Physicochemical and Optical Characteristics of LiNbO3 Single-Crystals Doped with Boron

Abstract

The chemical interaction in the Li₂CO₃–Nb₂O₅ and Li₂O–B₂O₃–Nb₂O₅ systems and crystallization features of LiNbO₃ crystals from the melts containing boron impurity are considered. Raman spectra of LiNbO₃:B crystals grown from a congruent melt containing ~0.55–1.24 mol % of B₂O₃ are studied. There are noticeable changes in the entire Raman spectrum upon doping with boron, which indicates a change in alternation of the main cations and vacancies along the polar axis of the LiNbO₃:B crystal and “perturbation” of oxygen octahedra. Moreover, expansion of oxygen octahedra is anisotropic with an increase in boron concentration in the melt. Boron, hardly entering the structure of the lithium niobate crystal, significantly changes the structure of the melt and thus has a significant effect on structure and physical characteristics of the LiNbO₃:B crystals. The results obtained for the LiNbO₃:B crystals are compared with those obtained for nominally pure stoichiometric (LiNbO_3stoich) and congruent (LiNbO_3cong) lithium niobate crystals.