SOFT-X-RAY-ABSORPTION STUDIES OF THE LOCATION OF EXTRA CHARGES INDUCED BY SUBSTITUTION IN CONTROLLED-VALENCE MATERIALS

We present high-resolution 2p x-ray-absorption spectra from 3d transition metals M in three series of pseudobinary and pseudoternary oxides. We show how the detailed shape of the multiplet within the spectra can be used to determine the valence of the M ions. The spectra of the early-transition-metal compounds show dramatic changes as a function of substitution due to changes in the M 3d occupancy, indicating that the extra holes or electrons are located predominantly at the 3d-metal sites. This contrasts strongly with the behavior of the spectra of late-transition-metal compounds, for which the extra charges induced by substitution go to oxygen states.