1. V. A. Isupov, in Ferroelectric and Antiferroelectric Materials [in Russian], edited by G. A. Smolenskii, Nauka, Leningrad, 1971, Chap. 19.
2. V. A. Isupov, in Physics of Ferroelectric Phenomena [in Russian], edited by G. A. Smolenskii, Nauka, Leningrad, 1985, Chap. 15.
3. S. E. Cummins and L. E. Cross, Appl. Phys. Lett. 10, 14 (1967).
4. V. A. Isupov, Zh. Neorg. Khim. 39, 731 (1994).