1. Acoustic Crystals: A Handbook, Ed. by M. P. Shaskol’skaya (Nauka, Moscow, 1982) [in Russian].
2. F. Canal, M. Grimsditch, and M. Cardona, Solid State Commun. 29, 523 (1979).
3. B. G. Mytsyk, A. S. Andrushchak, N. M. Demyanyshyn, et al., Appl. Opt. 48, 1904 (2009).
4. Yu. I. Sirotin and M. P. Shaskol’skaya, Fundamentals of Crystal Physics (Nauka, Moscow, 1979) [in Russian].
5. B. G. Mytsyk, A. S. Andrushchak, and G. I. Gas’kevich, Ukr. Fiz. Zh. 52, 800 (2007).