1. Taras Shevchenko National University of Kyiv, 64 Volodymyrs'ka Str., 01601 Kyiv, Ukraine
2. Institute for Single Crystals NAS of Ukraine, Nauki Ave., Kharkiv 61001, Ukraine
3. National Pedagogical Dragomanov University, Pyrogova Str., 9, 01601 Kyiv, Ukraine