Isothermal phase behavior of Ag3SbS3, ZnGeP2, and ZnS

The isothermal phase behaviors of Ag3SbS3, ZnGeP2, and ZnS have been determined as a function of pressure at room temperature. Phase transformations were observed optically for each material in a diamond anvil cell with single crystals at pressures of (4.9±0.15) GPa, (20±5) GPa, and (15.0±0.2) GPa, respectively. ZnGeP2 also transformed to a second high-pressure phase at approximately 32 GPa. Under hydrostatic pressure zinc sulfide showed no transformation between the wurtzite and sphalerite forms. The pressure-volume relations were measured in the diamond anvil pressure cell by the energy dispersive X-ray diffraction method. The resulting data were analyzed for each low-pressure phase in terms of model equations of state, including the Birch, Birch-Murnaghan, Murnaghan, and Tait equations. The isothermal bulk modulus, B, was determined in each case with the estimated values being: 80 GPa for ZnS (wurtzite); 67 GPa for ZnS (sphalerite); 28 GPa for Ag3SbS3; and 79 GPa for ZnGeP2. Estimates were also made for the pressure derivative, (dB/dP), at zero pressure, with the values being: 3.7, 4.8, 5.6, and 3.2, respectively.