Transport properties of indium-alloyed and indium telluride nanostructured bismuth telluride

Nanostructured thermoelectric materials ideally reduce lattice thermal conductivity without harming the electrical properties. Thus, to truly improve the thermoelectric performance, the quality factor, which is proportional to the weighted mobility divided by the lattice thermal conductivity of the material, must be improved. Precipitates of In₂Te₃ form in the state-of-the-art Bi₂Te₃ with crystallographic alignment to the Bi₂Te₃ structure. Like epitaxy in films, this can be called endotaxy in solids. This natural epitaxy in a 3-dimensional solid is ideally situated to scatter phonons but produces minimal electronic scattering and, therefore, maintains high mobility. Here, we study the effects of In-alloying in Bi₂Te₃ at high In concentrations (about 4 at%), enough to produce the endotaxial microstructure. It is found that such concentrations of indium in Bi₂Te₃ significantly alter the electronic structure, reducing the effective mass and weighted mobility so significantly as to effectively destroy the thermoelectric properties even though the lattice thermal conductivity is successfully reduced.