Synthesis and characterization of quaternary selenides Sn2Pb5Bi4Se13 and Sn8.65Pb0.35Bi4Se15

Quaternary selenides Sn2Pb5Bi4Se13 and Sn8.65Pb0.35Bi4Se15 were synthesized from the elements in sealed silica tubes; their crystal structures were determined by single-crystal and powder X-ray diffraction. Both compounds crystallize in monoclinic space group C2/m (No.12), with lattice parameters of Sn2Pb5Bi4Se13: a = 14.001(6) angstrom, b = 4.234(2) angstrom, c = 23.471(8) angstrom, V = 1376.2(1) angstrom(3), R-1/wR(2) = 0.0584/0.1477, and GOF = 1.023; Sn8.65Pb0.35Bi4Se15: a = 13.872(3) angstrom. b = 4.2021(8) (4) angstrom, c = 26.855(5) angstrom, V = 1557.1(5) angstrom(3), R-1/wR(2) = 0.0506/0.1227, and GOF = 1.425. These compounds exhibit tropochemical cell-twinning of NaCl-type structures with lillianite homologous series L(4, 5) and L(4, 7) for Sn2Pb5Bi4Se13 and Sn8.65Pb0.35Bi4Se15, respectively. Measurements of electrical conductivity indicate that these materials are semiconductors with narrow band gaps; Sn2Pb5Bi4Se13 is n-type, whereas Sn8.65Pb0.35Bi4Se15 is a p-type semiconductor with Seebeck coefficients -80(5) and 178(7) mu V/K at 300 K, respectively. (C) 2009 Elsevier Masson SAS. All rights reserved.