Transport Properties of Dilute Binary Magnesium Alloys

Abstract

Unusual lattice parameter behavior in dilute binary magnesium alloys has been observed by Raynor and others, and has been attributed to a Brillouin zone overlap phenomenon suggested by Jones. The primary purpose of this paper is to show that if the overlap model is even only qualitatively correct, measurements of electron transport properties should be sensitive to electron overlap. Such measurements have been made on the resistivity, temperature variation of resistivity, Hall coefficient, and thermoelectric power. Monovalent and divalent additions to magnesium are found to cause the Hall coefficient and thermoelectric power to vary monotonically with composition, but trivalent and quadrivalent additions cause these measurements to go through extrema associated with the zone overlap. It is proposed that both the Hall coefficient and the thermoelectric power may be expressed as the sum of two contributions. One contribution is directly related and therefore is linear to electron concentration. The other contribution arises essentially from everything else, particularly the perturbations upon the ion core potential when a foreign atom is introduced into the lattice. This latter contribution may be obtained directly from measurements on the magnesium-cadmium system. A simple subtraction then provides the electronic contribution for the alloy under question. A band picture is invoked to qualitatively justify this approach. Finally, this paper also demonstrates that Matthiessen's rule and Linde's rule are not valid for dilute magnesium alloys.