Pressure-induced phase transformations in the chalcopyrite-structure compounds: CuGaS₂ and AgGaS₂

Abstract

Pressure-induced phase transformations have been found in CuGaS₂ and AgGaS₂ by high-pressure x-ray-diffraction studies, using the energy dispersion technique. CuGaS₂ transforms from the chalcopyrite to the NaCl type near 16 GPa. AgGaS₂ undergoes three pressure-induced phase changes: (1) from chalcopyrite to a hexagonal lattice near 5 GPa, (2) from chalcopyrite and hexagonal to α-NaFeO₂ type near 12 GPa, and (3) to the NaCl type at pressures above 15 GPa. These results confirm the pressure-induced phase transitions indicated by the phonon behavior in a recent high-pressure Raman study of CuGaS₂ and AgGaS₂. From the high-pressure x-ray data on the chalcopyrite phase, the following bulk modulus B₀ and dB₀/dP were obtained by fitting the data to the Murnaghan equation of state: CuGaS₂, B₀=96±10 GPa, B₀'=6.5; AgGaS₂, B₀=60#177;8 GPa, B₀'=6.