Investigation of Local Structure of ZnO with High Doping Copper Concentration (≥13 %mole) Prepared by Co-Precipitation Method

Abstract

Cu-doped ZnO (CZO) with Cu %mole of 0, 13, 14, and 15% have been synthesized by the co-precipitation method with controlled pH at 9. The diffraction pattern of CZO shows that a single phase of ZnO with wurtzite structure (w-ZnO) was achieved in the parent compound. In contrast, small fractions of the secondary phase of CuO monoclinic (m-CuO) were identified in the doped compounds. Rietveld-refinement on the X-Ray Diffraction (XRD) patterns reveals that the crystallite size of CZO is estimated in the range of 84 - 148 nm with instrumental correction factor and that CZO14 exhibits the most considerable fraction of m-CuO among the samples. Interestingly, lattice constants decrease by Cu doping. The effects of Cu doping on the valence state and the local structure were investigated by X-Ray Absorption Spectroscopy (XAS). Based on our analysis on both Cu K-edge and Zn K-edge XANES spectra, oxidation states of Cu and Zn ions are about +2 with no evidence of other valence states. Cu atom is likely to incorporate into wurtzite crystal lattice by occupying Zn sites in a small portion, and the doped compounds create a few oxygen vacancies.