Abstract

Four quaternary sulfides SrCu2MS4 and EuCu2MS4 (M=Ge and Sn) were prepared from a thoroughly ground mixture of EuS or SrS, Cu, or Sn, and S in stoichiometric proportions. Electrical conductivity measurements on pressed pellets showed that all the phases are semiconductors. The optical band gaps were assessed at 2.8eV for SrCu2GeS4, 2.1eV for SrCu2SnS4, 2.2eV for EuCu2SnS4, and 1.6eV for EuCu2GeS4. Both Sr-based compounds present a temperature-independent paramagnetism, of about +135×10-6 and +92×10-6emu/mol, for SrCu2SnS4 and SrCu2GeS4, respectively. In the case of the europium compounds, they follow a Curie-Weiss dependence above 1.8K (EuCu2GeS4) and above 4K (for EuCu2SnS4), with values of the magnetic effective moment ?eff and the Curie-Weiss temperature ?, equal to 6.27?B and -2.8K for EuCu2GeS4, and 6.81?B and +0.7K, for EuCu2SnS4. The experimental magnetic moments confirm that the europium ion is in divalent state, similar to Sr in the related compounds. © 2003 Elsevier Science (USA). All rights reserved.