Debye-Waller Factor Low Temperature Anomalies in BaPb1-xBixO3

Temperature dependent x-ray absorption investigations have been made on the Bi L3 edge in BaPb1-xBixO3 with x=0.0, 0.75, 1.0. Essentially abnormal behaviour of the Debye-Waller factor σ2 of Bi-O bonds was observed at low temperatures for BaBiO3 and BaPb0.25Bi0.75O3 in contrast to Einstein model. It was found that the Debye-Waller factors of both Bi-O bonds increase with temperature decreasing from ~90 K along with abnormal increasing of Bi-O and Bi-Ba distances. At the same time Pb-O, Pb- Ba bonds of BaPbO3 show normal behaviour with temperature. The nature of the anomalies is discussed in the frame of the dynamic fluctuation of the oxygen octahedra rotation mode that may give a new look to understanding of HTSC phenomenon in BaPb1-xBixO3 and Ba1-xKxBiO3