In situ study of the crystallization in GeTe0.26 Se0.74 thick film by synchrotron X-ray diffraction

Crystallization in unencapsulated GeTe(0.2)6Se(0.74) amorphous 3 mu m-thick films produced by thermal co-evaporation technique was studied by in situ temperature-dependent synchrotron powder X-ray diffraction from room temperature up to 418 degrees C and back to 30 degrees C. The experimental results obtained with a continuous heating rate of 2 degrees C/min under a protective nitrogen atmosphere showed that the crystallization process took place in several steps i) total crystallization of the amorphous phase to an intermediate crystallized phase, (ii) total transformation of the intermediate phase to a second crystallized phase. The intermediate phase corresponds to a solid solution with a metastable alpha-GeTe-like rhombohedral polar structure (R3m) presenting a uniaxial negative thermal ex-pansion along the c-axis. The onset of crystallization to the polar structure is around 270 degrees C. The high-temperature phase has a stable hexagonal structure with a P6(3)mc space group. When cooling, until back to room temperature, the hexagonal structure is conserved. The effect of a changing heating rate from 2 degrees to 0.1 degrees C/min was also investigated. In this context, the crystallization scheme is modified. (c) 2023 Elsevier B.V. All rights reserved.