Concentration dependences of IR absorption spectra in the range of stretching vibrations of OH groups of congruent lithium-niobate crystals doped with zinc and magnesium

Abstract

The concentration behavior of the parameters of spectral lines that correspond to stretching vibrations of OH groups in the IR absorption spectra of LiNbO₃:Zn (0.04–4.46 mol % ZnO) and LiNbO₃:Mg (0.19–5.91 mol % MgO) crystals has been studied. It has been found that, in the range of threshold concentrations of Zn²⁺ and Mg²⁺ doping cations, the line parameters experience a jump. In this case, the widths of some lines decrease, which indicates the ordering of OH groups in the crystal. It has been shown that nonstoichiometric crystals are characterized by the occurrence of different positions of OH groups and different values of the quasi-elastic constants of O–H bonds in the crystal structure. In the stoichiometric LiNbO₃ crystal, all the positions of OH groups are the same, and the quasi-elastic constants of O–H bonds are identical.