1. Metals Handbook, 8th ed., American Society for Metals, Metals Park, OH, 1961, vol. 1, pp. 443-53.
2. Metals Handbook, 9th ed., American Society for Metals, Metals Park, OH, 1980, vol. 3, pp. 269-84.
3. J.P. Guha and D. Kolar:J. Less-Common Metals, 1972, vol. 29, pp. 33–40.
4. Metals Handbook, 8th ed., American Society for Metals, Metals Park, OH, 1961, vol. 8, p. 402.
5. G. V. Samsonov and I.M. Vinitskii:Handbook of Refractory Compounds, IFI/Plenum Data Co., New York, NY, 1980, p. 98.