In situ thermo-Raman spectroscopy and ab initio vibrational assignment calculations of cubanite CuFe2S3

In situ thermo-Raman spectroscopy is used to study a single crystal of natural orthorhombic cubanite from the Talnakh copper-nickel sulfide deposit (Norilsk, Russia). The dependence of the wavenumbers and FWHMs of vibrational modes on temperature, including the cubanite -> isocubanite phase transition region, is studied in the range of 83-873 K. For the first time, the polarized Raman spectra of cubanite have been interpreted according to ab initio calculations performed using the density functional theory (DFT) implemented in the VASP package. In spite of the tetrahedral environment of Cu and Fe atoms in cubanite, the spectra demonstrate the presence of different types of bending (twisting, wagging, scissoring, etc.) and stretching vibrations in two different triatomic (S2-Cu-S2) and (Fe-S1-Fe) fragments for A(g) and B-2g symmetries, and in three- and four-atomic (S1-Cu-S1) and FeS(2)(3) fragments, respectively, for B-1g and B-3g symmetries.