1. R. Swalin, ?Thermodynamics of Solids? (John Wiley & Sons Inc., New York, 1962).
2. G. G. Libowitz, J. Solid State Chem. 1 (1969) 50.
3. E. F. Gurnee, J. Chem. Educ. 46 (1969) 80.
4. W. Ruppel, A. Rose, and H. J. Gerritsen, Helv. Phys. Acta, 30 (1957) 238; see also, A. Rose, ?Concepts in Photoconductivity and Allied Problems? (Interscience, New York, 1963) final chapter.
5. A. K. Vijh, J. Phys. Chem. Solids 29 (1968) 2233; idem, J. Electrochem. Soc. 116 (1969) 353.