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

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.