1. F. Seitz, The Modern Theory of Solids, MeGraw Hill Book Co, Inc., New York, 1940, Pages 65–72.
2. N.F. Mott and R.W. Gurney, The Electronic Processes in ionic crystals, Oxford University Press, Oxford, 1946.
3. A.B. Lidiard, Handbuch der Physik, Springer-Verlag., Gottingen, 1957, Pages 250–255.
4. O. Stasiw, Electron and Ion Processes in Crystals, Springerverlog., Berlin, 1959.
5. A.F. Ioffe, Physics of Semi-conductors, Infosearch Ltd., London, 1960, Pages 2–5.