Realization of high thermoelectric power factor in Ta-doped ZnO by grain boundary engineering

Abstract

Electrical conductivity in nanostructured ZnO bulks is limited by the inherently low carrier mobility caused by the high density of grain boundaries and interfaces. In this study, Zn1−xTaxO (x = 0, 0.01, 0.02, 0.03) with micro/nanoplatelet structures composed of nearly coherent dense grain boundaries with a low misorientation angle of ∼4° between the grains was successfully fabricated. Despite the presence of a significant amount of grain boundaries and interfaces in the sintered bulk material, a high carrier mobility (52.2 cm2 V−1 s−1) was obtained in the composition Zn0.99Ta0.01O, which is comparable to the value shown by ZnO single crystals and far higher than their ordinary nanostructured counterparts (<15 cm2 V−1 s−1). In addition, the distortion of the density of states increased effective mass induced by Ta 5d hybridization in ZnO caused a Seebeck coefficient of −290 μV K−1 at 1002 K resulting in a high power factor of 15.2 × 10−4 W m−1 K−2 at 1002 K.