Thermoelectric Properties of ZnO Ceramics Co-Doped with Al and Transition Metals

The effect of co-doping with transition metals (Fe, Ni, and Sm) on the thermoelectric properties of Al-doped ZnO (AZO) ceramics was studied. The electrical conductivity sigma of AZO was significantly (12%) increased by Ni co-doping, while an unfavorable deterioration in sigma was observed for Fe- or Sm-co-doped AZO. Hall-effect measurements indicated that the electron mobility of AZO decreased due to co-doping in all samples. Only the Ni-co-doped AZO sample showed significant enhancement in electron density, resulting in its black color. The thermal conductivity kappa decreased drastically due to Ni or Sm co-doping of AZO, while only a small change was observed for Fe co-doping of AZO. The kappa value at 1073 K for Ni-co-doped AZO was 77% of that for AZO. A dimensionless figure of merit ZT = 0.126 was attained at 1073 K for Ni-co-doped AZO, representing an improvement over that of conventional AZO by a factor of 1.50.