Role of vacancies in the high-temperature pseudodisplacive phase transition in GeTe

Abstract

To date, the high-temperature phase transition R3m$\text{\ensuremath{-}}Fm\phantom{\rule{0.83328pt}{0ex}}\overline{3}\phantom{\rule{0.83328pt}{0ex}}m$ in GeTe is commonly believed to be second-order displacive with an anomalous volume contraction at the phase transition temperature, ${T}_{PT}$, from diffraction measurements. Three main results are here reported: (i) the phase transition is accompanied by latent heat absorption, (ii) in the high-resolution x-ray-diffraction powder pattern the cubic phase appears before the merging of the rhombohedral peaks, and (iii) the cubic phase possesses a larger amount of germanium vacancies than the rhombohedral phase. From results (i)--(iii) we conclude that the phase transition is not purely second-order displacive and that the volume contraction observed at ${T}_{PT}$ can be explained with the formation of vacancies in the cubic phase.