| Abstract
| - The structural study of the manganite Pr0.25Ca1.75MnO4, n = 1 member of the Ruddlesden−Popper (RP) family, has been carried out using high-resolution electron microscopy andneutron powder diffraction. At room temperature, the K2NiF4-type structure is characterizedby its ability to microtwine and form perovskite-like “pancake” defects, coherent with thematrix. The most important point concerns the appearance at low temperature of anincommensurate structure with a modulation vector q⃗ ≈ 0.28c⃗*, never observed to date inthese 2D manganites. The reconstruction of the reciprocal space, using electron diffractiontechnique, evidences Cmca(00γ)s00 as the superspace group. The transition temperature,TCO = 275 K, explains the anomalies of the ρ(T) and M(T) curves, characterized by an increaseof resistivity and appearance of antiferromagnetic fluctuations below this temperature.
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