1. E. A. Kuz'min, V. V. Ilyukhin andN. V. Belov, Soviet Phys., Dokl., 12 (1967) 293. (Translation of Dokl. Akad. Nauk SSSR, 173 (1967) 1078).
2. J. K. Brandon andI. D. Brown, Can. J. Chem., 46 (1967) 933.
3. G. Brunton, Mater. Res. Bull., 8 (1973) 271.
4. Yu. I. Vesnin andL. A. Khripin, Russ. J. Inorg. Chem., 11 (1966) 1188. (Translation of Zh. Neorgan. Khim., 11 (1966) 2216.
5. U. Klement andG. M. Schwab, Z. Krist., 114 (1960) 170.