Synthesis and characterization of new multinary selenides Sn4In5Sb9Se25 and Sn6.13Pb1.87In5.00Sb10.12Bi2.88Se35

Multinary selenides, Sn4In5Sb9Se25 (1) and Sn6.13Pb1.87In5.00Sb10.12Bi2.88Se35 (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) angstrom, b = 4.0241(3) angstrom, c = 19.703(2) angstrom, beta = 114.246(5)degrees, and V = 2300.4(3) angstrom(3); space group C2/m (No. 12); Z = 2. Sn6.13Pb1.87In5.00Sb10.12Bi2.88Se35 crystallizes in a monoclinic lattice with a = 31.6883(5) angstrom, b = 4.0709(1) angstrom, c = 26.5406(4) angstrom, beta = 105.710(1)degrees, and V = 3295.8(2 )angstrom(3); C2/m (No. 12); Z = 2. The structures of both compounds are constructed with two building units of NaCl100-type(+)(+)[M2x-42+M43+Se2x+2] and NaCl111-type(+)(+)[M2y-23+Se3y-3]. 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.