1. S. E. RASMUSSEN and R. G. HAZELL,Acta Chem. Scand. Ser. A. 32 (1978) 785.
2. L. R. TESTARDI, in ?Physical Acoustics? Vol. 10 (Academic Press, New York and London, 1973).
3. M. WEGER and I. B. GOLDBERG, in ?Solid State Physics?, Vol. 28 (Academic Press, New York and London, 1973).
4. G. SREERAMACHANDRA MURTHY, K. SATYANARAYANA MURTHY and S. E. RASMUSSEN, unpublished work (1981).
5. K. V. KRISHNA RAO, S. V. NAGENDER NAIDU and K. SATANARAYANA MURTHY,J. Phys. Chem. Sol. 29 (1968) 245.