1. B. E. Yoldas,J. Amer. Ceram. Soc. 59 (1980) 479.
2. D. W. Hoffman, R. Roy andS. Komarneni,ibid. 67 (1984) 468.
3. B. E. Yoldas,ibid. 65 (1982) 387.
4. K. Okada andN. Otsuka,ibid. 69 (1986) 652.
5. J. C. Pouxviel, J. P. Boilot, A. Dauger andL. Hubert, in ?Better Ceramics through Chemistry II?, MRS meeting Palo Alto, edited by C. J. Brinker, D. E. Clark and D. R. Ulrich, Vol. 73 (Material Research Society, Pittsburgh, 1986) p. 269.