Electronic structure of CaMnOx with 2.66≤x≤3.00 studied with photoemission and x-ray-absorption spectroscopy

We studied the electronic structure of ClaMnO(x) (2.66 less than or equal to x less than or equal to 3.00) using x-ray photoemission and O 1s x-ray-absorption spectroscopy. Analyzing the spectra of the two end members with the configuration-interaction cluster model, we have determined all the main parameters of the electronic structure. We have found that the ground states of CaMnO2.5 and CaMnO3 are highly covalent, with approximately the same number of ligand holes per oxygen atom: 0.22-0.23. The-main separations between the Mn 3d bands closest to the Fermi level are of the order of 3 eV and the band gaps are of the charge-transfer type (U>Delta). The main effects of the oxygenation are the disappearance of the occupied e(g up arrow) band and an approximately rigid shift of about 1 eV to lower energies of all the other Mn 3d bands. Finally, we discuss the most probable causes for the absence of a metallic phase in CaMnOx.