Heavy element doping for enhancing thermoelectric properties of nanostructured zinc oxide

ZnO is a high melting point, high charge carrier mobility semiconductor with potential as a thermoelectric material, but its high thermal conductivity kappa is the limiting factor for increasing the thermoelectric figure of merit ZT. Here, we demonstrate that doping ZnO with heavy elements can significantly enhance ZT. Indium doping leads to ultralow kappa similar to 3 W m(-1) K-1 and a high power factor alpha(2)sigma similar to 1.230 x 10(-3) W m(-1) K-2, yielding ZT(1000K) similar to 0.45 that is similar to 80% higher than non-nanostructured In-Zn-O alloys. Although Bi doping also yields a high Seebeck coefficient of alpha(300K) similar to 500 mu V K-1, Bi segregation, grain growth and defect complexing are unfavorable for increasing ZT. Thus, besides increased impurity scattering of phonons, the concurrence of nanostructuring and charge carrier concentration control is key to ZT enhancement. Our results open up a new means to realize high ZT thermoelectric nanomaterials based on ZnO.