Charge ordering in a 2D manganite, Pr0.25Ca1.75MnO4

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 and neutron powder diffraction. At room temperature, the K2NiF4-type structure is characterized by its ability to microtwine and form perovskite-like "pancake" defects, coherent with the matrix. The most important point concerns the appearance at low temperature of an incommensurate structure with a modulation vector (q) over right arrow approximate to 0.28 (c) over right arrow*, never observed to date in these 2D manganites. The reconstruction of the reciprocal space, using electron diffraction technique, evidences Cmca(00 gamma )s00 as the superspace group. The transition temperature, T-CO = 275 K, explains the anomalies of the rho (T) and M(T) curves, characterized by an increase of resistivity and appearance of antiferromagnetic fluctuations below this temperature.