Abstract
Cation size effects were examined in the mixed A‐site perovskites La0.5Sm0.5CrO3 and La0.5Tb0.5CrO3 prepared through both hydrothermal and solid‐state methods. Atomically resolved electron energy loss spectroscopy (EELS) in the transmission electron microscope shows that while the La and Sm cations are randomly distributed, increased cation‐radius variance in La0.5Tb0.5CrO3 results in regions of localised La and Tb layers, an atomic arrangement exclusive to the hydrothermally prepared material. Solid‐state preparation gives lower homogeneity resulting in separate nanoscale regions rich in La3+ and Tb3+. The A‐site layering in hydrothermal La0.5Tb0.5CrO3 is randomised upon annealing at high temperature, resulting in magnetic behaviour that is dependent on synthesis route.
Highlights
Perovskites ABX3 are one of the most versatile group of materials in solid-state chemistry with respect to valence and ionic radii of the possible incorporated cations A and B, as well choice of anion X, from oxide to halides
A review of the literature shows that it is rare for stoichiometric perovskites to exhibit long-range A site order in the absence of an ordered B/B’ sublattice, with layering effects being observed only on the local scale without B site ordering in materials such as NaLa(BB’)O6 (B = Fe or Mn, and B’ = Nb or Ta), in which B site second-order Jahn–Teller effects and charge difference between the Na+ and La3+ are the driving mechanisms.[7]
In this paper we investigate the possibility of A site order in chromite perovskites, in which by using a single B site cation and isovalent lanthanides on the A site we negate the common mechanisms for A site order
Summary
Perovskites ABX3 are one of the most versatile group of materials in solid-state chemistry with respect to valence and ionic radii of the possible incorporated cations A and B, as well choice of anion X, from oxide to halides. Attempts were made to produce solid solutions with greater variance, such as La0.5Ho0.5CrO3 and La0.5Yb0.5CrO3 (the Supporting information, Figure S5); these did not result in single phases, suggesting the existence of a synthetic A-site radius variance limit.
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