LOCAL-STRUCTURE OF BABIXPB1-XO3 DETERMINED BY X-RAY-ABSORPTION SPECTROSCOPY

X-ray-absorption fine-structure (XAFS) spectroscopy was employed to study the near-neighbor environments of the Bi and Pb atoms in the perovskite-structured material BaBi(x)Pb1-xO3, for x = 1, 0.75, 0.5, and 0.25. For the semiconducting end member, BaBiO3, two Bi-O distances, separated by 0.18 angstrom, could be distinguished, consistent with diffraction results. After alloying with Pb, two Bi-O distances are still observed in the semiconducting alloys (x = 0.75 and 0.50) as well as in the metallic and superconducting phase (x = 0.25). In all the alloys, the two Bi-O distances and their separations decrease somewhat with increasing Pb concentration. The weighted average of the Bi-O and Pb-O distances is consistent with half the pseudocubic cell edge (V1/3) determined from diffraction. The different Bi-O bond lengths are accompanied by charge-density fluctuations which may enhance local, breathing-type phonon modes and thereby increase the coupling between electron and phonon states. For the metallic and superconducting phase, these fluctuations are consistent with a local charge-density-wave picture and the presence of a pseudogap. These results may have implications for the superconductivity, with a relatively high T(c), in these oxides.