LOCAL OXYGEN OCTAHEDRA ROTATIONS IN BA1-XKXBIO3

We report XAFS analyses results of Ba0.6K0.4BiO3 in the temperature ra nge from 10K to 300K extending out to fourth nearest neighbors. The re sults show that the local structure differs substantially from the ave rage structure determined by neutron diffraction measurements. The res ults in superconducting Ba0.6K0.4BiO3, are consistent with oxygen octa hedra rotations either around [111] or [110] type axes. The rotation a ngles are 4.5 degrees up to at least T = 220K if the rotation is assum ed to be about [111] type axes: This local rotation exists in spite of the fact that the crystal is on the average cubic at all temperatures . The existence oi these local rotations suggests that the charge carr ier pairing mechanism may be enhanced through the interaction with the bistable states oi the oxygen octahedra as proposed by Plakida[4] and Hardy and Flocken[5].