Anomalous temperature behavior of BaBiO3

We have investigated the crystal structure of BaBiO3 at low temperatures using x-ray diffraction measurements. The polycrystalline sample was prepared by solid state reaction method. We have found that the structure of this compound changes to monoclinic primitive P2(1)/n phase from bodycentered I2/m phase at 140 K. The analysis of the refined parameters show that the tilting angle (phi) and Bi5+-O bond-lengths start changing at 250 K, much before the structural transition. On the onset of structural transition, the change in the tilting angle (f) and the Bi5+-O bond-lengths get saturated. Resistivity measurement shows change in activation energy to 0.54 eV from 0.27 eV below 205 K. This can be explained by the increase of tilting of the BiO6 octahedra, as it helps in localization of the electrons.