bond length fluctuations in x
Texas Materials Institute, ME/MS & E, ETC 9.102,
The University of Texas at Austin 1 University Station, C2201,
Austin, TX 78712, USA
Accepted: 4 December 2002
We report a significantly stronger suppression of the phonon contribution to the thermal conductivity in x than can be accounted for by disorder of the 16% atomic vacancies present in . Since the transition from localized to itinerant electronic behavior is first order and has been shown to be characterized by bond length fluctuations in several transition-metal oxides with the perovskite structure, we propose that cooperative bond length fluctuations play a role in similar to the bond length fluctuations in the perovskites. This model is able to account for the strong suppression of the thermal conductivity, the existence of a pseudogap confirmed by thermoelectric power, an anomalously large Debye-Waller factor, the temperature dependence of the magnetic susceptibility, and the inability to order atomic vacancies in .
PACS: 74.25.Fy – Transport properties (electric and thermal conductivity, thermoelectric effects, etc.) / 71.27.+a – Strongly correlated electron systems; heavy fermions / 72.15.-v – Electronic conduction in metals and alloys
© EDP Sciences, 2003