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2. Yu. S. Kuz’minov, Electrooptical and Nonlinear Optical Lithium Niobate Crystal (Nauka, Moscow, 1987) [in Russian].
3. T. Volk and M. Wohlecke, Lithium Niobate. Defects, Photorefraction and Ferroelectric Switching (Springer, Berlin, 2008).
4. M. N. Palatnikov and N. V. Sidorov, in Oxide Electronics and Functional Properties of Transition Metal Oxides (Nova Sience, USA, 2014), Chap. 2, p. 31.
5. N. V. Sidorov, T. R. Volk, B. N. Mavrin, and V. T. Kalinnikov, Lithium Niobate. Defects, Photorefraction, Vibrational Spectrum, Polaritons (Nauka, Moscow, 2003) [in Russian].