Photorefraction Resistance of Na₂O-Doped Lithium Niobate Single Crystals

Na₂O-doped (up to 3mol% Na in the melt) LiNbO₃ crystals have been grown by the Czochraski method. The experimental results show that Na₂O dopants can increase the ability of LiNbO₃ to resist light-induced optical damage, but the photorefraction of LiNbO₃ : Na(3 mol%) is larger than that of LiNbO₃ : Na (1 mol%) and the absorption edge of the former crystal has a longer wavelength compared with that of the latter. These two abnormal phenomena were interpreted as that some ilmenite structure (NaNbO₃) regions are formed in doped LiNbO₃ crystals with the increasing dopant concentration of Na₂O.