Thermoelectric properties of Bi and Bi2Te3 composites

It has been suggested that microengineering traditional thermoelectric materials into composites may lead to a significant improvement in their thermoelectric performance because of the reduction of phonon thermal conductivity from phonon scattering at the grain boundaries and interfaces. At the fundamental level the composite figure of merit ZT may be dramatically increased over that for bulk because of the increase of the electronic density of states that occur in low dimensionality systems. One approach for the fabrication of nanostructured materials is the utilization of nanochannel insulators as a matrix for the synthesis of dense composites using high pressure injection (HPI) of the semiconductor melt. We discuss the synthesis and structural properties of oriented Bi₂Te₃ nanowire arrays in Anopore porous alumina as well as random networks of Bi₂ Te₃ nanocrystals. The trigonal Bi₂Te₃ crystallites that form the wire are oriented with the basal plane of the hexagonal plane, i.e., the plane of highest conductivity, along the wire length. Bi wire arrays are similarly oriented. This structural effect is directly a result of the processing using the HPI technique. Another implication of our results is that wire arrays have a higher figure of merit than random networks