Pressure-Induced Structural and Semiconductor-Metal-Superconductor Transitions in a High-Entropy van der Waals Compound (MnFeCuCdIn)PSe₃

The properties of the emerging phosphochalcogenide compounds can be tuned by temperature, pressure, and the chemical composition characterized by the compound entropy. However, it is unknown how the entropy of such a compound affects its structural stability and material properties when a state variable changes. In this work, a new layered high-entropy phosphoselenide compound (MnFeCuCdIn)PSe3 (denoted MPSe3) is prepared and its structural evolution and property changes are studied at pressures up to approximate to 60 GPa. It is found that the compound undergoes two isostructural changes at approximate to 10 and 20 GPa, a structural change forming a high-coordination phase in approximate to 32-35 GPa, a semiconductor-to-metal transition in approximate to 28-30 GPa at room temperature, and a metal-to-superconductor transition in approximate to 2.5-4.9 K at a pressure from approximate to 43 to 58 GPa. Combining data from prior studies, it is further found that for the MPSe3-type medium/high-entropy compounds, there exists a linear relationship between the structural transition pressure and the cation mixing entropy, and an inverse nearly linear relationship between the superconducting critical temperature and the cation mixing entropy, with the latter due primarily to the decrease in the Debye temperature. These findings will have great importance for developing new complex materials using the evolving entropy engineering.