Semiconductor-to-semimetal transition on Te doping in a new semiconducting material BaPbSbSe.

Semiconducting antimony-containing chalcogenides are an emerging class of materials for their applications in the thermoelectric and optoelectronic fields. A series of new polycrystalline antimony-containing chalcogenides BaPbSbSeTe ( = 0 to 4) have been prepared by heating the elements at 1073 K. The parent monoclinic selenide, BaPbSbSe, adopts the 2/ space group, as determined by a single-crystal X-ray diffraction study. The selenide structure consists of 2∞[PbSbSe] layers in which Pb and Sb sites are disordered. The PXRD studies show that a maximum of 40% of Se atoms in the BaPbSbSe structure can be substituted by Te atoms. The refined unit cell volume of the polycrystalline BaPbSbSeTe increases almost linearly with values following Vegard's law. Optical bandgap measurements indicate the semiconducting nature of the = 0, 1, and 2 samples, whereas no bandgap transition was found for the = 3 and 4 compositions. BaPbSbSe exhibits an ultra-low thermal conductivity () of ∼0.24 W m K at 773 K. The substitution of the Te atoms at the Se sites of the BaPbSbSe structure significantly improves electrical conductivity values. The = 3 and 4 compositions of the BaPbSbSeTe series show the semimetal-like temperature dependence of electrical conductivity. The T value of the = 2 composition is almost zero at 773 K due to its poor electrical conductivity. A further increase in Te concentration in BaPbSbSeTe leads to an enhancement of the T value (= 0.09 for = 4) at 773 K.