Far-Infrared investigation of the structural phase transitions of some two-dimensional layer compounds

Abstract

The far-infrared spectra of the layer structure compounds of the type (C _n H_2n+1NH₃)₂MCl₄, n = 1, 2, 3,…, M = Cu, Cd, have been measured in the region of 10–400 cm⁻¹ as a function of the temperature between 1 and 300 K. The rather involved spectra of the compounds investigated are due to the normal lattice modes of the layers alone. The changes of the spectra with temperature can be interpreted in terms of the structural phase transitions which these compounds show in this temperature region. There is an indication for the presence of a soft mode of the two-dimensional layer.