1. A. B. Lidiard, Ionic Conductivity (Springer, Berlin, 1957; Inostrannaya Literatura, Moscow, 1962), in Handbuch der Physik, Ed. by S. Flugge, p. 246.
2. K. Aboagye and R. J. Friauf, Phys. Rev. B 11, 1654 (1975).
3. P. A. Varotsos and K. Alexopoulus, J. Phys. Chem. Solids 39, 759 (1978).
4. A. K. Ivanov-Schitz and I. V. Murin, Ionics of Solid State (S.-Peterb. Gos. Univ., St. Petersburg, 2001) [in Russian].
5. W. Hayes, Contemp. Phys. 27(6), 519 (1986).