The electronic structure of rare-earth oxides in the creation of the core hole

We studied the electronic structures of rare-earth sesqui-oxides R2O3 (R: rare-earth element) with a core hole, both experimentally and theoretically. The experimental study was made by measuring the rare-earth 3d X-ray photoemission spectra (XPS) of these oxides. Clear double-peak structures were observed for La2O3, the shoulder or broad foot of the low-binding-energy side of 3d XPS were observed for Pr2O3, Nd2O3, and Sm2O3, and single-peak structures were observed for Eu2O3, Gd2O3, and Dy2O3 The calculation of electronic structures was performed for the ground state and the 3d(-1) core-hole states by the spin-unrestricted DV-X alpha molecular-orbital method for model clusters chosen as [RO6](9-) for R2O3. The calculated results show the difference of the electronic structure in the ground state and the core-hole states. In the creation of the core hole, the number of unpaired 4f electrons increases by less than one due to the weak charge-transfer effect for La2O3 and Ce2O3, and this corresponds to the clear double-peak structure of the rare-earth 3d XPS. For Eu2O3 and Yb2O3, the number increases and decreases by less than 1 due to the restricted charge-transfer effect by filling 4f up arrow and 4f orbitals with electrons. Due to the strong charge-transfer effect, the number of unpaired 4f electrons increase by more than 1 for Pr-Sm oxides, and this effect produces, the shoulder or broad foot in the low-binding-energy side of the rare-earth 3d XPS peak. The decrease by more than 1 for Gd-Tm oxides results in clear single peak structures. The present results indicate that rare-earth sesqui-oxides can be classified into the four groups by spin response. (C) 2000 Elsevier Science B.V. All rights reserved.