1. A. A. VAIPOLIN, N. A. GORYUNOVA, E. O. OSMANOV and J. V. RUD,Dokl. Akad. Nauk SSSR 160 (1965) 633.
2. N. A. GORNUYOVA, B. V. BARANOV, V. S. GRIGORYEVA, L. V. KRADINOVA, V. A. MAKSIMOVA and V. D. PROCHUKHAN,Izv. Akad. Nauk SSSR Neorgan. Mater. 4 (1968) 1060.
3. A. P. BHATTACHERJEE, MS thesis, University of Illinois, Urbana/Champaign (1981).
4. S. A. BORSCHEVSKII, N. A. GORYUNOVA, F. P. KESAMANLY and D. N. NASLEDOV,Phys. Status Solidi 21 (1967) 9.
5. A. ABRAHAM, V. VORLICEK and M. ZAVETIVA,Czech. J. Phys. B18 (1968) 958.