Measurement of the Hall Effect in Metal—Ammonia Solutions

Abstract

The Hall effect in solutions of Li (1.5 to 20 mole % metal), Na (0.3 to 8 mole %), and Ca (4 to 9 mole %) in liquid ammonia has been measured. Solutions above about 4 mole % were found to have a free-electron (metallic) Hall coefficient given by RH = (ne)−1, where n is the metallic valence-electron concentration. The corresponding Hall mobility is related to the metal concentration x, expressed in mole percent metal, by the simple power law μ∝x2m, where m is about 2.2 in Li and Na Solutions, and 1.0 in Ca solutions. The mobility increases from 0.6 cm2/V·sec at 5 mole % to 20 cm2/V·sec at 20 mole %. Upon dilution below 4 mole %, the Hall coefficient and mobility rapidly increase several orders of magnitude. This effect is indicative of a metal—nonmetal transition. The mobility of a Na solution has a maximum of 200 cm2/V·sec at 0.5%. The experimental techniques are discussed briefly and the results are compared with other experiments.