1. F. A. Kroger, The Chemistry of Imperfect Crystals. North Holland Publishing Company, Amsterdam. 1964.
2. S. Anderson, B. Collen, U. Kuylensierna, and M. Magneli, Acta Chem. Scand., 11 1641 (1957).
3. I. V. Vinokurov and V. A. loffe, Soc. Phys. Solid State, 11 207 (1969).
4. R. E. Carter and F. D. Richardson, J. Metals, 6 1244 (1954).
5. W. K. Chen and R. A. Jackson, J. Phys. Chem. Solids, 30 1309 (1969).