Resolution of the Conductivity Dilemma in Liquid Solutions of Alkali Metals in Alkali Halides

Abstract

Nuclear magnetic resonance measurements are reported for liquid Na-NaBr, Cs-CsCl, and Cs-Csl solutions containing less than 10 mole% metal. Correlation of the resonance shifts, relaxation rates, and dc electrical conductivity shows that the electronic mobility is independent of concentration in Na-NaBr, in sharp contrast with the cesium solutions. The results provide an explanation for the apparently anomalous electronic conductivity observed in liquid-sodium-sodium-halide solutions.

Nonmetal-metal transition in metal–molten-salt solutions

“…Na solutions show a characteristic anomalous behavior since some properties differ significantly from those of the heavier alkali metals. 2,5,11,[21][22][23][24] In particular, the electronic conductivity has a sublinear dependence on x over a range of temperatures, a feature which is not observed in the other solutions. 2 The outline of the paper is as follows.…”

“…As possible candidates, the formation of Na 2 molecules 21 and/or Na Ϫ ions has been suggested. 5 Furthermore, in Na-NaBr, the optical absorption spectrum, which is usually considered the strongest evidence in favor of the F-center model, has a number of peculiar features. 23 The peak energy does not satisfy the Mollwo-Ivey relation, as in the other solutions.…”

“…21 The sublinear dependence on x of the electrical conductivity could be related to the formation of long-lived nonmagnetic and nonconducting species. 5 The effect of such species is to remove excess electrons from the conduction process. As possible candidates, the formation of Na 2 molecules 21 and/or Na Ϫ ions has been suggested.…”

“…[2][3][4][5][6][7][8][9][10][11] Low concentrations of excess electrons are localized. 25 In principle different configurations are possible: neutral alkali atoms, multisite localized states, and F centers.…”

“…Among the systems where the NM-M transition has been observed, metal-molten-salt solutions of the type M x (M X) 1Ϫx have been studied extensively through experiments, [2][3][4][5][6][7][8][9][10][11] computer simulations, [12][13][14][15] and theory. 1,[16][17][18] The alkali metals dissolve in molten alkali halides to form true solutions.…”