1. R. F. Davis andJ. A. Pask, in ?High Temperature Oxides?, Part IV, edited by A. M. Alper (Academic Press, New York, 1971) p. 37.
2. W. D. Kingery, H. K. Bowen andD. R. Uhlman, in ?Introduction to Ceramics? (Wiley, New York, 1975) p. 583.
3. P. A. Lessing, R. S. Gordon andK. S. Mazdiyasni,J. Amer. Ceram. Soc. 58 (1975) 149.
4. R. Roy,ibid. 39 (1956) 145.
5. J. D. Crofts andW. W. Marshall,Trans. Brit. Ceram. Soc. 66 (1967) 121.