Oxygen order–disorder phase transition in PrBaCo 2O 5.48 at high temperature

Abstract

We have investigated the PrBaCo 2O 5.48 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 CoO 6 octahedra and CoO 5 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 P 4 / mmm space group. The transition is caused by displacement of apical oxygen ions and is an indication that ionic conductivity, which has been observed in 3D cobaltites, may also exist in layered cobaltites.