Anomalous temperature-induced volume contraction in GeTe

TL;DR

This study investigates the rhombohedral-to-cubic phase transition in GeTe, revealing an unexpected 0.6% volume contraction at the transition, supported by neutron diffraction experiments and phonon calculations.

Contribution

It provides detailed experimental data and theoretical insights into the anomalous volume contraction during GeTe's phase transition, which was not well understood before.

Findings

Observed 0.6% volume contraction at phase transition

Detailed temperature dependence of structural parameters

Supported experimental and theoretical analysis

Abstract

The recent surge of interest in phase change materials GeTe, Ge$_2$Sb$_2$Te$_5$, and related compounds motivated us to revisit the structural phase transition in GeTe in more details than was done before. Rhombohedral-to-cubic ferroelectric phase transition in GeTe has been studied by high resolution neutron powder diffraction on a spallation neutron source. We determined the temperature dependence of the structural parameters in a wide temperature range extending from 309 to 973 K. Results of our studies clearly show an anomalous volume contraction of 0.6\% at the phase transition from the rhombohedral to cubic phase. In order to better understand the phase transition and the associated anomalous volume decrease in GeTe we have performed phonon calculations based on the density functional theory. Results of the present investigations are also discussed with respect to the experimental data obtained for single crystals of GeTe.