Crystal structure and Raman scattering characterization of Cu2Fe1-xCoxSnS4 chalcogenide compounds

This work reports the synthesis by solid–state reaction of Cu₂Fe_1-xCo_xSnS₄ solid solutions. Crystal structures of Cu₂Fe_0.8Co_0.2SnS₄ and Cu₂Fe_0.6Co_0.4SnS₄ were investigated by single crystal X-ray diffraction. Both phases crystallize in the tetragonal stannite-type structure. The volume of the tetrahedral MS₄] (M = Fe, Co) presented the highest distortion, with Edge-Length Distortion (ELD) indices ～2% from the ideal tetrahedron. The powder X-ray diffraction (XRD) patterns of Cu₂Fe_1-xCo_xSnS₄ (x = 0.2, 0.4, 0.6 and 0.8) has been refined by Rietveld method. No secondary phases were detected in XRD patterns. An analysis of the vibrational properties of Cu₂Fe_1-xCo_xSnS₄ was performed using Raman scattering measurements. The Raman peaks were analyzed by fitting of the spectra and subsequently identifying the vibrational modes by comparison with experimental and theoretical data from Cu₂FeSnS₄ (CFTS) and Cu₂CoSnS₄ (CCTS) end-members. The spectra from Cu₂Fe_1-xCo_xSnS₄ show that there is a variation in the frequency of the main A₁ peak at ～320 cm^?1 together with a decrease in the secondary mode intensity at ～285 cm^?1. Full Width at Half Maximum (FWHM) and the intensity of the Raman peaks reflect the high crystallinity of Cu₂Fe_1-xCo_xSnS₄ solid solutions. The oxidation states of the metals were confirmed by temperature-dependent magnetization measurements performed in the antiferromagnetic Cu₂Fe_1-xCo_xSnS₄ solid solutions.