Condensed Matter Seminars

Bi-Sb alloys have shown promising thermoelectric (TE) properties at cryogenic temperature (<200 K). Over six decades, the figure of merit zT of n-type polycrystalline Bi-Sb has plateaued at ~0.4, while its p-type counterpart has remained even lower at ~0.1. We have studied the TE properties of melt-spun and spark plasma sintered (SPS) Bi-Sb alloys. We obtained a zT of 0.55 @100-150 K for n-type undoped Bi₈₅Sb₁₅ based on a low thermal conductivity 1.5 W/(m*K) measured with the hot-disk method. For p-type Bi-Sb, doping effects of Ge, Sn, and Pb were investigated. A high doping level of Ge and a high doping efficiency of Pb were obtained with the help of a low-temperature SPS processing. The transport properties (resistivity and Seebeck coefficient) of n-type undoped and p-type doped Bi₈₅Sb₁₅ were analyzed using the two-band effective mass model within the Boltzmann transport theory. A band gap decreasing phenomenon was observed which poses challenges to the improvement of p-type Bi-Sb’s zT.