Noncubic layered structure of Ba 1 − x K x BiO 3 superconductor

Bismuthate superconductor ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{K}}_{x}{\mathrm{BiO}}_{3}$ $(x=0.27\ensuremath{-}0.49,{T}_{c}=25\ensuremath{-}32\mathrm{K})$ grown by an electrolysis technique was studied by electron diffraction and high-resolution electron microscopy. The crystalline structure thereof has been found to be noncubic, noncentrosymmetric and of the layered nature, with the lattice parameters $a\ensuremath{\approx}{\mathrm{a}}_{p},$ $c\ensuremath{\approx}2{\mathrm{a}}_{p}$ $({\mathrm{a}}_{p}$ is a simple cubic perovskite cell parameter) containing an ordered arrangement of barium and potassium. The evidence for the layered nature of the bismuthate superconductor removes the principal crystallographic contradiction between bismuthate and cuprate high-${T}_{c}$ superconductors.