Aurel-Mihai Vlaicu

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

Abstract We studied the electronic structures of rare-earth sesqui-oxides R 2 O 3 (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 La 2 O 3 , the shoulder or broad foot of the low-binding-energy side of 3d XPS were observed for Pr 2 O 3 , Nd 2 O 3 , and Sm 2 O 3 , and single-peak structures were observed for Eu 2 O 3 , Gd 2 O 3 , and Dy 2 O 3 . The calculation of electronic structures was performed for the ground state and the 3d –1 core-hole states by the spin-unrestricted DV-Xα molecular-orbital method for model clusters chosen as [RO 6 ] 9– for R 2 O 3 . 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 La 2 O 3 and Ce 2 O 3 , and this corresponds to the clear double-peak structure of the rare-earth 3d XPS. For Eu 2 O 3 and Yb 2 O 3 , the number increases and decreases by less than 1 due to the restricted charge-transfer effect by filling 4f↑ 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.

The contribution of the ligands around Cr to the resonant inelastic L X-ray emission spectra

Abstract L X-ray emission spectra in the energy region of the Cr 2p threshold on Cr compounds were measured and analysed using tunable synchrotron radiation. The X-ray absorption and emission spectra (XAES) of Cr (VI) are very different from those of Cr (III). It is considered that the difference in the soft X-ray emission is mainly attributed to the effect of the covalency in bonding, because the transition intensity of the Kβ 2 spectral line is sensitive for the valence electronic configuration. Therefore, it follows that XAES is very sensitive to the ligand environment in Cr compounds and relatively insensitive to the metal oxidation state, as Grush et al. suggested for Mn complexes [J. Electron. Spectros. Relat. Phenom. 92 (1998) 225].

K X-ray emission spectra of Ni in nickel(II) Schiff base complexes

K x-ray emission spectra of Ni were measured in bis(N-isopropylsalicylideneaminato)nickel(II) and bis(N-isobutylsalicylideneaminato)nickel(II) with different types of coordination, planar or pseudo-tetrahedral, using a double-crystal x-ray spectrometer. The relationship between the magnetic susceptibility and the energy spectra of the Kβ2,5 and Kβ′ emission lines was investigated for these compounds. The electronic structures of the compounds were also studied by the use of the molecular orbital method. Copyright