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

Abstract A structural transition at T ≈ 322 K from the P m m m to P m m a 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 DbBaCo2O5.5 by means of the X-ray and neutron diffraction. The low temperature phase does not belong to the space group P c c a that has been chosen earlier as the highest subgroup of the P m m a . The transition is of the first order with the temperature hysteresis, between T ≈ 100 and T ≈ 200 K , which probably explains anomalous magnetic properties in this temperature range.