X-RAY ABSORPTION OF BABIO3 AND SUPERCONDUCTING BABI0.25PB0.75O3

X-ray-absorption studies of BaBiO3 and superconducting BaBi0.25Pb0.75O3 (Ba-Bi-Pb-O) did not show any structural transformations altering the gross-scale near-neighbor environment or the valence between 4 and 300 K. Two Bi-O distances, separated by about 0.17, could be distinguished for BaBiO3. Also in Ba-Bi-Pb-O, there is a strong indication of two different Bi-O distances, separated by about 0.12, but only one Pb-O distance. The differing Bi-O separations may be connected with local spatial charge fluctuations. The valence states of the two differently located Bi atoms could not be conclusively determined from the absorption-edge shape, but the Bi and Pb near-edge structures for Ba-Bi-Pb-O are nearly identical. The Bi-O and Pb-O vibrational frequencies, considered important for superconductivity, could be estimated from the temperature dependence of the broadening of the nearest-neighbor distributions; they correspond to Einstein temperatures of about 500 K. © 1990 The American Physical Society.