1. S. FAUCHY and J. GUIGONIS,L'Indus. C�ram. 641 (1971) 493.
2. T. KANEKO and H. YAMAMOTO, Proceedings of the 10th International Congress on Glass, Kyoto (1974) pp. 8?79.
3. S. URNES,J. Amer. Ceram. Soc. 56 (1973) 514.
4. G. H. CHARTIER, P. JAUSSAUD, A. D. de OLIVEIRA and O. PARRIAUX,Electron. Lett. 14 (1978) 132.
5. H. G�TZ, G. HELLAND and H. A. SCHAEFFER,Glasstechn. Ber. 52 (1979) 99.