The electronic structures of a wide range of transition-metal compounds, including Cu, Ni, Co, Fe, and Mn oxides and sulfides, with metal valences ranging from 2+ to 4+, have been investigated by a cluster-type configuration-interaction analysis of the core-level 2p x-ray photoemission spectra. We show that by including the d-d exchange interaction (retaining only diagonal terms) and an anisotropic metal-ligand hybridization in the model, these spectra can be well reproduced, and so can be used to deduce quantitatively values for the ligand-to-metal charge-transfer energy 5, the on-site d-d Coulomb repulsion energy U, and the metal-ligand transfer integrals T. Systematics for 6 and U are generally consistent with those found from previous valence-band studies and follow expected chemical trends. By using values of 5 and U found from this model, we show that most of the transition-metal compounds studied in this work can be classified in the charge-transfer regime of the Zaanen-Sawatzky-Allen diagram. A few exceptions to these systematics have been found. Small U values found for pyrite-type CoS& and FeS2 and large T values for Mn perovskite oxides, as well as the neglect of other mechanisms such as exciton satellites, may indicate a limitation of the local-cluster model.

The electronic structure of Lal Sr MnQ3 has been studied by photoemission and Q 1s x-rayabsorption spectroscopy. Spectra of the Mn 2p core levels and the valence bands for LaMnQ3 and SrMnQ3 have been analyzed using a configuration-interaction cluster model. The ground state of LaMnQ3 is found to be mixed d and d I states and that of SrMnQ3 to be heavily mixed d and d 1.states, rejecting their strong covalency. The character of the band gap of LaMnQ3 is of the p-to-d charge-transfer type while that of SrMnQ3 has considerable p-p character as well as p-d character. Holes doped into LaMnQ3 mainly of oxygen p character are coupled antiferromagnetically with the d local moments of the Mn + ions and become itinerant, thus aligning the Mn moments ferromagnetically. The changes in the electronic structure with carrier doping are not of the rigid band type: By La substitution for SrMnQ3, the so-called in-gap spectral weight (of e"~s ymmetry) appears with its peak located 1 -2 eV below the Fermi level and grows in intensity with increasing La concentration, while the spectral intensity of the eg~s tates above the Fermi level decreases, showing a transfer of spectral weight from the unoccupied to the occupied eg~s tates with electron doping. Meanwhile, the intensity at the Fermi level remains low even in the metallic phase (0.2~x~0.6). The energy shifts of core-level peaks and valence-band features with x suggest a downward shift of the Fermi level with hole doping, but the shift is found to be very small in the metallic phase. The importance of the orbital degeneracy of the e~~b and and possible orbital fiuctuations in the ferromagnetic phase are pointed out.

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