Influence of the Preparation Conditions on the Thermoelectric Properties of Al‐Doped ZnO

Abstract

ZnO‐based materials are among the best n‐type thermoelectric oxides known to date, with a thermoelectric figure of merit that reaches ZT=0.65 at high temperature. However, there is a large dispersion of the data reported in the literature and a controversy recently appeared about the real potential of these materials for thermoelectric conversion. In this paper, we report on a careful study of the influence of the preparation conditions, particularly the annealing atmosphere, on the thermoelectric properties of Al‐doped ZnO. Our thermopower and electrical resistivity measurements evidenced a large difference between air‐prepared and N2‐prepared samples, the power factor S 2σ being more than twice larger for the latter. This difference is linked to the presence of oxygen vacancies after annealing under nitrogen as evidenced by thermogravimetric analysis. Cycling experiments showed that the carrier concentration can be reversibly changed by successive annealing under different atmosphere. These results raise questions concerning the stability of the best thermoelectric ZnO‐based materials, which are prepared under nitrogen, during long‐term use at high temperature in air in thermoelectric conversion devices.