Cs 2 Ln 3 CuS 8 (Ln = La-Nd, Sm-Tb): Synthesis, Crystal Structure, and Magnetic and Optical Properties

This work reports the preparation of new quaternary sulfides Cs Ln CuS (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 Ln S (EuS), Cs S , Cu S, 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 ACe CuS series (A = Cs, K) and that of K CeCu S . 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 Cs Gd CuS 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.