Structural characterisation of REBaCo2O6-δ phases (RE = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho)

REBaCo2O6-delta (RE = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho) phases were prepared by solid-state reaction at 1100 degrees C. Post-reaction heat treatments were carried out to alter the oxygen contents, which were determined by H-2-reduction thermogravimetry. Three closely-related structure types were observed, with the general sequence: tetragonal (delta >= 0.6) to orthorhombic (0.6 >= delta >= 0.4). to tetragonal (0.4 >= delta) with increasing oxygen content. Rietveld refinement of combined X-ray and neutron powder diffraction data of NdBaCo2O6-delta was carried out for four values of S. Oxygen deficiency is accommodated by partial occupancy of two sets of oxygen sites, giving a range of coordination environments for Co. Electron diffraction patterns revealed a superlattice similar to 2a(0) x 4a(0) x c(0) with Cmmm symmetry, where a(0) and c(0) refer to the (pseudo) tetragonal subcell. Tweed-like ferroelastic domains were routinely observed, suggesting that compositions that appear macroscopically tetragonal by X-ray diffraction are in fact orthorhombic with a approximate to b. (c) 2005 Elsevier SAS. All rights reserved.