Outstanding Atomic Order in Ruddlesden–Popper Oxide Microcrystals

Ruddlesden-Poppers manganates, A(n+1)Mn(n)O(3n+1), built from the ordered intergrowth between one rock-salt and n perovskite blocks, display a wide variety of functionalities related to their physical-chemistry properties which can be in principle tuned by chemical modifications. Nevertheless, the poor thermodynamic stability of the high members constitutes an inherent impediment, limiting the development of new functionalities in this family. Actually, for n >= 2, defects involving disordered intergrowths between perovskite and rock-salt blocks are always present avoiding the correct characterization of their properties. For that purpose, the use of sophisticated and expensive physical methods is required. In this article, the stabilization, following a chemical strategy, of micrometric La0.5Ca2.5Mn2O7 crystalline particles exhibiting a well ordered distribution of two perovskite and one rock-salt block, according to an ideal n = 2 unit cell, is reported. This apparently long-range structural ordering is linked to an unconventional short-range order-disorder phenomenon of La and Ca cations, characterized at the atomic level, which allows a rational explanation of the crystallochemical and magnetic properties of this Ruddlesden-Popper compound.