Synthesis and characterization of new multinary selenides Sn₄In₅Sb₉Se₂₅ and Sn_6.13Pb_1.87In_5.00Sb_10.12Bi_2.88Se₃₅

Multinary selenides, Sn₄In₅Sb₉Se₂₅ (1) and Sn_6.13Pb_1.87In_5.00Sb_10.12Bi_2.88Se₃₅ (2) were synthesized by solid-state sintering reactions. These compounds were initially observed resulting from the exploratory synthesis of multinary selenides in In–Sn–Sb–Se systems. Sn₄In₅Sb₉Se₂₅ crystallizes in a monoclinic lattice with a ​= ​31.820(2) Å, b ​= ​4.0241(3) Å, c ​= ​19.703(2) Å, β ​= ​114.246(5)°, and V ​= ​2300.4(3) ų; space group C2/m (No. 12); Z ​= ​2. Sn_6.13Pb_1.87In_5.00Sb_10.12Bi_2.88Se₃₅ crystallizes in a monoclinic lattice with a ​= ​31.6883(5) Å, b ​= ​4.0709(1) Å, c ​= ​26.5406(4) Å, β ​= ​105.710(1)°, and V ​= ​3295.8(2) ų; C2/m (No. 12); Z ​= ​2. The structures of both compounds are constructed with two building units of NaCl¹⁰⁰-type [M_2x−4²⁺M₄³⁺Se_2x+2]∞1 and NaCl¹¹¹-type [M_2y−2³⁺Se_3y−3]∞2. The structural anisotropy leads to a columnar or layered shape and strongly preferred orientation along [010] direction upon two compounds. These materials exhibit black color comprising a semiconducting property. Band gaps observed in electrical conductivity measurements are 0.66 ​eV and 0.62 ​eV for compound 1 and 2, respectively. UV–vis–NIR spectroscopy and the electronic band structure calculations at the density functional theory (DFT) level indicate the results of the semiconducting behaviors. Measurements of Seebeck coefficient indicates p-type semiconductors for both compounds.