Temperature-Dependent Vibrational Modes in Sodium Nitrite

Abstract

The reflectivity of single-crystal sodium nitrite has been measured as a function of temperature and crystallographic orientation over a wavelength region which spans all the eight infrared-active normal modes. The temperature-dependent dielectric response functions and oscillator parameters have been obtained both by a Kramers-Kronig analysis and by fitting the reflectivity data with a series of independent harmonic oscillators. The latter model produces a good fit to the observed reflectivity at all temperatures both above and below the phase transition. Although all observed modes are temperature-dependent, none is thought to be a ferroelectric soft mode.