An experimental investigation of the electrical and thermal conductivity of iron and some dilute iron alloys at temperatures above 100°K

Abstract

Conductivity measurements have been performed at 90–300°K on iron of high purity and dilute alloys of this metal with Mn, Ni or Si. For the elimination of the parasitic thermal losses in the heat-conductivity measurements a special method has been worked out. The validity of the Wiedemann-Franz-Lorenz law (W-F-L law) for the investigated substances is examined. This analysis is extended to about 1300°K by use of conductivity values for iron and steels given in the literature. It is found that the part of the heat-resistivity of the electrons caused by lattice vibrations is fairly independent of temperature, in accordance with a previous statement by linde for non-transition metals. A modified form of the W-F-L law, written K e (ρ + \\ ̄ gr o) = LT, is put forward, and it is shown that this is generally valid for transition as well as non-transition metals at temperatures above the T 5-region of ρ. The constant \\ ̄ gr o of the suggested formula can be obtained from electrical measurements. If expressed as K g = K- K e , the lattice conductivity of iron shows an anomalous change at the Curie point, being much larger in the state of spontaneous magnetization than in the paramagnetic state. The spin-disorder part of the electrical resistivity is found to be proportional to T 3 in the temperature range < 1000°K. Some abnormal behaviour of the residual resistivity of iron when measured on wires of varying diameters is discussed. The general results of the investigation concerning ρ, K e and K g are given in the form of graphs of conductivity and resistivity-quantities as functions of temperature.