FAR INFRARED INVESTIGATION OF THE DIELECTRIC FUNCTION OF KNO3 BY ASYMMETRIC FOURIER SPECTROSCOPY

Spectra of the complex amplitude reflection coefficient of KNO3 single crystals were measured for all phases between room temperature and 190 degrees C in the spectral region from 15 to 300 cm-1 by asymmetric Fourier spectroscopy. The complex dielectric function epsilon ( omega ,T) was evaluated from these data. In the room temperature phase II (aragonite structure) the epsilon -spectra correspond to damped classical dispersion oscillators. In the disordered phase I T>128 degrees C, the picture of a relaxation type process coupled to an oscillator gives a good qualitative description of the spectra. The details of the spectra and their change in the transition to the ferroelectric phase III are consistent with Shinnaka's model (1962) of the structure of phase I.