1. Popov, S.N.; Krainik, N.N.; Myl'Nikova, I.E.: Izv. Akad. Nauk SSSR Ser. Fiz. 33(2), 271–273 (1969)
2. Popov, S.N.: Phys. Solid State 41(7), 1175–1181 (1999)
3. Ignatov, B.G.; Aleksandrov, A.L.; Ekimovskikh, I.A.; Semin, G.K.: Zavod. Lab. 40(4), 403–404 (1974)
4. Belyaev, L.M.; Lyakhovitskaya, V.A.; Bryukhova, E.V.; Babushkina, T.A.; Zhukov, A.P.; Naumov, A.S.; Tambovtsev, D.A.; Semin, G.K.: Repts. of the All-Union Conf. on Ferroelectricity (Rega) 36 (1968)