Synthesis, structure, and properties of EuScCuS3 and SrScCuS3

The crystal structures of the first-synthesized compound EuScCuS 3 and previously known SrScCuS 3 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 KZrCuS 3 , with a ​= ​3.83413(3) Å, b ​= ​12.8625(1) Å, c ​= ​9.72654(8) Å (SrScCuS 3 ) and a ​= ​3.83066(8) Å, b ​= ​12.7721(3) Å, c ​= ​9.7297(2) Å (EuScCuS 3 ). The temperatures and enthalpies of incongruent melting are the following: Т m ​= ​1524.5 К, ΔH m ​= ​21.6 ​kJ•mol −1 (SrScCuS 3 ), and Т m ​= ​1531.6 К, ΔH m ​= ​26.1 ​kJ•mol −1 (EuScCuS 3 ). 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. EuScCuS 3 manifests a ferromagnetic transition at 6.4 ​K. The SrScCuS 3 compound is diamagnetic. The optical band gaps were found to be 1.63 ​eV (EuScCuS 3 ) and 2.24 ​eV (SrScCuS 3 ) from the diffuse reflectance spectra. The latter value is in good agreement with that calculated by the DFT method. The narrower band gap of EuScCuS 3 is explained by the presence of 4f-5d transition in Eu 2+ 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 AScCuS 3 (A ​= ​Sr, Eu). • The AScCuS 3 (A ​= ​Sr, Eu) compounds are mid-gap, indirect-bandgap semiconductors. • The EuScCuS 3 compound exhibits ferromagnetic properties at low temperature, and SrScCuS 3 is a diamagnetic. • The compound EuScCuS 3 is more stable in the inert atmosphere than SrScCuS 3 , and both melt incongruently. • The ab initio calculations of the Raman and infrared spectra of AScCuS 3 (A ​= ​Sr, Eu) agree well with experiment.