Polymorphic transformation from metastable β to stable α phase in MnTe flake

Abstract A manganese telluride (MnTe) is an intriguing polymorphic semiconductor. Among them, the metastable β-MnTe phase, characterized by a wurtzite-type structure, has been successfully fabricated as a sputtered film on substrates. However, the bulk or free-standing β-MnTe without substrates has never been realized. In this study, we fabricated a β-MnTe flake through a lift-off process. Notably, the X-ray diffraction patterns of the flake sample approached the predicted peak positions of bulk β-MnTe, indicating strain relaxation. This represents the pioneering experimental success to demonstrate a bulk-like β-MnTe. Furthermore, we conducted thermal analyses associated with the β→α transformation through differential scanning calorimetry. The β-MnTe flake exhibited a lower transformation temperature than films, suggesting diminished thermal stability of the β phase. The enthalpy change was quantitatively determined as −45.1 kJ mol -1 , which arises from the substantial volume change. These experimental demonstrations contribute to utilizing free-standing β-MnTe in optoelectronic and piezoelectric fields.