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

摘要

To date, the high-temperature phase transition R3m-Fm (3) over barm 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.