A room-temperature phase transition in maximum microcline. Absorption in the far infrared (10?200 cm?1) in the temperature range 110?300 K

Abstract

The far infrared powder absorption spectra (10–200 cm−1) for a maximum microcline sample (obtained by ion-exchange from Amelia albite) and for a natural maximum microcline were measured at steps of 10 K on lowering and raising the temperature between 300 and 110 K. Of the absorption bands at 97.5, 113.5, 137.5, 148, and 157 cm−1 occurring at room temperature, those at 157 and eventually 148 cm−1 showed evidence of a phase transition and only that at 157 cm−1 showed hysteresis. The transition occurs at 245±5 K on lowering the temperature and the low-temperature form can be superheated to 300 K in the case of the ion-exchange sample.