Unveiling local distortions in a putative rock salt high entropy oxide by RIXS

High entropy oxides with rock salt structure have been recently discovered and hold significant potential for applications in energy storage and catalysis. The high configurational entropy arising from the mixed occupation of the cation site is thought to compensate the unfavourable enthalpy of solution of CuO, due to the suppression, in the cubic structure, of the intrinsic Jahn-Teller effect of d9 Cu(II) ions. XRD and EXAFS measurements of Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O seem to evidence a departure from the cubic structure at 300 °C, and possibly already at room temperature, but are not conclusive. We, therefore, propose to determine the local symmetry at the Co, Ni and Cu sites by means of RIXS in order to better clarify the role of configurational entropy in Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O and possibly other high entropy oxides.