X-ray and neutron diffraction studies of coupled structural phase transitions in DyBaCo$_{2}$O$_{5.5}$

TL;DR

This study uses X-ray and neutron diffraction to investigate coupled structural phase transitions in DyBaCo$_{2}$O$_{5.5}$, revealing new low-temperature phases and their relation to magnetic anomalies.

Contribution

It reports the discovery of a new low-temperature phase transition in DyBaCo$_{2}$O$_{5.5}$ and clarifies the nature of the structural changes involved.

Findings

Identified a phase transition at ~322 K from Pmmm to Pmma.

Observed a first-order transition with hysteresis between 100-200 K.

Disproved the previously assumed Pcca space group for the low-temperature phase.

Abstract

A structural transition at $T\approx 322$ 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 TbBaCo$_{2}$O$_{5.5}$, 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 $T\approx 100$ and $T\approx 200$ K, which probably explains anomalous magnetic properties in this temperature range.