J. Phys. IV France 7 (1997) C2-1081-C2-1083
Local Oxygen Octahedra Rotations in Ba1-xKxBiO3Y. Yacoby1, S.M. Heald2 and E.A. Stern3
1 Racah Institute of Physics, Hebrew University of Jerusalem, Jerusalem 91904, Israel
2 Argonne National Laboratory, 9700 S Cass ave., Argonne IL 60439, U.S.A.
3 Department of Physics, FM-15, University of Washington, Seattle WA 98195, U.S.A.
We report XAFS analyses results of Ba0.6K0.4BiO3 in the temperature range from 10K to 300K extending out to fourth nearest neighbors. The results show that the local structure differs substantially from the average structure determined by neutron diffraction measurements. The results in superconducting Ba0.6K0.4BiO3, are consistent with oxygen octahedra rotations either around  or  type axes. The rotation angles are 4.5° up to at least T = 220K if the rotation is assumed to be about  type axes. This local rotation exists in spite of the fact that the crystal is on the average cubic at all temperatures. The existence of these local rotations suggests that the charge carrier pairing mechanism may be enhanced through the interaction with the bistable states of the oxygen octahedra as proposed by Plakida  and Hardy and Flocken .
© EDP Sciences 1997