Abstract
CoO-MgO samples (Co x Mg 1-x O : x = mol of Co / (mol of Co + mol of Mg)) were prepared by impregnation of MgO powder with an aqueous solution of CO(NO 3 ) 2 , followed by calcination at 773 K. The atomic concentration range of Co for formation of a solid solution and the state of Co ions dissolving in the samples were investigated mainly by XAFS. XRD patterns showed that the dominant phase is MgO in the samples of x 0.3. For the samples of > 0.5, the dominant phase was Co 3 O 4 and the MgO phase was not detected by XRD. Co K-edge XANES spectra demonstrated that the octahedral symmetry around Co ions in the sample of x = 0.02 is distorted in the samples of x ≥ 0.04, indicating the change in the state of dissolved Co ions. Co K-edge EXAFS spectra revealed that Co ions dissolve into MgO matrix substitutionally in the samples of x < 0.04 while the phase separation due to the formation of the Co 3 O 4 structure occurs in the samples of x ≥ 0.04.
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