 35, 70 (1993) [Sov. Phys. Solid State 35, 37 (1993)].