Synthesis and structural characterization of ZnO doped with Co

Abstract

Co-doped Zn1−xCoxO nanoparticles were prepared by hydrothermal synthesis. The morphology, solid solubility and local atomic structure around the doping Co atoms were investigated. The morphologies of Co-doped ZnO nanoparticles were observed by scanning electron microscopy. The crystal structure of nanoparticles and the possible impurity phase were analyzed by X-ray diffraction patterns. The local atomic arrangements were studied by X-ray absorption fine structure spectroscopy. The substitution of Co for Zn was confirmed by diffraction anomalous fine structure spectra. The results demonstrated that Zn1−xCoxO can form a single phase of Co-doped ZnO with x⩽0.03. But it is a mixture of Co-doped ZnO and Co(OH)2 phases with x⩾0.05. Hydrothermal temperature can decrease the solid solubility of Co in ZnO lattice. Polar molecules can control the morphology of the nanoparticles. The Co-doped ZnO nanoparticles take a rod-like shape and the axial direction of the nanorods is along the c-axis direction of hexagonal wurtzite unit cell. A mixed-valence state of Co2+ and Co3+ is identified for the Co-doped ZnO nanoparticles. Diffraction anomalous fine structure technique could be used to determine the solid solubility of impurity when only one equivalent crystalline site in the host crystal is replaced by the impurity atoms. The Co-doped ZnO particles were identified to have room-temperature ferromagnetic properties.