1. A. Giachello and P. Popper, Ceram. Int. 5 (1979) 110.
2. J. A. Mangels and G. J. Tennenhouse, Amer. Ceram. Soc. Bull. 59 (1980) 1216.
3. Idem, ibid. 60 (1981) 1306.
4. I. Colquhoun, D. P. Thompson, W. I. Wilson, P. Grieveson and K. H. Jack, Proc. Brit. Ceram. Soc. 22 (1973) 181.
5. S. Wild, P. Grievson, K. H. Jack and M. J. Latimer, ?Special Ceramics?, Vol. 5, edited by P. Popper (BCRA, Stoke-on-Trent, 1972) pp. 377?84.