On the symmetry and crystal structures of Ba2LaIrO6

Accurate profile analysis of X-ray diffraction data was carried out to settle recent dispute on the symmetry and crystal structures of the double perovskite Ba2LaIrO6. Even through careful comparison of the full-width at half-maximum values, we found no evidence for Ba2LaIrO6 adopting either monoclinic (I2/m  ) or mixed rhombohedral (R3¯) and monoclinic (I2/m  ) structures at room temperature, becoming triclinic (I1¯) at below about 200 K. The correct space group is just R3¯ at temperatures between 82 and 653 K. Furthermore, the R3¯→Fm3¯m phase transition does occur in Ba2LaIrO6, but the transition temperature is found to be much higher than the reported value.

Observed (crosses) and calculated (continuous line) profiles of Ba2LaIrO6 at some selected temperature showing the region containing the basic (222), (321) and (400) reflections. Tick marks below indicate the positions of the allowed Bragg's reflections.Figure optionsDownload as PowerPoint slide