1. B. Chabot and E. Parthe, Acta Crystallogr. Sect. B 34, 645 (1978).
2. V. S. Kun, A. A. Boguslavskii, A. B. Kun, R. Sh. Lotfullin, V. B. Lazarev, and E. Yu. Peresh, in Proceedings of the Seventh Conference on Crystal Growth [in Russian], Vol. 3, Moscow (1988).
3. S. V. Melnikova, L. A. Shabanova, A. I. Zaitsev, S. A. Parshikov, O. A. Ageev, and K. S. Aleksandrov, Ferroelectrics 20, 163 (1996).
4. I. P. Aleksandrova, A. F. Bovina, O. A. Ageev, M. A. Popov, and A. A. Sukhovsky, J. Phys. Condens. Matter (in press).
5. T. A. Aslanyan and A. P. Levanyuk, Pis’ma Zh. Éksp. Teor. Fiz. 28, 76 (1978) (1978) [JETP Lett. 28, 70 (1978)].