X-ray absorption fine spectroscopy (XAFS) measurements were performed in the fluorescence mode using a Lytle detector at beamline 01C1 of National Synchrotron Radiation Research Center (NSRRC) in Taiwan. The electron storage ring was operated at 1.5 GeV with a constant current of ~ 360 mA. A Si (111) Double Crystal Monochromator (DCM) was used to scan the photon energy. XANES analysis were conducted using the Athena software based on the IFEFFIT program to determine the structural environment of Co atoms. Averaged XAS spectra were first normalized to the absorption edge height, and the background was removed using the automatic background subtraction routine AUTOBK implemented in the Athena software . A reference foil of Co foil was used for energy calibration of the monochromator, which was applied to all spectra. The Co K-edge calibration was set to the first inflection point of the reference foil, set at 7709 eV for easy comparison with other work . Quantitative information on the radial distribution of neighboring atoms surrounding Co atoms was derived from the extended absorption fine structure (EXAFS) data. An established data reduction method was used to extract the EXAFS χ-functions from the raw experimental data using the IFEFFIT software.