Thermal conductivity in complex metallic alloys: Beyond Wiedemann-Franz law

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In this work we consider the range of validity of the Wiedemann-Franz law (WFL) in quasicrystals, approximant phases, and giant unit-cell complex metallic alloys. In the limit of very low temperatures the WFL is satisfied, as expected, but as the temperature is progressively increased the Lorenz function deviates from the ideal behavior L(T)/L₀=1. Whereas the quasicrystalline sample exhibits a systematic and significant deviation for all considered temperatures, the other samples show the existence of a characteristic temperature signaling the onset of the anomalous behavior. This characteristic temperature is directly related to the unit-cell density of the sample and progressively takes on larger values as this density decreases. An alternative route to derive the lattice contribution to the thermal conductivity based on a simultaneous fitting analysis of the electrical conductivity sigma(T) and thermoelectric-power S(T) experimental transport curves is proposed. The capabilities of this approach are illustrated by studying the temperature dependence of the lattice contribution to the thermal conductivity in the (xi)'-AlPdMn giant unit-cell phase.
©2009 The American Physical Society. I am indebted to Jean Marie Dubois for his kind invitation to participate in the workshop Frontiers in Complex Metallic Alloys recently held in Zagreb, as a part of the activities of the Sixth Framework European Network of Excellence “Complex Metallic Alloys.” I warmly thank Ana Smontara for her kind hospitality when visiting the Institute of Physics in Zagreb and Ivo Batistić, Ante Bilušić, and Denis Stanić for interesting conversations. I am also indebted to Tsunehiro Takeuchi for insightful thoughts, to Janez Dolinšek for sharing with me his experimental data, and to Rogelio Rodríguez-Oliveros for his useful collaboration. I thank M. Victoria Hernández for a critical reading of the paper. This work has been supported by the Universidad Complutense de Madrid and Banco Santander under Project No. PR34/07- 15824.