Ionic Wiedemann-Franz law

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 moder ately low temperatures, the ratio of thermal conductivity K to electrical c onductivity sigma is proportional to absolute temperature, with a proportio nality constant called "the Lorenz number" of L = 2.45 x 10(-8) W Omega/K-2 . Here we describe work on yttrium-stabilized zirconia in which we have fou nd that a similar relationship is valid above 1350 K, where nearly all the electrical conduction and thermal conduction arise from ionic currents. (C) 2000 American Institute of Physics. [S0003-6951(00)04042-0].