The double-well oscillating potential of oxygen atoms in perovskite system Ba(K)BiO3: EXAFS – analysis results

Temperature-dependent X-ray absorption investigations were made on the Bi L3-edge in Ba1−xKxBiO3 with x=0.0, 0.4 and 0.5. For the superconducting samples (x=0.4 and 0.5) it has been found that the local structure differs from the ideal cubic in contrast to the neutron and X-ray diffraction data. The provided analysis of the EXAFS spectra indicates that the oxygen atoms move in double-well potential produced by the existence of two non-equivalent octahedral types of the oxygen environment of bismuth. The vibrations in such a potential lead to modulations of the Bi–O lengths with low frequency which is determined by the soft oxygen octahedron rotation mode frequency. This induces strong electron–phonon interaction and may be the reason for relatively high-temperature transition (Tc∼30 K) to the superconducting state.