Temperature-induced phase transition dynamics in large-sized GeTe single crystals: Multimodal insights from XRD and Raman spectroscopy

GeTe has garnered significant attention in the field of phase-change memory devices due to its exceptional electrical transport properties and unique thermal response behavior. However, the temperature-induced phase transition mechanisms in large-sized GeTe single crystals remain insufficiently understood. In this work, high-quality centimeter-scale GeTe single crystals were successfully synthesized. Variable-temperature X-ray diffraction shows the merging of the diffraction peaks began at 600 K. The peaks at 24.9°(003) and 26.0°◦(101) gradually merge into the (111) peak at 25.7°. Other peaks at 41.9°(104) and 43.3°(110) gradually merge into the (220) peak at 42.6°. These phenomena collectively indicate GeTe's phase transition from rhombohedral to cubic phase. The change of the A_g² and A_g³ Raman mode, indicate a structural transition of GeTe in the 600–660 K temperature range. All modes exhibit strong polarization dependence under cross-polarized configurations. Notably, the depolarization ratio serves as a quantitative indicator to accurately reveal the phase transition evolution and symmetry characteristics of GeTe. Finally, the first-principles calculations were employed to analyze the internal electronic structure changes. These calculations provided robust evidence for the superior properties of GeTe. This research contributes to a deeper understanding of temperature-driven phase transition mechanisms in large-sized GeTe single crystals.