Crystal and electronic structures and physical properties of two semiconductors: Pb4Sb6Se13 and Pb6Sb6Se17

The title compounds were synthesized by directly reacting the elements in stoichiometric ratios at elevated temperatures. Their crystal structures were determined by single crystal X-ray diffraction. Pb4Sb6Se13 crystallizes in the monoclinic space group I2/m with lattice dimensions of a=24.591(1) Å, b=4.0910(2) Å, c=25.212(1) Å, β=93.943(1)°, V=2530.3(2) Å3 (Z=4), while Pb6Sb6Se17 crystallizes in the orthorhombic space group P21212 with lattice dimensions of a=15.872(4) Å, b=24.061(7) Å, c=4.1382(9) Å, V=1580.4(7) Å3 (Z=2). Electronic structure calculations predicted semiconducting behavior. Temperature dependent electrical conductivity measurements verified this prediction for Pb4Sb6Se13.