Raman studies of the FE-AFE phase transition in ceramic Li _0.12Na_0.88Ta_0.2Nb_0.8O ₃solid solution

The ferroelectric to antiferroelectric phase transition at 350C in ceramic Li 0.12 Na 0.88 -Ta 0.2 Nb 0.8 O 3 solid solution is studied by Raman spectroscopy. As the temperature of the solid solution sample is raised, considerable broadening of translational vibration bands of cations in the octahedral and cubo-octahedral cavities and of vibration bands of the oxygen carcass is observed. Intensity of Raman band corresponding to bridge valent vibrations (BVV) of oxygens decreases to zero. The ferroelectricity of the solid solution is shown to be lost mainly because of the growing anharmonicity of vibrations of the cavity cations.