Enhanced thermoelectric properties of topological crystalline insulator PbSnTe nanowires grown by vapor transport

Bulk PbTe and alloy compounds thereof are well-known thermoelectric materials for electric power generation. Among these alloys, PbSnTe hosts unique topological surface states that may have improved thermoelectric properties. Here we report on the vapor-transport growth and thermoelectric study of high-quality single-crystalline PbTe and PbSnTe nanowires. The nanowires were grown along the < 001 > direction with dominant {100} facets; the chemical compositions of the wires depend strongly on the substrate position in the growth reactor. We measured the thermopower and electrical and thermal conductivities of individual nanowires to determine the thermoelectric figure of merit ZT. Compared to bulk samples, the PbSnTe nanowires showed both improved thermopower and suppressed thermal conductivity, enhancing the ZTs to ~0.018 and ~0.035 at room temperature. The enhanced thermopower may result from the unique topological surface states; the suppression of thermal conductivity may relate to increased phonon-surface scattering. Compared to PbTe nanowires, the PbSnTe wires have lower thermopower but significantly higher electrical conductivities. This study highlights nanostructuring in combination with alloying as an important approach to enhancing the figure of merit ZT of thermoelectric materials.