1. Ashcroft N. W., N. D. Mermin, Solid State Physics, Holt, Rinhart and Winston, N. Y. 1976, p. 443.
2. Weiss R., Solid State Physics for Metallurgists, Pergamon Press, N. Y. 1963, p. 305.
3. Zener, C., Phys. Rev.71, 846 (1947).
4. Scott, J. F., Rev. Mod. Phys.10, 401 (1961).
5. Pytte, E., Phys. Rev.B4 1094 (1971).