1. W. Klemm and H. Westlinning:Z. anorg. Chem., 1940, vol. 245, pp. 365–80.
2. B. C. Gerstein, P. L. Chung, and G. C. Danielson:J. Phys. Chem. Solids, 1966, vol. 27, pp. 1161–65.
3. P. Beardmore, B. W., Howlett, B. D. Lichter, and M. B. Bever:Trans. TMS-AIME, 1966, vol. 236, pp. 102–8.
4. V. N. Eremenko and G. M. Lukashenko:Izv. Akad. Nauk SSSR. Neorg. Mat., 1965, vol. 1, pp. 1296–97.
5. J. F. Smith: Iowa State University, Ames, Iowa. Quoted in Ref. 6.