The effect of disorder in Ba2YTaO6 on the tetragonal to cubic phase transition

Synchrotron X-ray diffraction and Raman spectroscopy have been used to study the structure of the complex perovskite Ba₂YTaO₆, at temperatures down to 100 K. Where the Ta and Y cations exhibit long-range rock-salt like ordering, Ba₂YTaO₆ displays a continuous phase transition from a high temperature cubic structure, described in space group Fm3?m, to a tetragonal, I4/m, structure near 260 K. This transition is inhibited if extensive disorder and/or vacancies are/is present in the sample.