Temperature dependence of refractive indices of LiNbO_3, LiTaO_3 and (Ba, Na)NbO_3 relative crystals: similarity and difference

摘要

Detailed refractive indices measurements of transparent LiNbO_3, LiTaO_3 and (Ba, Na)NbO_3 crystals in the temperature region 20-700 °C are reported. It is obtained that, besides the similarity in chemical compound and structure, optical properties of these crystals are different. The important common feature of lithium niobate and lithium tantalate crystal is dispersion of thermooptical coefficients. It is shown that phase transitions with different character take place at ～ 600° in all measured crystals. Phase transitions are accompanied such optical appearances as diffraction and coexistence of phases.