High temperature structural studies of Ba2BiTaO6

Synchrotron X-ray powder diffraction studies have shown that the Bi and Ta are ordered on the B-sites of the double perovskite Ba2BiTaO6. At room temperature the structure is rhombohedral R3¯ and this transforms to a cubic structure Fm3¯m near 250 °C. The R3¯ to Fm3¯m transition appears to be continuous. Although the temperature dependence of both the rhombohedral angle and volume strain show anomalous behavior, both are indicative of a second order phase transition.