Synthesis, structure, and properties of EuScCuS3 and SrScCuS3

The crystal structures of the first-synthesized compound EuScCuS3 and previously known SrScCuS3 are refined by Rietveld analysis of X-ray powder diffraction data. The structures are found to belong to orthorhombic crystal system, space group Cmcm, structural type KZrCuS3, with a ​= ​3.83413(3) Å, b ​= ​12.8625(1) Å, c ​= ​9.72654(8) Å (SrScCuS3) and a ​= ​3.83066(8) Å, b ​= ​12.7721(3) Å, c ​= ​9.7297(2) Å (EuScCuS3). The temperatures and enthalpies of incongruent melting are the following: Тm ​= ​1524.5 К, ΔHm ​= ​21.6 ​kJ•mol−1 (SrScCuS3), and Тm ​= ​1531.6 К, ΔHm ​= ​26.1 ​kJ•mol−1 (EuScCuS3). Ab initio calculations of the crystal structure and phonon spectrum of the compounds were performed. The types and wavenumbers of fundamental modes were determined and the involvement of ions participating in the IR and Raman modes was assessed. The experimental IR and Raman spectra were interpreted. EuScCuS3 manifests a ferromagnetic transition at 6.4 ​K. The SrScCuS3 compound is diamagnetic. The optical band gaps were found to be 1.63 ​eV (EuScCuS3) and 2.24 ​eV (SrScCuS3) from the diffuse reflectance spectra. The latter value is in good agreement with that calculated by the DFT method. The narrower band gap of EuScCuS3 is explained by the presence of 4f-5d transition in Eu2+ ion that indicates a possibility to control the band gap of the chalcogenides by the inclusion of Eu. The activation energy of crystal structure defects, being the source of additional absorption in the NIR spectral range, was found to be 0.29 ​eV. Сomplex study of the crystal structure and properties of quaternary compounds AScCuS3 (A ​= ​Sr, Eu). [Display omitted] •The AScCuS3 (A ​= ​Sr, Eu) compounds are mid-gap, indirect-bandgap semiconductors.•The EuScCuS3 compound exhibits ferromagnetic properties at low temperature, and SrScCuS3 is a diamagnetic.•The compound EuScCuS3 is more stable in the inert atmosphere than SrScCuS3, and both melt incongruently.•The ab initio calculations of the Raman and infrared spectra of AScCuS3 (A ​= ​Sr, Eu) agree well with experiment.