The formation of precipitates in the ZnCoO system

Magnetic matter such as transition metals or metal oxides are able to exhibit ferromagnetism by the clustering in magnetic semiconductors. We fabricated Co-doped ZnO samples using the sol-gel method, and studied the magnetic precipitates in the samples by using both neutron diffraction and X-ray absorption fine-structure measurements. The structural details were characterized by X-ray and neutron diffraction, and the data were interpreted using Rietveld refinement. The doped Co ion was fully substituted into a ZnO lattice at 5 mol%, but the secondary phase of the Co3O4 was formed above 5 mol% of Co doping and its neutron diffraction signal increased up to 20 mol%. The quantitative amounts of each phase were calculated to be 55.43 wt.% of Co3O4 and 44.57 wt.% of fully cobalt-substituted ZnO. In the 30 mol% Co-doped sample, Co metal, as well as oxidized Co, were identified in this study. Those signals, however, were not observed by X-ray diffraction. To verify the local chemical bonding state, we used extended X-ray absorption fine-structure measurement and investigated the formation of precipitates by calculating the inter-atomic distance using Fourier analysis.