Synthesis, structure, melting and optical properties of three complex orthorhombic sulfides BaDyCuS3, BaHoCuS3 and BaYbCuS3

• Ternary sulfides BaPrCuS 3 and BaSmCuS 3 are first synthesized by the sulphidation reaction. • The BaPrCuS 3 and BaSmCuS 3 compounds crystallized in space groups Pnma and Cmcm , respectively. • The vibrational parameters of BaPrCuS 3 and BaSmCuS 3 are comparatively observed by Raman spectroscopy . Complex sulfides BaDyCuS 3 , BaHoCuS 3 and BaYbCuS 3 were synthesized in a flow of sulfiding gases (CS 2 , H 2 S) at 900 о C from standard solutions of lanthanide and copper nitrates, as well as from the same standard Ba(OH) 2 solution. The crystal structures of BaDyCuS 3 , BaHoCuS 3 and BaYbCuS 3 were obtained by the Rietveld refinement method. All three compounds crystallize in the Cmcm space group (KZrCuS 3 structural type) as predicted by the tolerance factor analysis. Their micromorphological, thermal and spectroscopic properties are evaluated. BaDyCuS 3 and BaHoCuS 3 melt congruently at 1376.5 °C and 1363.8 °C. BaYbCuS 3 melts incongruently at 1353.3 °C. The optical band gap is 2.45 eV for BaDyCuS 3 , 2.37 eV for BaHoCuS 3 and 1.82 eV for BaYbCuS 3 . The low bandgap of BaYbCuS 3 is explained by the charge transfer band of Yb at the bottom of conduction band. The vibrational parameters of BaDyCuS 3 , BaHoCuS 3 and BaYbCuS 3 crystals were determined with the use of Raman and Infrared spectroscopies.