1. Yu. S. Kuz’minov, Lithium Niobate and Lithium Tantalate: Materials for Nonlinear Optics (Nauka, Moscow, 1975) [in Russian].
2. 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].
3. T. R. Volk and N. M. Rubinina, Fiz. Tverd. Tela 33 (4), 1192 (1991).
4. U. Schlarb, M. Woehlecke, B. Gather, et al., Opt. Mater. 4, 791 (1995).
5. T. S. Chernaya, T. R. Volk, I. A. Verin, et al., Crystallogr. Rep. 53 (4), 573 (2008).