Europhys. Lett., 61 (4) , pp. 527-533 (2003)
bond length fluctuations in xJ. B. Goodenough, F. Rivadulla, E. Winkler and J.-S. Zhou
Texas Materials Institute, ME/MS & E, ETC 9.102, The University of Texas at Austin 1 University Station, C2201, Austin, TX 78712, USA
(Received 29 August 2002; accepted in final form 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 .
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.
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