Role of Sintering Atmosphere and Synthesis Parameters on Electrical Conductivity of ZnO

ZnO-based compositions are of great interest for high-temperature thermoelectric applications. In this study, n-type Al-doped ZnO was sintered under varying atmospheres and the changes in electrical conductivity along with chemical defects were analyzed. The electrical conductivity of Al-doped ZnO (ZnO-Al) exhibited large variation from 10⁻⁵ to 10³ S/cm as the sintering atmosphere was changed from air to nitrogen to vacuum. The low oxygen partial pressure assisted Al substitution in ZnO and increased the interstitial Zn, which increased the carrier concentration and improved the electrical conductivity. Using vacuum sintering, the electrical conductivity of ZnO was enhanced as the concentration of Al doping was increased from 1 to 3 at.%. Two sets of starting powders were used for sintering studies, one synthesized through the ball-milling and other through the sol-gel chemical synthesis. It was found that the Al substitution is improved by using chemically synthesized ZnO-Al powders.