Thermal evolution of the EuBaCo2O5.5 crystal structure

Crystal structure of the EuBaCo2O5.502(1) perovskite obtained by equilibration and slow cooling in closed ampoule is studied between 100 400 ​K high-resolution synchrotron powder X-ray diffraction, its thermally induced phase transitions differential scanning calorimetry (DSC). The low-temperature Pmma supercell 2ap 2bp 2cp has Eu Ba alternating along c, Co3+ coordination square pyramids octahedra b orbital-order a. last order lost upon warming through a transition topping at 365 (ΔS ​≈ ​2.25R per mole EuBaCo2O5.5 DSC) that forms an ap as refined 380 ​K. DSC detects also twin magnetic 248 269 weak endothermic effects heating ​0.41 ​J/molK 0.19 ​J/molK, resp.). Intermittent negative thermal expansion some cobalt polyhedra discussed context possible spin states entropy change transition.