1. C.M. Wolfe and K.H. Nichols, Appl. Phys. Lett., Vol.31, 356 (1977).
2. Final Scientific Report No. 59356-6, Washington Uni- versity, St. Louis, Mo. (1979).
3. L.A. Girifalco, Atomic Migration in Crystals, Blais- dell Publishing Company, 1964.
4. R.C. Miller and F.M. Smits, Phys. Rev., Vol. 107, 65 (1957).
5. F.A. Kröger, The Chemistry of Imperfect Crystals, 2nd ed., Vol. 1, North-Holland, Amsterdam, 1973.