Dopant position of Co atom in Zn1-xCoxO nanoparticles studied by extended X-ray absorption fine structure

Zn1-xCoxO nanoparticles were prepared by sol-gel method. The microstructure and dopant position were studied by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and extended X-ray absorption fine structure (EXAFS). The XRD patterns did not show any signal of impurity in the Zn1-xCoxO nanoparticles with Co concentration from x = 0.01 to 0.08. Neither did the HRTEM image for the highest concentration sample with x = 0.08. The nanoparticles have also been investigated by the EXAFS measurements at Co k-edge. The radical distribution functions, the fitting result of bond length and coordination numbers, indicated there was an impurity in the highest Co concentration sample with x = 0.08. Although most of the Co atoms were substituted for Zn sites in ZnO with x = 0.08, a few of Co atoms formed a microstructure similar to Co3O4, which was not found in the XRD and HRTEM. The room temperature ferromagnetic behaviour was found for x = 0.01 sample by superconducting quantum interference device .