Syntheses, structures, physical properties, and electronic structures of K Ln2CuS 4 ( Ln=Y, Nd, Sm, Tb, Ho) and K 2Ln4Cu 4S 9 ( Ln=Dy, Ho)

Abstract

Seven new quaternary metal sulfides, KY 2CuS 4, KNd 2CuS 4, KSm 2CuS 4, KTb 2CuS 4, KHo 2CuS 4, K 2Dy 4Cu 4S 9, and K 2Ho 4Cu 4S 9, were prepared by the reactive flux method. All crystallographic data were collected at 153 K. The isostructural compounds K Ln 2CuS 4 ( Ln=Y, Nd, Sm, Tb, Ho) crystallize in space group Cmcm of the orthorhombic system with four formula units in cells of dimensions ( Ln, a, b, c (Å)): Y, 3.9475(9), 13.345(3), 13.668(3); Nd, 4.0577(3), 13.7442(10), 13.9265(10); Sm, 4.0218(4), 13.6074(14), 13.8264(14); Tb, 3.9679(5), 13.4243(17), 13.7102(18); Ho, 3.9378(3), 13.3330(11), 13.6487(11). The corresponding R 1 indices for the refined structures are 0.0197, 0.0153, 0.0158, 0.0181, and 0.0178. The isostructural compounds K 2Dy 4Cu 4S 9 and K 2Ho 4Cu 4S 9 crystallize in space group C2/ m of the monoclinic system with two formula units in cells of dimensions ( Ln, a, b, c (Å), β (°)): Dy, 13.7061(13), 3.9482(4), 15.8111(15), 109.723(1); Ho, 13.6760(14), 3.9360(4), 15.7950 (16), 109.666(2). The corresponding R 1 indices are 0.0312 and 0.0207. Both structure types are closely related three-dimensional tunnel structures. The tunnels are filled with bicapped trigonal-prismatically coordinated K atoms. Their anionic frameworks are built from LnS 6 octahedra and CuS 4 tetrahedra. K Ln 2CuS 4 contains ∞ 1[CuS 3 5−] chains of vertex-sharing tetrahedra and K 2 Ln 4Cu 4S 9 contains ∞ 1[Cu 4S 8 12−] chains of tetrahedra. K 2Ho 4Cu 4S 9 shows Curie–Weiss paramagnetic behavior between 5 and 300 K, and has an effective magnetic moment of 10.71 μ B for Ho 3+ at 293 K. Optical band gaps of 2.17 eV for KSm 2CuS 4 and 2.43 eV for K 2Ho 4Cu 4S 9 were deduced from diffuse reflectance spectra. A first-principles calculation of the density of states and the frequency-dependent optical conductivity was performed on KSm 2CuS 4. The calculated band gap of 2.1 eV is in good agreement with the experimental value.