1. V. A. Bokov and I. E. Mylnikova, Fiz. Tverd. Tela. 3 (1961) 871, in Russian. For translation see Soviet Physics Solid State 3 (1961) 613.
2. Jum Kuwata, K. Uchino and S. Nomura, Ferroelectrics 22 (1979) 863.
3. A. M. Glass, J. Appl. Phys. 40 (1969) 4699.
4. G. A. Smolenski, Proceedings of the 2nd International Meeting on Ferroelectricity, Kyoto (1969) (Phys. Soc. Japan, Tokyo, 1970) p. 26.
5. B. N. Rolov, Fizika Tverd. Tela 6 (1964) 2128, in Russian. For translation see Sovient Physics Solid State 6 (1976) 1676.