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

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, bulk or free-standing β -MnTe without substrates has never been realized. In this study, we fabricated a β -MnTe flake using 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 study represents a pioneering experimental success in demonstrating 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 are expected to contribute to the application of free-standing β -MnTe in optoelectronic and piezoelectric fields.