Synthesis, crystal and electronic structure of the quaternary sulfides Ln2CuMS5 (Ln=La, Ce; M=Sb, Bi)

Abstract The series of quaternary sulfides with general formula Ln2CuMS5 (Ln=La, Ce; M=Sb, Bi) have been synthesized by solid-state reactions. Three representative members have been structurally characterized by single-crystal X-ray diffraction. La2CuSbS5 crystallizes in a new structure type (space group Ima2 (no. 46), Z=4, a=13.401(2)Å, b=7.592(1)Å, c=7.598(1)Å, V=773.1(3)Å3). The bismuth analogs of composition La2CuBiS5 and Ce2CuBiS5 crystallize with the La2CuInSe5 structure type (space group Pnma (no. 62), Z=4). Lattice parameters for La2CuBiS5: a=11.9213(5)Å, b=3.9967(2)Å, c=17.0537(8)Å, V=812.56(7)Å3; lattice parameters for Ce2CuBiS5: a=11.9179(15)Å, b=3.9596(5)Å, c=16.955(2)Å, V=800.13(17)Å3). The similarities and the differences between the two structures are discussed. Electronic structure calculations for La2CuSbS5 and La2CuBiS5 are also presented; they suggest semiconducting behavior with energy gaps exceeding 1.7eV