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 2 Ln 3 CuS 8 (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 2 S 3 (EuS), Cs 2 S 6 , Cu 2 S, and S. They crystallize in a new type of structure ( C 2/ m space group) and exhibit a layer-like crystal structure, which is a hybrid of those of the ACe 2 CuS 6 series (A = Cs, K) and that of K 2 CeCu 2 S 4 . 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 2 Gd 3 CuS 8 compound displays relatively great magnetic refrigerating properties at cryogenic temperature with the mass entropy change (-Δ S M ) reaching 19.5 J kg -1 K -1 at 3.5 K for Δ H = 5 T.