The Wiedemann–Franz (WF) law is a fundamental, empirical law that originally relates the electronic thermal conductivity (Λe) of a metal to its electrical resistivity (ρ) via the Lorenz number L = ρΛe/T, where T is the absolute temperature. Conventionally as ρ is measured or calculated, it has often been used to infer the Λe through the WF law at a wide range of pressure (P)–temperature (T) conditions. However, since the WF law was originally formulated based on a simple electron gas model with L being approximately the Sommerfeld value L0 = 2.44 × 10−8 W Ω K−2, its validity to transition metals involving correlated d-orbital electrons at a variety of P-T conditions has been questioned, not to mention to metallic alloys. Here, we report experimental measurements on the thermal conductivity and electrical resistivity of platinum (Pt), iron (Fe), as well as Fe0.85Si0.15 and FeS alloys at high pressures and room temperature. We demonstrate that the L of Pt and Fe both reasonably agree with L0 from ambient to ∼60 GPa, except for Fe around the pressures where a structural transition (∼12 GPa) and an electronic topological transition (∼30–40 GPa) occur. The L of Fe0.85Si0.15 and FeS alloys, however, both considerably deviate from L0, presumably due to significant inelastic scatterings between carriers and impurities. Our results suggest that using the WF law with ideal L0 to convert ρ of metallic alloys to Λe (and vice versa) at high pressures could lead to a large discrepancy from that obtained by direct measurements.

中文翻译：

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在高压下测试金属和合金的 Wiedemann-Franz 定律的有效性


Wiedemann-Franz （WF） 定律是一个基本的实证定律，它最初通过洛伦兹数 L = ρΛe/T 将金属的电子热导率 （Λe） 与其电阻率 （ρ） 联系起来，其中 T 是绝对温度。通常，当 ρ 被测量或计算时，它通常用于在很宽的压力 （P）-温度 （T） 条件下通过 WF 定律推断 Λe。然而，由于 WF 定律最初是基于一个简单的电子气模型制定的，其中 L 大约是 Sommerfeld 值 L0 = 2.44 × 10-8 W Ω K-2，因此它对在各种 P-T 条件下涉及相关 d 轨道电子的过渡金属的有效性一直受到质疑，更不用说对金属合金了。在这里，我们报告了铂 （Pt）、铁 （Fe） 以及 Fe0.85Si0.15 和 FeS 合金在高压和室温下的热导率和电阻率的实验测量结果。我们证明，Pt 和 Fe 的 L 都与从环境温度到 ∼60 GPa 的 L0 合理一致，除了 Fe 在压力附近发生结构转变 （∼12 GPa） 和电子拓扑转变 （∼30–40 GPa）。然而，Fe0.85Si0.15 和 FeS 合金的 L 都与 L0 有很大偏差，这可能是由于载流子和杂质之间显着的非弹性散射。我们的结果表明，在高压下使用具有理想 L0 的 WF 定律将金属合金的 ρ 转换为 Λe（反之亦然）可能会导致与直接测量获得的结果存在很大差异。