Local structure of ${\mathrm{BaBi}}_{\mathit{x}}$${\mathrm{Pb}}_{1\mathrm{-}\mathit{x}}$${\mathrm{O}}_3$ 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 ${\mathrm{BaBi}}_{\mathit{x}}$ ${\mathrm{Pb}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{O}}_3$, for x=1, 0.75, 0.5, and 0.25. For the semiconducting end member, ${\mathrm{BaBiO}}_3$, two Bi-O distances, separated by 0.18 Å, 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 (${\mathit{V}}^{1/3}$) 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 ${\mathit{T}}_{\mathit{c}}$, in these oxides.