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.

Oriented thin sections parallel to (001) and (010) were also measured to 110 K as a function of the direction of the electric vector E, but could not be unambiguously interpreted.

Though the effect is very slight it is tentatively proposed that the phase transition (already characterized by calorimetry and lattice parameters) involves changes in K-O and T-O-T bonds.