1. Lubezky, I., and Tannhauser, D. S., J. Crystal Growth, 17, 162 (1972).
2. Spear, W. E., and Tannhauser, D. S., Phys. Rev., B7, 831 (1973).
3. Bosnian, A. J., and van Daal, H. J., Adv. Phys., 19, 1 (1970).
4. van Daal, H. J., Proceedings of the Second International Conference on Low Mobility Materials, Taylor and Francis, Eilat (1971), p. 17.
5. Spear, W. E., J. Non-Cryst. Solids, 1, 197 (1969).