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

Abstract

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.