1. H. A. Aulich, K. -H. Eisenrith, H. -P. Urbach andJ. G. Grabmaier, in Proceedings of the 3rd Symposium on Materials and New Processing Technologies for Photovoltaics, Vol. 82?8, Montreal, May 1982 (Electrochemistry Society, Pennington, USA) pp. 177?81.
2. D. Helmreich, E. Sirtl andJ. Dietl, ?Crystals, Growth, Properties, and Applications? (Springer-Verlag, Berlin, Heidelberg, New York, 1981) pp. 43?107.
3. H. P. Hood andM. E. Nordberg, U.S. Patent 2 221 709 (1940).
4. L. L. Hench,J. Non-Cryst. Solids 25 (1977) 343.
5. B. E. Ramachandran, B. C. Pai andN. Balasubramani,J. Amer. Ceram. Soc. 63 (1980) 1.