Structural characterization of Cu2SnS3 and Cu2(Sn,Ge)S3 compounds

Cu2SnS3 (CTS) and Cu2Sn0.83Ge0.17S3 (CTGS) compounds were successfully prepared by a powder technology using a combination of mechanical alloying (MA) and spark plasma sintering (SPS). Structural, compositional and optical properties were studied. A true alloy with composition similar to the starting constituents was formed after 2 h of MA at 400 rpm. Subsequently, SPS was performed at 600 °C for 5 min under a pressure of 50 MPa. The Cu/(Sn + Ge) composition ratios of the MA and SPS materials, determined by wavelength dispersive X-ray spectroscopy, are in the range of 1.84-1.94. Rietveld refinements of the powder X-ray diffraction data show a good agreement with the monoclinic crystal structure already for the MA materials. No structural changes were observed after SPS. Raman measurements coincide with XRD results in the identification of the characteristic peaks from phonon vibrational modes of monoclinic CTS phase. Band gaps between 1.24 eV and 1.34 eV were determined by diffuse reflectance for the mechanically alloyed and sintered samples.