1. R. C. A. Miller, Phys. Rev. 134, A1313 (1964).
2. S. K. Esayan, V. V. Lemanov, and A. M. Arutunyan, Ferroelectr. Lett. 1, 13 (1983).
3. É. V. Bursian and V. V. Rychgorskii, Fiz. Tverd. Tela (St. Petersburg) 41, 1076 (1999) [Phys. Solid State 41, 980 (1999)].
4. V. G. Zalesskii, É V. Bursian, and V. V. Maslov, Izv. Akad. Nauk, Ser. Fiz. 60(10), 63 (1996).
5. É. V. Bursian, V. G. Zalesskii, A. A. Luzhkov, and V. V. Maslov, Pis’ma Zh. Éksp. Teor. Fiz. 64, 247 (1996) [JETP Lett. 64, 270 (1996)].