1. J. M. Binsma, L. J. Giling, and J. Bloem, J. Gyst. Growth,50, 429–436 (1980).
2. V. M. Burlakov, D. F. Rzaev, and V. N. Pyrkov, “Procedure for calculating optical characteristics from IR reflection spectra of single crystals” Troitsk (1984) (Preprint, Inst. Spektrosk. Akad. Nauk SSSR [in Russian].
3. I. V. Bodnar', A. G. Karoza, and G. F. Smirnova, Izv. Akad. Nauk SSSR, Neorg. Mater.,17, 224–227 (1981).
4. H. Neumann, Helvetica Physica Acta,58, 337–346 (1985).
5. N. M. Gasanly, A. Z. Magomedov, N. N. Melnik, and B. G. Salamov, Phys. Stat. Sol. (b),177, K31-K35 (1993).