Brillouin Scattering Study on KNO3 Crystal: Appearance of Intermediate Phase on Heating.

The structural phase transition of potassium nitrate, KNO 3, has been investigated by means of Brillouin scattering. With increasing temperature, a previously unreported change in other experiments was observed in Brillouin shift, linewidth and mode number, which varied for many measurements. It appears that a phase other than the α- and β-phases, called the intermediate phase, appeared between these two phases. This phase always started to appear at 128°C, but did not disappear at a fixed temperature for any measurement. This behavior is similar to that of the γ-phase. We have discussed the origin and nature of the intermediate phase.