Correlations between thermoelectric properties and effective mass caused by lattice distortion in Al-doped ZnO ceramics

Doped ZnO has practical applications in the industry for thermoelectric generation, owing to its stability at high temperatures. However, the efficiency of energy conversion is not sufficient. In this work, we have focused on an experimental evidence of a first-principles prediction in ab-plane tensile strain and the effective mass behavior in ZnO ceramics. The results showed a systematic c-axis compression of the lattice up to c/a = 1.6010 with increase in the Al additive concentration. It was found that this lattice compression induced an increase in effective mass (m*) from 0.27 to 0.30 m0, leading to the enhancement in the Seebeck coefficient normalized by carrier concentration. Besides, both carrier concentration and Hall mobility increased with increase in Al additive concentration. It was concluded that in the ion-doped ZnO system, a high compression of c/a ratio due to heavy doping could be a key to improving the power factor.