Modulation of thermoelectric properties of bulk ZnAlO by annealing in oxygen environment

Abstract

This manuscript reported the modulation of thermoelectric properties of ZnAlO by thermal annealing technique. The ZnAlO pellets were prepared by mixing of 99% Zinc (Zn) and 1% Al powders using hydraulic press and then annealed in an oxygen environment at various temperatures ranging from 500 to 900 °C. X-Ray Diffraction (XRD) data confirmed the hexagonal structure of Al doped ZnO and the crystal structure was found to be improved up to annealing temperature 700 °C and then degrade at annealing temperature 900 °C. The improvement in the crystal quality is related with the compensation of oxygen vacancy type defects by annealing up to 700 °C but further annealing causes oxygen atoms to occupy the interstitials sites therefore crystal degrades again. Fourier Transform Infrared Spectroscopy (FTIR) spectra consisted of ZnAlO peak along with other peaks due to hydroxyl groups as well. The Seebeck and Hall data suggested that the value of Seebeck coefficient, electrical conductivity and power factor were found to be increased up to annealing temperature 700 °C but decreased at further annealing. The increase in electrical conductivity is linked with the enhancement of Al solubility in the ZnO crystal by annealing. Al dopants in ZnO act as donor defects therefore resulted in the increase of electrical conductivity. But further annealing degrades the crystal quality and hence reduces the electrical properties.