Structural studies of the phases in Ba2LaIrO6—New light on an old problem

Accurate and precise structures for the cation-ordered double perovskite Ba2LaIrO6 at a number of temperatures are presented. Careful analysis of the synchrotron X-ray and neutron diffraction profiles of Ba2LaIrO6 suggests that, at room temperature, this is monoclinic in space group I2/m. Heating the sample to 375 K results in a transition to a rhombohedral phase in R3¯ with further heating resulting in the loss of the tilting of the octahedra, the structure being in Fm3¯m. Cooling the sample induces an additional phase transition to a triclinic structure in I1¯. Details of the various structures are presented.