Synthesis, structure, melting and optical properties of three complex orthorhombic sulfides BaDyCuS3, BaHoCuS3 and BaYbCuS3
Complex sulfides BaDyCuS3, BaHoCuS3 and BaYbCuS3 were synthesized in a flow of sulfiding gases (CS2, H2S) at 900оC from standard solutions of lanthanide and copper nitrates, as well as from the same standard Ba(OH)2 solution. The crystal structures of BaDyCuS3, BaHoCuS3 and BaYbCuS3 were obtained by the Rietveld refinement method. All three compounds crystallize in the Cmcm space group (KZrCuS3 structural type) as predicted by the tolerance factor analysis. Their micromorphological, thermal and spectroscopic properties are evaluated. BaDyCuS3 and BaHoCuS3 melt congruently at 1376.5 °C and 1363.8 °C. BaYbCuS3 melts incongruently at 1353.3 °C. The optical band gap is 2.45 eV for BaDyCuS3, 2.37 eV for BaHoCuS3 and 1.82 eV for BaYbCuS3. The low bandgap of BaYbCuS3 is explained by the charge transfer band of Yb at the bottom of conduction band. The vibrational parameters of BaDyCuS3, BaHoCuS3 and BaYbCuS3 crystals were determined with the use of Raman and Infrared spectroscopies.