E L E C T R O N I C S T R U C T U R E , M A G N E T I S M A N D D Y N A M I C S
S C I E N T I F I C H I G H L I G H T S
1 0 0 H I G H L I G H T S 2 0 2 2 I
The larger deviation for BFYred indicates that deep structural reorganisation of the oxygen sublattice occurs, which cannot be modelled by the semi-empirical parameters. Several different oxygen arrangements around the cations have been explored, including an oxygen vacancy in the first coordination sphere (Figure 91b). This result indicates a preferential occupation of oxygen vacancies around the iron centres (instead of yttrium) and is in good agreement with DFT predictions in . The clustering of the vacancies leads to the presence of energetically inequivalent protonation sites that can explain the lower
proton uptake in Y-doped compared to Zn-doped samples.
This comprehensive study presents a consistent methodology (and its limitations) for simulating the O K-edge that is also expected to be largely applicable beyond barium ferrate perovskites. It demonstrates that it is possible to quantify the Fe O covalency based on the analysis of XRS spectra. The differences due to oxidation/ reduction and the introduction of oversized dopants can be correlated with the proton uptake, which helps to further optimise PCFC cathode materials.
PRINCIPAL PUBLICATION AND AUTHORS
Electronic modifications in (Ba,Sr,La)(Fe,Zn,Y)O3-δ unveiled by oxygen K-edge X-ray Raman Scattering, G. Raimondi (a), A. Longo (b,c), F. Giannici (d), R. Merkle (a), M.F. Hoedl (a), A. Chiara (d), C.J. Sahle (b), J. Maier (a), J. Mater. Chem. A 10, 8866-8876 (2022); https:/doi.org/10.1039/D1TA10211G (a) MPI-FKF, Stuttgart (Germany) (b) ESRF (c) CNR-ISMN, Palermo (Italy) (d) Università degli Studi di Palermo (Italy)
 R. Merkle et al., Annu. Rev. Mater. Res. 51, 461-493 (2021).  G. Raimondi et al., Chem. Mater. 32, 8502-8511 (2020).  J. Yoly, Phys. Rev. B: Condens. Matter Mater. Phys. 63, 125120 (2001).  A. Longo et al., ACS Catal. 10, 6613 (2020).
RIXS interferometry on a cluster Mott insulator
Novel magnetic phases of matter may emerge from unconventional magnetic moments with exotic exchange couplings. Resonant inelastic X-ray scattering (RIXS) measurements on the spin- liquid candidate Ba3InIr2O9 unravel the character of the magnetic moments. These arise from spin- orbit-entangled quasimolecular dimer orbitals. RIXS interferometry is the ideal tool to study such quasimolecular orbitals.
Mott insulators with localised spins provide a platform for quantum magnetism. Novel types of quantum magnets can be realised via unconventional exchange interactions. Such may be achieved in the presence of strong spin-orbit coupling. A topical example is the Kitaev quantum spin liquid, which features Majorana fermion excitations. It is based on bond-directional exchange, where different spin components are coupled along different bond directions. Such couplings are found in iridates with spin-orbit-entangled j=1/2 moments.
Fig. 91: a) Exemplary fits of O K-edge XRS for oxidised BLF and BFY. b) Best fit for reduced BFY, also including heavily distorted configurations, as illustrated at the bottom. Figures adapted from the principal publication.