1. I. Schoonman, G. A. Kocteweg, and R. W. Bonne, Solid State Commun. 16(1), 9 (1975).
2. I. H. Beaumont, A. I. Bourdillon, and I. Bordas, J. Phys. C.: Solid State Phys. 10(5), 767 (1977).
3. I. V. Murin and O. V. Glumov, Fiz. Tverd. Tela (Leningrad) 23(2), 624 (1981).
4. I. V. Murin, O. V. Glumov, and S. V. Chernov, Abstracts of Papers, VII All-Union Symposium on Chemistry of Inorganic Fluorides (Moscow, 1984), p. 233.
5. B. A. Kulikov and N. V. Sabo, Zh. Fiz. Khim. 50(5), 1185 (1976).