Structural dimension modulation in a new oxysulfide system of Ae2Sb2O2S3 (Ae = Ca and Ba)

Abstract

Inspired by the abundant structural diversity and potential applications of Sb-based oxysulfides, two new compounds with the same stoichiometry, Ae₂Sb₂O₂S₃ (Ae = Ca, Ba), were successfully synthesized via solid state reactions. Both crystallize in the C2/c space group (no. 15) of a monoclinic system, however, possess different structural dimensions induced by different sizes of template alkaline-earth ions. Ca₂Sb₂O₂S₃ is composed of one-dimensional anionic [Sb₂O₂S₃]⁴⁻ chains isolated by Ca²⁺ ions, while Ba₂Sb₂O₂S₃ consists of zero-dimensional anionic [Sb₂O₂S₃]⁴⁻ clusters separated by Ba²⁺ ions. Higher structural dimension endows the 1D Ca₂Sb₂O₂S₃ with a higher melting point (m.p. = 720 °C) and a narrower band gap (E_g = 2.36 eV), compared with the m.p. = 692 °C and E_g = 2.78 eV of Ba₂Sb₂O₂S₃. Both exhibit interesting photoluminescence properties with multiemission characteristics. DFT calculations reveal that the band edges of Ae₂Sb₂O₂S₃ are mainly composed of Sb−S bond orbitals, while O 2p orbitals also contribute to the valence band maximum of Ba₂Sb₂O₂S₃.