1. A. V. Golubkov, E. V. Goncharova, V. P. Zhuze, G. M. Loginov, V. M. Sergeeva, and I. A. Smirnov, Physical Properties of Rare Earth Chalcogenides (Nauka, Leningrad, 1973) [in Russian].
2. V. V. Kaminskii, Tech. Phys. Lett. 39, 673 (2013).
3. T. Schleid and F. Lissner, J. Less-Common. Met. 175, 309 (1991).
4. D. O. Neill, R. M. Bowman, and J. M. Gregg, Appl. Phys. Lett. 77, 1520 (2000)
5. Impedance Spectrography Theory, Experiment, and Applications, Ed. E. Barsoukov and J. R. Macdolald (Wiley, New Jersey, 2005).