1. S. WILLIAMS, PhD thesis, Cambridge University (1983).
2. T. H. MAO, P. W. R. BEAUMONT and W. C. NIXON,J. Mater. Sci. Lett. 2 (1983) 613.
3. D. G. GILBERT, P. W. R. BEAUMONT and W. C. NIXON, in ?Proceedings of ICM4?, Stockholm, August 1983, edited by J. Carlsson and N. G. Ohlson (Pergamon, 1983) p. 705.
4. S. L. OGIN, private communication.
5. M. L. C. JONES, PhD thesis, University of Liver-pool (1981).