Analysis of the temperature-dependent lattice modes in sodium nitrite by infrared spectroscopy

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Abstract
The temperature dependence of the infrared reflectivity spectra of NaNO2 is reported for the ferroelectric and paraelectric phases, over a wide temperature range (10-500K). Reflectivity spectra from 5 to 600 cm-1 have been fitted with a model of the factorised form of the dielectric function including the relaxational mode. The temperature dependence of the lattice mode frequencies, damping factors and oscillator strengths in the two phases is reported. The ionic effective charges are calculated from the TO-LO splitting of the polar modes. The study confirms the activity of five lattice modes in the ferroelectric and paraelectric phases and shows the existence of dielectric relaxation in the low-frequency region consistent with the order-disorder nature of the phase transition.