1. For a review of A-15 compounds sec; D. Dew-Hughes, Cryogenics, 435, August, 1975.
2. J. K. Hulm and R. D. Blaugher, A.I.P. Conf. Proc. No. 4, 1, ed. D. H. Douglass, 1972.
3. M. C. Krupka, A. L. Giorgi, N. H. Krikorian, and E. G. Szklarz, J. Less-Common Metals 19, 113 (1969).
4. B.T. Matthias, Progress in Low Temperature Physics, Vol. II, p. 138, ed. C. J. Gorter, North-Holland Printing Co., 1957.
5. A.L. Giorgi, E.G. Szklarz and M.C. Krupka, A.I.P. Conf. Proc. No. 4, 147, ed. D. H. Douglass. 1972.