KCaEr2CuS5:: A new pentanary rare-earth layered chalcogenide without substitutional disorder

A new pentanary rare-earth chalcogenide without substitutional disorder, KCaEr2CuS5, was obtained from reaction of the Er-Ca-Cu-S precursor with KBr flux by either a two-step flux method or a direct reaction of the mixture of the binary components (1Cu(2)S: 2Er(2)S(3): 3CaS) with excess KBr as flux. KCaEr2CuS5 crystallizes in the orthorhombic space group Cmcm(No. 63) with a = 3.9327(5) angstrom, b = 13.410(2)angstrom, c = 17.042(2) angstrom, V = 898.8(3) angstrom(3), Z = 4, R = 0.0632, and R-w = 0.0627. The KCaEr2CuS5 structure consists of four different building units: ErS6 octahedra, CaS6 octahedra, CuS4 tetrahedra, and KS6 trigonal prisms; it is characterized by (2)(infinity)[Er2CuS5](3-) layers that are formed by the interconnection of double ErS6 octahedral chains with CuS4 tetrahedral chains in the a-c plane. K+ and Ca2+ cations are located in the cavities defined by S2- anions between the (2)(infinity)[Er2CuS5](3-) layers. KCaEr2CuS5 is a semiconductor with an estimated band gap of 2.4 eV and shows a Curie-Weiss paramagnetic behavior in the 5-300 K range.