Pressure-dependent Raman spectra of Cu2GeS3 and Cu2SnS3

Cu₂GeS₃ and Cu₂SnS₃ crystalline samples with monoclinic (space group Cc) structures were fabricated using Bridgman method. The lattice constants, determined from the powder X-ray diffraction pattern, were a = 6.44 Å, b = 11.30 Å, c = 6.42 Å, and β = 108.44° for Cu₂GeS₃ and a = 6.65 Å, b = 11.57 Å, c = 6.66 Å, and β = 109.30° for Cu₂SnS₃. Cu₂GeS₃ exhibited eight Raman-active vibration modes at 255 cm⁻¹, 281 cm⁻¹, 299 cm⁻¹, 317 cm⁻¹, 339 cm⁻¹, 359 cm⁻¹, 397 cm⁻¹, and 422 cm⁻¹, while Cu₂SnS₃ showed only four modes at 294 cm⁻¹, 316 cm⁻¹, 354 cm⁻¹, and 374 cm⁻¹ at ambient conditions. The Raman spectra were also measured at pressures up to 5.31 GPa, and the effects of high pressure on the observed Raman modes were discussed.