A CENTRAL PEAK AS A PRE-MELTING FEATURE IN NANO3 SPECTRA

The quasi-elastic and Raman spectra of NaNO3 are studied as a function of scattering configuration and temperature through the phase transition up to the close vicinity of the melting temperature. Results reveal the appearance of broad intense quasi-elastic scattering in the (ZZ) and (YX) spectra when the transition is approached from below. The slightly soft-phonon Eg lines detected in the (YZ) spectrum in the low-temperature phase are shown to persist above Tc. Neither the central peak, nor the phonon Eg modes seem to be connected with the transition to the high-temperature phase which is only partly disordered. Rather, the relaxational central peak is found to be related to the disordering process precursor of the melting.