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

A structural transition at T≈322 KT≈322 K from the PmmmPmmm to PmmaPmma 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 PccaPcca that has been chosen earlier as the highest subgroup of the PmmaPmma. The transition is of the first order with the temperature hysteresis, between T≈100T≈100 and T≈200 KT≈200 K, which probably explains anomalous magnetic properties in this temperature range.