1. M. A. Subramanian, G. Aravamudan, and G. V. Subba Rao,Progress in Solid State Chemistry (in press).
2. G. V. Bazuev, O. V. Markerova, V. Z. Oboldin, and G. P. Shevikin,Sov. Phys. Solid State 19 (11), 1913 (1977).
3. T. Shin-ike, G. Adachi, and J. Shiokawa,Mater. Res. Bull. 12, 1149 (1977).
4. J. E. Greedan,Mater. Res. Bull. 14, 13 (1979).
5. P. H. Hubert,Bull. Soc. Chem. France 1974, 2385.