Structural features and optical properties of nominally pure LiNbO$_{3}$ crystals grown from a charge containing B$_{2}$O$_{3}$

It is shown that application of B$_{2}$O$_{3}$ as a flux allows one to obtain nominally pure composition-homogeneous LiNbO$_{3}$ crystals characterized by high, close-to-stoichiometry ordering of structural units of the cation sublattice and high resistance to laser radiation. It have been established by calculations that boron can be incorporated into faces of oxygen tetrahedra of the LiNbO$_3$ crystal structure. Trace amounts of boron in the LiNbO$_{3}$ : B crystal structure suppress to a great extent the formation of Nb$_{\operatorname{Li}}$ point defects. At the same time, boron distorts significantly the oxygen framework of the LiNbO$_{3}$ crystal structure and thus changes the polarizability of oxygen octahedra, which determines the nonlinear optical properties of the crystal.