A NEW METHOD OF THE STOICHIOMETRY INCREASE OF THE LITHIUM NIOBATE NONLINEAR-OPTICAL CRYSTAL

Experimental and theoretical data on the influence of В2О3 flux on the crystal-melt system, the structural features, and the optical properties of a crystal of lithium niobate are summarized. The Gibbs energies of the borate impurities formation (Al4B2O9, CaB2O4, CaB4O7, Ca2B2O5, Ca3B2O6, PbB2O4) in a congruent composition charge of lithium niobate are calculated. It was found that the element boron, as an active complexing agent, in the composition of the В2О3 flux aligns the distribution coefficients of lithium (KLi) and niobium (KNb). Also, the element boron is able to prevent the transition of trace amounts of impurity metals into the structure of a lithium niobate crystal. Boron increases the ordering of structural units of the cation sublattice and distorts the anionic framework of the crystal. This is due to the fact that boron is embedded in the tetrahedral voids faces of the crystal structure in trace amounts (4∙10-4 mol.%). This leads to changes in bond lengths O-O of the oxygen octahedra O6, thereby changing polarizability oxygen-octahedral cluster NbO6, determining nonlinear optical and ferroelectric properties of the crystal.