1. L. Wei, D. Guiqing, H. Qingzhen, Z. An, and L. J. Kni, J. Phys. D 23, 1073 (1990).
2. I. N. Ogorodnikov, A. Yu. Kuznetsov, A. V. Kruzhalov, and V. A. Maslov, Rad. Meas. 24, 423 (1995).
3. V. Yu. Yakovlev, Fiz. Tverd. Tela (Leningrad) 26, 3334 (1984) [Sov. Phys. Solid State 26, 2003 (1984)].
4. V. A. Maslov, L. A. Olkhovskaya, V. V. Osiko, and E. A. Shcherbakov, Abstracts of the 10th International Conference Crystal Growth, San Diego (1992), p. 11.
5. I. N. Ogorodnikov, V. Yu. Ivanov, A. Yu. Kuznetsov, A. V. Kruzhalov, and V. A. Maslov, Pisma Zh. Tekh. Fiz. 19(11), 1 (1993) [Tech. Phys. Lett. 19, 669 (1993)].