Analysis of the temperature-dependent infrared active lattice modes in the ordered phase of sodium nitrate

Abstract

The temperature dependence of the infrared reflectivity spectra of NaNO3 is reported in the whole ordered phase, from 10 to 549K. Reflectivity spectra from 5 to 600 cm-1, are fitted with a model of the factorised form of the dielectric function including the relaxation mode. The temperature dependence of the infrared active lattice mode frequencies, dampings and oscillator strengths is reported. The ionic effective charges are calculated from the TO-LO splitting of the polar modes. The temperature dependence of the relaxation parameters confirms the gradual phase transformation due to the growing of the disorder in the crystal structure above 423K.