A marked improvement in the thermoelectric performance of dense ZnO ceramics is achieved by employing a third element as a co-dopant with Al. Dual doping of ZnO with Al and Ga results in a drastic decrease in the thermal conductivity of the oxide, while the decrease in the electrical conductivity is relatively small. With the aid of a significant enhancement in the thermopower, the dually doped oxide shows thermoelectric figure of merit values, ZT, values of 0.47 at 1000 K and 0.65 at 1247 K at the composition Zn 0.96Al 0.02Ga 0.02O. These results appear to be the highest ZT values so far reported for bulk n-type oxides. Microscopic observation of the samples reveals a granular texture in the densely sintered oxide matrix, suggesting that considerable reduction of the thermal conductivity while maintaining high electrical conductivity could be achieved by such a bulk nanocomposite structure in the samples.
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