Synthesis and characterization of telluride aerogels: Effect of gelation on thermoelectric performance of Bi ₂Te ₃ and Bi _2-xSb _xTe ₃ nanostructures

The synthesis and characterization of Bi ₂Te ₃ and Bi _2-xSb _xTe ₃ aerogel materials, and the effect of gelation on thermoelectrically relevant properties, is reported. Aerogels are prepared from oxidation of discrete thiolate-capped nanoparticles to yield a wet gel, followed by supercritical CO ₂ drying. The resultant aerogels have surface areas between 36 and 45 m ²/g. Characterization of the thermoelectric properties of hot-pressed pellets of Bi ₂Te ₃ aerogels suggested a decrease in lattice thermal conductivity with respect to the bulk materials, attributed to the effect of nanostructuring, but the power factor (S ₂σ) was also reduced due to the effect of adventitious doping. In the case of Bi _2-xSb _xTe ₃ aerogels, there was no change in the lattice thermal conductivity upon nanostructuring, but again the power factor was reduced with respect to bulk materials. This is attributed to the presence of excess tellurium, which led to compensation of the majority charge carriers. Proper carrier concentration optimization of the chalcogenide aerogel materials is needed if these materials are to be exploited in thermoelectrics.