Oxygen order-disorder phase transition in PrBaCo2O5.48 at high temperature

We have investigated the PrBaCo2O5.48 Compound by means of neutron powder diffraction at temperatures 300 K < T < 820 K. We observe a new structural phase transition at T-OD = 776 K, which we associate with an oxygen order-disorder transition: the well-known room temperature ordered crystal structure, in which slabs Of CoO6 octahedra and CoO5 pyramids interleave (Pmmm symmetry) gets lost at temperatures T > T-OD, resulting in a statistical distribution of octahedra and pyramids in the sample. The new phase can be described by the tetragonal P4/mmm space group. The transition is caused by displacement of apical oxygen ions and is all indication that ionic conductivity, which has been observed in 3D cobaltites. may also exist in layered cobaltites. (c) 2006 Elsevier B.V. All rights reserved.