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 R (3) over bar with further heating resulting in the loss of the tilting of the octahedra, the structure being in Fm (3) over barm. Cooling the sample induces an additional phase transition to a triclinic structure in I (1) over bar. Details of the various structures are presented. (C) 2009 Elsevier Inc. All Fights reserved.