Electronic structure of RuSr2EuCu2O8studied by x-ray absorption and photoemission spectroscopies

Abstract

Local electronic structures of ruthenocuprate RuSr 2 EuCu 2 O 8 (RuEu-1212) were investigated by using x-ray absorption near-edge structure (XANES) and valence-band photoemission (VB-PES) measurements at room temperature, 80 K, and 25 K. The XANES results indicate that when RuEu-1212 is below Curie temperature, T M , electrons are transferred not only from Cu 3d states, but also from Ru 4 d states, to O 2p orbitals. Additionally, the partial spectral weight distributions derived from VB-PES measurements provide evidence of a weak overlapping between Ru 4 d states and strongly Cu 3d−O 2p hybridized states below the Fermi level, which results in a weak coupling between the CuO 2 and RuO 2 layers. The analysis of extended x-ray absorption fine structure shows that the appearance of weak ferromagnetism and superconductivity is accompanied by a significant decrease of dynamic local lattice distortions of high-shell Cu-Sr and Ru-Sr bonding in RuEu-1212.

Intermediate honeycomb ordering to trigger oxygen redox chemistry in layered battery electrode

“…For the lower energy region that represents the redox reaction, the calculated oxygen K -edge spectrum agrees well with the spectra from 528 to 533 eV. Thus, the peaks around 529 eV and 532 eV can be ascribed to the unoccupied hybridized orbitals of O 2 p –Ru t 2g and O 2 p –Ru e g , respectively3132. At the voltage plateau of 2.5 V, desodiation diminishes the O 2 p –Na 3 p signal, whereas the peak intensity of O 2 p –Ru t 2g (around 529 eV) increases on charging, indicating hole generation on the O 2 p –Ru t 2g orbital.…”

Quantification of Anionic Redox Chemistry in a Prototype Na-Rich Layered Oxide

“…Specifically, the intensity of the pre-edge features is determined by the strength of TM–O hybridization, which is naturally enhanced in charged states because the high-value state of TM hybridizes more strongly with O. , Figure b displays the O K-edge XAS spectra of Na 3 RuO 4 electrodes cycled to different SOCs. For the spectrum of pristine Na 3 RuO 4 , the pre-edge features around 529.5 and 531.5 eV correspond to the unoccupied O 2p–Ru t 2g and O 2p–Ru e g states, respectively, while the broad peak at 534.5 eV is related to the O 2p–Ru 5sp hybridization state. ,− The evolution of the pre-edge region in O K-edge XAS spectra reflects the oxidation state change of Ru. With the charge of the Na 3 RuO 4 electrode, electrons are extracted from the system through the desodiation process, resulting in the enhancement of the pre-edge region and thus the oxidation state of Ru.…”