High temperature thermopower of sol–gel processed Zn_1−x−yAl_xMe_yO (Me: Ga, In)

In this study, dually doped samples of Zn_1−x−yAl_xMe_yO (Me: Ga, In) were prepared by sol–gel process followed by hot isostatic pressing for high temperature thermoelectric applications. Material characterizations were performed with differential thermal analysis-thermogravimetry, Fourier transform infrared spectroscopy and X-ray diffraction on the target phases. Successful doping of the samples was confirmed by X-ray photoelectron spectroscopy and energy dispersive X-ray analysis. Thermopower values of the samples are found to be relatively high in analogy to semiconducting behavior in which negative values indicate electrons are the dominant charge carriers (n-type). Substitution of Zn²⁺ by Ga³⁺ and In³⁺ for Zn_1−x−yAl_xMe_yO (Me: Ga, In) increases electron concentration in the samples and thereby decreases the thermopower values compared to Zn_0.98Al_0.02O. Considering the absolute values, In doped samples have higher thermopower (α_max = −162 µV/K at 585 °C for Zn_0.96Al_0.02In_0.02O) compared to the Ga doped sample. Al and In dually doped Zn_0.96Al_0.02In_0.02O could be considered as a promising n-type thermoelectric material for high temperature applications.