Electronic modifications in (Ba,La)(Fe,Zn,Y)O3−δ unveiled by oxygen K-edge X-ray Raman scattering

Oxides with mixed protonic-electronic conductivity are relevant as oxygen electrodes for protonic ceramic fuel cells and electrolyzers. We investigate the modification of the electronic structure of (Ba,La)(Fe,Zn,Y)O3−δ when iron is partially replaced by Zn2+ or Y3+ and when it changes between 3+ and 4+ formal oxidation states. With a combination of X-ray Raman scattering (O K-edge) and X-ray absorption near edge structure (Fe, Zn, and Y K-edges) and the corresponding simulations reproducing the spectroscopic data, we quantitatively analyze the degree of covalency of the Fe-O bonds in reduced (Fe mainly 3+) and oxidized (Fe mainly 4+) materials. The simulations employ two semi-empirical par…