Comparative investigation of LiNbO3 crystals Raman spectra in the temperature range 100–400 K

Abstract

We have investigated Raman spectra of congruent and stoichiometric LiNbO3 crystals in the temperature range 100–450 K. Slope gradient is greater for the temperature dependence of band width associated with Nb5+ ions vibrations than that associated with Li+ ions vibrations in a lithium niobate crystal structure. This fact indicates that the anharmonicity of Nb5+ ions vibrations along the polar axis is greater compared to Li+ ions vibrations. It is likely that O2– ions contribute to this anharmonicity. The O2– ions vibrations are characterized by an anharmonic potential in the LiNbO3 crystal structure. The O2– ions vibrations according to ab initio calculations strongly interact with vibrations of Nb5+ ions. We have found that the temperature dependence of the fundamental bands intensity is nonmonotonic and the “extra bands” intensity is strictly linear.