origin of FM correlations in Ca2Mn2-xRuxO7 (0.1

We observed unexpected features of Ca2Mn2-xRuxO7 at Ru L3 with HERFD-XAS, whose origin cannot be purely electronic. EXAFS (and XANES) at the Mn and Ru K edges would definitely unveil the local distortions that may appear on Mn/RuO6 with doping, which would be key to interpret the HERFD-XANES data (at Ru L3) and to separate electronic and local structural components. The recently obtained -K3MnO4 phase has never been studied as a cathode material. It can extract a potassium ion at the average potential of 2.7V vs K+/K to form at the end of the charge (3.8 V) the K2MnO4 phase. At higher potential (4.2V vs K+/K), it seems that it can form a phase close to KMnO4. Ex situ XRD measurements are carried out to confirm this hypothesis.The evolution of the Mn oxidation state and the change of the local structure allow us to understand the redox mechanism associated with the extraction of potassium and its impact on the reversibility of the cycling.