High temperature structural studies of Ba_2BiTaO_6

摘要

Synchrotron X-ray powder diffraction studies have shown that the Bi and Ta are ordered on the B-sites of the double perovskite Ba_2 BiTaO_6. At room temperature the structure is rhombohedral R3 and this transforms to a cubic structure Fm3m near 250 deg C. The R3 to Fm3m 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.