1. A. G. Maklachkov and E. G. Ippolitov, Izv. AN SSSR. Neorg. Mater. 6, 1713 (1970).
2. P. Gredin, A. de Kozak, M. Quarton, et al., Z. Anorg. Allg. Chem. 619, 1088 (1993).
3. P. P. Fedorov, M. A. Sattarova, F. M. Spiridonov, and B. P. Sobolev, Zh. Neorg. Khim. 32, 163 (1987).
4. P. P. Fedorov, T. Trnovcova, V. A. Meleshina, et al., Neorg. Mater. 30, 406 (1994).
5. N. I. Sorokin, P. P. Fedorov, and B. P. Sobolev, Proceedings of the 10 Symposium on the Inorganic Chemistry of Fluorides, Moscow,
1998, p. 153.