1. Ferroelectric Laboratory, Institute of Natural Sciences, Ural Federal University, 51 Lenin Ave., Ekaterinburg 620000, Russia
2. General Physics Institute of the Russian Academy of Sciences, 38 Vavilov Str., Moscow 119991, Russia
3. Institute of Materials Science, University of Silesia, 4 Uniwersytecka Str., Katowice PL-40-007, Poland