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

Temperature-dependent X-ray absorption investigations were made on the Bi L -3-edge in Ba1-xKxBiO3 with x = 0.0 h, 0.4 and 0.5. For the superconducting samples (x = 0.4 and 0.5) it has been found that the local structure diffe rs from the ideal cubic in contrast to the neutron and X-ray diffraction da ta. The provided analysis of the EXAFS spectra indicates that the oxygen at oms move in double-well potential produced by the existence of two non-equi valent octahedral types of the oxygen environment of bismuth. The vibration s in such a potential lead to modulations of the Bi-O lengths with low freq uency which is determined by the soft oxygen octahedron rotation mode frequ ency. This induces strong electron-phonon interaction and may be the reason for relatively high-temperature transition (T-c similar to 30 K) to the su perconducting state. (C) 2000 Elsevier Science B.V. All rights reserved.