Accommodation of oxygen deficiency in La0.5Ca2.5Mn2O7-d and LaSr2Mn2O7-d Ruddlesden-Popper Manganites

Ruddlesden‐Popper (RP) (AO)(ABO 3 ) n mixed oxides have recently attracted considerable insight 1 as a consequence of their potential for low‐dimensional physic arising from their structural configuration which results from the ordered intergrowth between n ABO 3 perovskite (P) blocks and one AO rock‐salt (RS) layer. This ordered arrangement of different chemical and structural unities induces intriguing behaviours that can be modified by controlling the number of intergrowing unities. For instance, colossal magnetoresistance and ferromagnetic ordering have been reported by Moritomo 2 et al in n=2 La 2‐2x Sr 1+2x Mn 2 O 7 system. However, it should be noticed the difficulty to stabilize pure high ordered terms, which are frequently obtained as disordered intergrowths between the basic unities. We have prepared and characterized ordered n=2 terms for the La 0.5 Ca 2.5 Mn 2 O 7 and LaSr 2 Mn 2 O 7 compositions. For instance, figure 1 shows characteristic HAADF and ABF images atomically resolved for the strontium sample. In addition, compositional variations at the anionic sublattice are scarce compared to other manganese related perovskite systems in which different superlattices have been described as a consequence of the ordering on non‐occupied oxygen positions. In this work, we have also focused on the stabilization and characterization of new oxygen deficient La 0.5 Ca 2.5 Mn 2 O 7‐ d and LaSr 2 Mn 2 O 7‐ d phases. 3 The ensemble of XRD, ND, SAED, HREM and aberration corrected HAADF, ABF images as well as EELS techniques allows proposing a topotactic reduction process in both systems through different oxygen sites, apical and equatorial, for the strontium and calcium samples, respectively.