Complex structural ordering of the oxygen deficiency in La0.5Ca2.5Mn2O7−δ Ruddlesden–Popper phases

Ruddlesden–Popper oxides, (AO)(ABO3)n, occupy a prominent place in the landscape of materials research because of their intriguing potential applications. Compositional modifications to the cation sublattices, A or B, have been explored in order to achieve enhanced functionalities. However, changes to the anionic sublattice have been much less explored. In this work, new oxygen‐deficient manganese Ruddlesden–Popper‐related phases, La0.5Ca2.5Mn2O6.5 and La0.5Ca2.5Mn2O6.25, have been synthesized by controlled reduction of the fully oxidized n = 2 term La0.5Ca2.5Mn2O7. A complete structural and compositional characterization, by means of neutron diffraction, electron diffraction and atomically resolved scanning transmission electron microscopy and electron energy‐loss spectroscopy techniques, allows the proposition of a topotactic reduction pathway through preferential oxygen removal in the [MnO2] layers along [031] and [] directions. The gradual decrease of the Mn oxidation state, accommodated by short‐range ordering of anionic vacancies, reasonably explains the breaking of ferromagnetic interactions reinforcing the emergence of antiferromagnetic ones. Additional short‐range order–disorder phenomena of La and Ca cations have been detected in the reduced La0.5Ca2.5Mn2O7−δ, as previously reported in the parent compound. New oxygen‐deficient manganese Ruddlesden–Popper‐related phases, La0.5Ca2.5Mn2O6.5 and La0.5Ca2.5Mn2O6.25, have been synthesized by controlled reduction of the fully oxidized n = 2 term La0.5Ca2.5Mn2O7. A complete structural and compositional characterization allows the proposition of a topotactic reduction pathway through preferential oxygen removal in the [MnO2] layers along [031] directions.