White Lines and 3d-Occupancy for the 3d Transition-Metal Oxides

TL;DR

This paper uses electron energy-loss spectrometry to analyze white lines at L23 edges in 3d transition-metal oxides, establishing a correlation between white-line intensity and 3d occupancy, enabling valence state measurements.

Contribution

It introduces an empirical method to determine 3d-state occupancy changes from white-line intensity measurements in transition-metal oxides.

Findings

White-line ratio varies with 3d electron count.

Linear relationship between normalized white-line intensity and 3d occupancy.

Applied method to measure valence changes in Li_{1-x}Ni_{0.8}Co_{0.2}O_2.

Abstract

Electron energy-loss spectrometry was employed to measure the white lines at the L23 absorption edges of the 3d transition-metal oxides and lithium transition-metal oxides. The white-line ratio (L3/L2) was found to increase between d^0 and d^5 and decrease between d^5 and d^10, consistent with previous results for the transition metals and their oxides. The intensities of the white lines, normalized to the post-edge background, are linear for the 3d transition-metal oxides and lithium transition-metal oxides. An empirical correlation between normalized white-line intensity and 3d occupancy is established. It provides a method for measuring changes in the 3d-state occupancy. As an example, this empirical relationship is used to measure changes in the transition-metal valences of Li_{1-x}Ni_{0.8}Co_{0.2}O_2 in the range of 0 < x < 0.64. In these experiments the 3d occupancy of the nickel ion decreased upon lithium deintercalation, while the cobalt valence remained constant.