The 1s x-ray absorption pre-edge structures in transition metal oxides

Abstract

We develop a general procedure to analyse the pre-edges in 1s x-ray absorption near edge structure (XANES) of transition metal oxides and coordination complexes. Transition metal coordination complexes can be described from a local model with one metal ion. The 1s 3d quadrupole transitions are calculated with the charge-transfer multiplet program. Tetrahedral coordination complexes have more intense pre-edge structures due to the local mixing of 3d and 4p states, implying a combination of 1s 3d quadrupole and 1s 4p dipole transitions. Divalent transition metal oxides can be described similar to coordination complexes, but for trivalent and tetravalent oxides, additional structures are visible in the pre-edge region due to non-local dipole transitions. The 1s 4p dipole transitions have large cross section at the 3d-band region due to the strong metal-metal interactions, which are oxygen mediated. This yields large intensity in the 3d-band region but at a different energy than the local 1s 3d quadrupole transitions because of smaller core-hole effects due to the delocalization of the excited electron.

Double perovskites as a family of highly active catalysts for oxygen evolution in alkaline solution

“…4a). The poor sensitivity of Co K-edge XAS for the oxidation state of cobalt greater than 3 þ can be attributed to higher hybridization of Co-O bonds 22 (Estimating hybridization of transition-metal and oxygen states in perovskites from O K-edge X-ray absorption spectroscopy, manuscript in preparation) in the Pr double perovskite than the Sm double perovskite, which is supported by O K-edge XAS measurements discussed below.…”

“…The hybridization of Co-O bonds was found to increase from Ho to Pr double perovskite based on the O K-edge XAS measurements. The pre-edge feature can be attributed to unoccupied O 2p states resulting from the mixing between O 2p and metal 3d states, and its intensity is linear with the number of holes in the O 2p-band 22 . The intensity of the pre-edge region (two peaks near B532-534 eV) increases with increasing ionic radius of the lanthanide ( Fig.…”

Spin-state studies with XES and RIXS: From static to ultrafast

“…These techniques probe the bulk properties of the sample, and are even compatible with extreme conditions due to the large penetration depths [12]. X-ray Absorption Spectroscopy (XAS) with its variants X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) have proven their utility in determining the unoccupied electron states and the local structure, respectively [13,14,15,16]. X-ray Emission Spectroscopy (XES) and Resonant Inelastic X-ray Scattering (RIXS) are very powerful in elucidating the electronic structure, providing information on the electron energies, local geometry, spin and valence state, etc.…”

Electronic fine structure calculation of metal complexes with three-open-shell s, d, and p configurations

“…Eventually, the presence of the inversion center in the T h point group allows us to neglect the impact of the 3d 5 → ns 1 3d 6 transitions, although they can also be calculated by means of the LFDFT. These transitions are strictly speaking not electricdipole allowed, but they are often visible in the observed Xray absorption spectra of transition metal compounds [40][41][42][43], more importantly when non-centro-symmetric objects are investigated. [44][45][46][47].…”

“…However, the 3d m → ns 1 3-d m+1 transitions are electric-quadrupole allowed, resulting in principle to very small intensities relative to the dipole ones [31,56]. However, we note that the 3d m → ns 1 3d m+1 transitions are often visible in the spectra of non-centro-symmetric compounds [40][41][42][43][44][45][46][47]. The possible mixing between the 3d orbitals with the 4p virtuals ensures a dipole character on the electron transition mechanism.…”