1. S. V. Kun, E. Yu. Peresh, V. B. Lazarev, A. V. Orinchai, and M. I. Gorvat, Izv. Akad. Nauk SSSR, Neorg. Mater. 24, 1899 (1988); S. V. Kun, E. Yu. Peresh, V. B. Lazarev, and A. V. Kun, ibid. 27, 611 (1991); S. V. Kun, V. B. Lazarev, E. Yu. Peresh, A. V. Kun, and Yu. V. Voroshilov, ibid. 29, 410 (1993).
2. R. Jakubas, Z. Czapla, Z. Galewski, L. Sobczyk, O. J. Zogal, and T. Lis, Phys. Status Solidi A 93, 449 (1986).
3. A. Miniewicz, R. Jakubas, C. Ecolivet, and A. Girard, J. Raman Spectrosc. 25, 371 (1994).
4. R. Jakubas, U. Krzewska, G. Bator, and L. Sobczyk, Ferroelectrics 77, 129 (1988).
5. M. Maćkowiak, N. Weiden, and A. Weiss, Phys. Status Solidi A 119, 77 (1990).