3 Nafziger, R. H., High Temp. Sci., 7 (1975) , 179．
[4]
4 Levin, E. M.; Robbins, C. R.; McMurdie, H. F., Phase Diagrams for Ceramists, Second Edition, 1969, p. 209, 210, 113; Phase Diagrams for Ceramists, 1969 Supplement, p. 36, 85．
[5]
5 Johnson, R. E.; Muan, A.; J. Am. Ceram. Soc., 48 (1965) , 359．
[6]
6 Stephenson, I. M.; White, J., Trans. Br. Ceram. Soc., 66 (1967) , 443．
