Ionic Wiedemann–Franz law

Abstract

The Wiedemann–Franz law for electron transport in metals was historically a linch pin for the free-electron theory of metals; it states that, at moderately low temperatures, the ratio of thermal conductivity K to electrical conductivity σ is proportional to absolute temperature, with a proportionality constant called “the Lorenz number” of L=2.45×10−8 W Ω/K2. Here we describe work on yttrium-stabilized zirconia in which we have found that a similar relationship is valid above 1350 K, where nearly all the electrical conduction and thermal conduction arise from ionic currents.