Manifestation of structural features of LiNbO:Zn and LiNbO:Mg crystals in their IR absorption spectra in the stretching region of OH groups.

Analysis of IR absorption spectra of LiNbO:Zn (0.04-4.46 mol % ZnO) and LiNbO:Mg (0.19-5.91 mol % MgO) single crystals in the stretching region of OH groups has been used to gain insight into composition-dependent structural changes in the crystals. The results demonstrate that, characteristically, the OH groups occupy different sites in the doped and congruent LiNbO crystals and have different quasielastic O-H bond constants in their structure. In stoichiometric lithium niobate crystals, all of the OH sites and quasi-elastic O-H bond constants are identical. At threshold Zn and Mg dopant concentrations, the frequencies, widths, and intensities of the observed lines change sharply. The linewidths in the spectra of the LiNbO:Zn crystals near their first concentration threshold (≈2.0 mol % ZnO) and the LiNbO:Mg crystals near their first and second concentration thresholds (≈3.0 and 5.5 mol % MgO) decrease markedly, indicating ordering of the position of the OH groups in the structure of the crystals. [ABSTRACT FROM AUTHOR]