On the origin of the differences in the Cu K-edge XANES of isostructural and isoelectronic compounds

Abstract

Cu K-edge x-ray absorption near-edge structure (XANES) spectra of trigonal (3R) CuScO(2) and CuLaO(2) and of hexagonal (2H) CuScO(2) were investigated experimentally and theoretically, in order to study differences between spectra of isostructural and isoelectronic compounds. Significant differences were found in the Cu K-edge XANES of 3R CuScO(2) and 3R CuLaO(2); these differences can be understood by considering the calculated polarization dependence of the XANES spectra and the differences between the phaseshifts of Sc and La. Spectra of the 3R and 2H polytypes of CuScO(2) differ only weakly and the difference originates from the long-range order. The pre-edge peak around 8980 eV is generated by the same mechanism as the pre-edge peak in Cu(2)O, i.e. involving scattering by the Cu atoms in the plane which is perpendicular to the O-Cu-O axis.

XRD and XAS structural study of CuAlO2under high pressure

“…These compounds share the delafossite structure and are isoelectronic (Sc: 3d4s 2 , La: 5d6s 2 ). Following [27] they should show similar XANES spectra, which is not the case. XANES simulations including polarization were also performed [27], concluding that XANES differences originated from differences in the P c contribution, which are more influenced by the nature of the trivalent cation.…”

“…Following [27] they should show similar XANES spectra, which is not the case. XANES simulations including polarization were also performed [27], concluding that XANES differences originated from differences in the P c contribution, which are more influenced by the nature of the trivalent cation. The present single-crystal experiment, as well as previous CuGaO 2 data published in [13], add new elements to the above discussion.…”

“…This is not possible in other compounds such as Cu 2 O, where although there are also linear O-Cu-O bonds, their symmetric orientation gives rise to a global isotropic absorption. There are previous works [13,27] on the XANES spectra of CuGaO 2 , CuScO 2 and CuLaO 2 , but they were performed with powder samples. In figure 5 we present the XANES spectra in ambient conditions, for polarizations perpendicular (P ⊥ c) and parallel (P c) to the c axis, that is, to the Cu-O bond (see figure 1).…”

“…The energy shift between the calculated and experimental spectra, ∼4 eV, is of the order of magnitude in FEFF's self-consistent Fermi level estimates. XANES spectra have been previously measured [27] in powdered CuScO 2 and CuLaO 2 . These compounds share the delafossite structure and are isoelectronic (Sc: 3d4s 2 , La: 5d6s 2 ).…”

Zn K edge and O K edge x-ray absorption spectra of ZnO surfaces: implications for nanorods

“…Indeed, earlier experiments monitored a significant polarization dependence of Zn K edge and O K edge spectra of nanorods [2,4]. Polarized (angulardependent) spectra carry more information than unpolarized (orientationally averaged) spectra [19,20]. It would thus be interesting to learn whether the polarization dependence of XANES of ZnO nanorods bears some surface-specific markers or whether it is essentially bulk-like [1,21,22].…”