L3/L2 white-line intensity ratios in the electron energy-loss spectra of 3d transition-metal oxides

The L3/L2 white-line intensity ratio in transition-metal oxides deviates widely from the statistical value of 2 : 1 but shows interesting systematics. In a series of oxides of a given metal, the ratio reaches a maximum for the d5 configuration (e.g. MnO) and a minimum for the d0 configuration (e.g. KMnO4). In a series of monoxides, sesquioxides and dioxides of different metals, the ratio is again a maximum at the d5 configuration and decreases as the configuration changes towards d0 or d10. Our results, obtained by electron energy-loss spectroscopy, carried out in an electron microscope, are interpreted on an atomic mechanism involving spin-spin coupling. According to this model, the L2 transition probability decreases in the progression d0 to d5 whereas the L3 transition probability decreases beyond d5.