Synthesis and Crystal Structure of a New Quaternary Thioantimonate, Na_9Gd_5Sb_8S_26

摘要

The first Na-containing quaternary rare-earth thioantimonate, Na_9Gd_5Sb_S_26, was synthesized from the reaction of Gd metal, Sb, and S in Na_2S flux at 750 deg C. Black plate-shaped crystals were obtained and their crystal structure was determined by the single-crystal X-ray diffraction method. This compound crystallizes in the orthorhombic space group Pnma (No. 62) with a unit cell of a = 11.406(3) A, b = 23.765(2) A, c = 16.923(5) A, and Z = 4. Na_9Gd_5Sb_8S_26 has a complex three-dimensional structure that consists of SbS_3, SbS_4, GdS_6, and GdS_7 units. In the structure, three crystallographically different Gd atoms form a staircase-shapoed building block, where two Gd atoms share disulfide ions, S_2~(2-). The formula of the compound can be described as (Na~+)_9(Gd~(3+))_5(Sb~(3+))_8(S~2-))_22(S_2(2-))_2. Measurement of the optically diffuse reflectance indicates that Na_9Gd_5Sb_S_26 is a semiconductor with a band gap of 1.63 eV.