Determination of stoichiometry, concentration of OH groups, and point defects in lithium niobate crystals from their IR absorption spectra

The concentration of OH impurity groups, the Li/Nb ratio, the concentration of Nb$_{Li}^{4+}$ and $V_{Li}^{-}$ point defects in stoichiometric and congruent LiNbO$_3$ crystals, as well as in crystals doped with magnesium and zinc at concentrations close to threshold concentrations, have been calculated from IR absorption spectra in the range of stretching vibrations of OH groups. The behavior of bands in the IR absorption spectra of heavily doped LiNbO$_3$ : Mg and LiNbO$_3$ : Zn crystals has been revealed to correlate with the behavior of the Raman spectrum line that corresponds to stretching bridge vibrations of oxygen atoms in the NbO$_6$ octahedron along the polar axis.