Investigation of the structural perfection of lithium niobate and tantalate single crystals and ceramics of different composition and technologies on the first and second orders raman scattering spectra

The results of a study of the structural perfection of crystals and ceramics of lithium niobate and lithium tantalate of various compositions are presented. In solid solutions of the LiNbxTa1-xO3 family with 0.4 ≤ x ≤ 0.6, lines were found in the Raman spectra, both of the first (in the range of 150–900 cm–1) and of the second order, located in the range of 900–2000 cm–1. Second-order Raman lines in the range 900–2000 cm–1 were also recorded by us in single crystals of single-doped lithium niobate and lithium tantalate LiNbO3:Tb (2.24 wt. %), LiTaO3:Cr (0.005 wt. %), and double-doped lithium tantalate LiTaO3:Cr (0.2):Nd (0.45 wt. %). The observed lines in the range 900–2000 cm-1 are explained as a manifestation of overtone processes corresponding to biphonons.