Temperature and Pressure Dependence of Raman Scattering in Amorphous GeS2

Abstract

The evolution of the Raman spectrum of amorphous GeS2 is reported over wide temperature (300 to 1075 K) and pressure (0 to 10.8 GPa) ranges. The temperature dependence shows that a-GeS2 turns gradually crystalline above Tg, first to the 3D-phase and then to the layered (2D)-phase, with the latter one being retained up to the melting point and upon normal cooling to 300 K. The evolution of the Ac1 companion band of a-GeS2 into the crystalline phases indicates that this band is due to the symmetric stretch of S atoms in bridges of edge-sharing Ge(S1/2)4 tetrahedra. The Raman bands of a-GeS2 harden with increasing pressure, indicating a continuous decrease of the Ge–S bond length, while the material remains amorphous throughout the pressure range. Above 10 GPa, the material becomes almost opaque, thus making difficult the observation of Raman scattering. All these pressure induced effects are reversible after bringing the sample to ambient pressure.