1. V. I. Alshits, E. V. Darinskaya, T. M. Perekalina, and A. A. Urusovskaya, Fiz. Tverd. Tela 29, 467 (1987) [Sov. Phys. Solid State 29, 265 (1987)].
2. V. I. Alshits, E. V. Darinskaya, M. V. Koldaeva, and E. A. Petrzhik, Kristallografiya 48, 826 (2003) [Crystallogr. Rep. 48, 768 (2003)].
3. A. A. Urusovskaya, V. I. Alshits, A. E. Smirnov, and N. N. Bekkauer, Kristallografiya 48, 855 (2003) [Crystallogr. Rep. 48, 796 (2003)].
4. Yu. I. Golovin, Fiz. Tverd. Tela 46, 769 (2004) [Phys. Solid State 46, 789 (2004)].
5. R. B. Morgunov, Usp. Fiz. Nauk 174, 131 (2004) [Phys. Usp. 47, 125 (2004)].