Order-disorder nature of ferroelectric phase transition in stoichiometric LiNbO₃ Crystals

Abstract

In order to study the nature of a ferroelectric phase transition of LiNbO₃, the A₁(z) symmetry optical modes were investigated by Raman spectroscopy. The marked difference among stoichiometric and off-stoichiometric crystals was observed in their damping factors at 90 K. The asymmetric phonon peaks in the spectra were analyzed by taking account the anharmonicity of the interatomic potential. The temperature dependence of phonon frequency and damping was determined using the fitting by a superposition of multi-Lorentzians. The lowest mode frequency does not display the marked softening, while the damping factor increases gradually upon heating, in stoichiometric crystals. The validity of the order-disorder nature was examined for the ferroelectric phase transition

Key Words:

• lithium niohate
• Raman
• optic phonon
• order-disorder