X-ray and neutron diffraction studies of coupled structural phase transitions in DyBaCo2O5.5

A structural transition at T approximate to 322 K from the Pmmm to Pmma phase is found to coincide with an anomaly of resistivity. Another structural phase transition doubling the lattice parameter c, which has been postulated earlier to accompany a low-temperature magnetic transition in TbBaCo2O5.5, is observed in a single crystal DbBaCo(2)O(5.5) by means of the X-ray and neutron diffraction. The low temperature phase does not belong to the space group Pcca that has been chosen earlier as the highest subgroup of the Pmma. The transition is of the first order with the temperature hysteresis, between T approximate to 100 and T approximate to 200 K, which probably explains anomalous magnetic properties in this temperature range. (c) 2007 Elsevier B.V. All rights reserved.