Thermoelectric properties of semimetal and semiconductor Bi$_{1-x}$Sb$_{x}$ foils and wires

The results of experimental investigations into the thermoelectric properties (electrical conductivity, thermoelectric power, and thermal conductivity) of microtextured foils and single-crystal wires based on semimetal and semiconductor Bi$_{1-x}$Sb$_{x}$ alloys are presented in the temperature range of 4.2–300 K. It is found that the band gap $\Delta E$ in Bi–17 at % Sb wires increases with decreasing wire diameter $d$, which is a manifestation of the quantum-size effect. At low temperatures ($T<$ 50 K), in the wires with $d<$ 400 nm, the electrical conductivity increases due to the significant contribution of highly conductive surface states characteristic of topological insulators. It is found for the first time that the thermal conductivity of semimetal Bi–3 at % Sb foils at low temperatures is two orders of magnitude lower, and that of semiconductor Bi–16 at % Sb foils one order of magnitude lower, than that in bulk samples of the corresponding composition due to significant phonon scattering at grain boundaries and surfaces. This effect leads to considerable enhancement of the thermoelectric figure-of-merit $ZT$ and can be used in miniature low-temperature thermoelectric energy converters.