1. Report S M A-27, 1977; Int. Center for Diffraction. Data, Swarthmore, Penn., USA.
2. U.S. National Bureau of Standards Circulars (i) 539, Vol. I. 1953; (ii) 539, Vol. II, 1953; (iii) 539. Vol. III, 1954; (iv) 539, Vol. IV, 1955; (v) 539, Vol. VII, 1957; (vi) 25, Sec.8, 1970; (vii) 25, Sec.3, 1964; (viii) NBS result quoted by K.O. Mclean and C.S. Smith, J. Phys. Chem. Solids, 33, 279, 1972.
3. Landolt-Bornstein, Numerical data and Functional relationships in Sci. and Tech., New Series, Group Ill. Vol. 7, Part a, Ed. K.H. Hellwege and A.M. Hellwege, Springer Verlag, Heidelberg, 1973 and references therein.
4. K.K.Srivastava and H.D. Merchant. J. Phys. Chem. Solids, 34, 2069, 1973.
5. V.T. Deshpande and D.B. Sirdeshmukh, Acta Cryst., 14. 353, 1961.