Pressure induced semimetal-to-metal transition and new structure of Ta2NiSe5above 10 GPa.

Previous studies of the transition metal chalcogenide Ta₂NiSe₅has identified two phase transitions occurring between 0-10 GPa, involving the excitonic insulator-to-semiconductor transition at 1 GPa and the semiconductor-to-semimetal transition at 3 GPa. However, there is still a lack of in-depth research on the changes in its physical properties changes above 10 GPa. In this study, Ta₂NiSe₅were investigated under high-pressure conditions using high-pressure x-ray diffraction and high-pressure x-ray absorption experiments. During the experimental process, a novel phase transition from the semimetal to the metal phase was observed between 10-60 GPa, specifically between 10-14 GPa, and the structure of the new phase was determined to be P2₁/m through first-principles calculations. This transition mechanism is attributed to the sliding of the weakly coupled layers of Ta₂NiSe₅within thea-cplane, leading to changes in the crystal lattice constants and symmetry. This research fills a gap in the understanding of Ta₂NiSe₅'s crystal structure under high pressure and contributes to the broader field of transition metal chalcogenides.