1. N. F. Mott:Adv. Phys.,13, 325 (1964).
2. M. Born andK. Huang:Dynamical Theory of Crystal Lattices (Oxford, 1954).
3. J. de Launay:Solid State Physics, edited byF. Seitz andD. Turnbull, Vol.2 (New York, N. Y., 1956), p. 219;S. K. Joshi andA. K. Rajagopal:Solid State Physics, edited byF. Seitz, D. Turnbull andH. Ehrenreich, Vol.22 (New York, N. Y., 1968), p. 159.
4. K. Krebs:Phys. Rev.,138, A 143 (1965).
5. L. Chéveau:Phys. Rev.,169, A 96 (1968).