We employed operando soft X-ray absorption spectroscopy (XAS) to monitor the changes in the valence states and spin properties of LaMn_1-x Co _x O₃ catalysts subjected to a mixture of CO and O₂ at ambient pressure. Guided by simulations based on charge transfer multiplet theory, we quantitatively analyze the Mn and Co 2p XAS as well as the oxygen K-edge XAS spectra during the reaction process. The Mn sites are particularly sensitive to the catalytic reaction, displaying dynamics in their oxidation state. When Co doping is introduced (x ≤ 0.5), Mn oxidizes from Mn²⁺ to Mn³⁺ and Mn⁴⁺, while Co largely maintains a valence state of Co²⁺. In the case of LaCoO₃, we identify high-spin and low-spin Co³⁺ species combined with Co²⁺. Our investigation underscores the importance to consider the spin and valence states of catalyst materials under operando conditions.

Iron(Fe)-water reactions in a magma ocean can influence water storage and density of planets. These reactions can form Fe-O-H phases, whose density, melting, and electronic properties at planetary interior conditions are important for informing planetary models. Here, we study natural goethite (α-FeOOH) that is shock-compressed along its principal Hugoniot. Analysis of our velocity interferometer system for any reflector (VISAR) results extends the equation of state to over 800 GPa. X-ray diffraction and VISAR reflectivity results indicate the onset of melting occurs at ~95 GPa with complete melting by 166 GPa, which may be relevant to low seismic velocity anomalies observed above the core-mantle boundary. Analysis of X-ray emission spectroscopy results up to 285 GPa shows the spin crossover of Fe, with dominantly low spin Fe above ~265 GPa in the melt, supporting formation of dense basal magma oceans in terrestrial planets. Using our measured FeOOH densities, we model planetary interiors up to 10 Earth masses. Assuming FeOOH forms via iron-water reactions, the radius decreases by up to 28%, while the density increases by up to 165% compared to the unreacted case, providing an avenue to investigate water storage and evolution in super-Earths and sub-Neptunes.

Co and Mn K-edge multiplets of bimetallic perovskite La₂CoMnO₆ nanoparticles (NP) and thin films are studied using high-resolution 1s2p resonant inelastic X-ray scattering (1s2p RIXS). Both the La₂CoMnO₆ NP and thin films exhibit Co²⁺ and Mn⁴⁺ valence states. A strong nonlocal peak is observed in the La₂CoMnO₆ NP, which becomes weaker in epitaxial La₂CoMnO₆ thin films grown on a SrTiO₃ (0 0 1) substrate. Guided by charge-transfer multiplet calculations, the Co and Mn 1s to 3d quadrupole pre-edge X-ray absorption near-edge structure (XANES) and 1s2p RIXS spectra were calculated, showing good agreement with experimental observations. Using Density Functional Theory (DFT) + U simulations, the metal ions 1s to nonlocal 3d-4p dipole transitions are successfully reproduced. The nonlocal peak can be explained as dipole transitions to metal–metal charge-transfer interactions facilitated by the oxygen 2p state. This study underscores nonlocal hybridizations beyond the local 1s to 3d quadrupole transitions in K-edge X-ray absorption spectra.