Pressure-induced phase transitions of ZnSe under different pressure environments

The structural, vibrational and electronic properties of ZnSe under different pressure environments up to ∼40.0 GPa were investigated using a diamond anvil cell in conjunction with ac impedance spectroscopy, Raman spectroscopy and high–resolution transmission electron microscopy. Under the non–hydrostatic condition, ZnSe exhibited a structural phase transition from a zinc–blende to a cinnabar structure at ∼4.9 GPa, indicated by the obvious splitting of the transverse optical mode in the Raman spectra and a noticeable variation in the slope of the electrical conductivity. With increasing pressure, metallization appeared at ∼12.5 GPa, which was characterized by the high–pressure Raman spectroscopy and temperature–dependent electrical conductivity results. When the pressure was increased up to ∼30.0 GPa, another phase transition was identified by the appearance of a new peak in the Raman spectra. Compared to the non–hydrostatic condition, a roughly 2.0 GPa delay of transition pressure for ZnSe was observed at the hydrostatic condition. However, the structural phase transformation was found to be irreversible only under the non–hydrostatic condition. The unique properties displayed by ZnSe under different pressure environments may be attributed to the constrained interlayer interaction owing to the presence of the pressure medium.