CsLnCuS (Ln = La-Nd, Sm-Tb): Synthesis, Crystal Structure, and Magnetic and Optical Properties.

This work reports the preparation of new quaternary sulfides CsLnCuS (Ln = La-Nd, Sm-Tb), their original crystal and electronic structures, and their magnetic properties. The sulfides were prepared using a reactive flux method from mixtures of LnS (EuS), CsS, CuS, and S. They crystallize in a new type of structure (2/ space group) and exhibit a layer-like crystal structure, which is a hybrid of those of the ACeCuS series (A = Cs, K) and that of KCeCuS. The values of the optical band gap calculated by the Kubelka-Munk equation are in the range of 1.2-2.62 eV depending on the nature of the Ln ion. The CsGdCuS compound displays relatively great magnetic refrigerating properties at cryogenic temperature with the mass entropy change (-Δ) reaching 19.5 J kg K at 3.5 K for Δ = 5 T.