Gérard Lepoutre

PROPERTIES OF CONCENTRATED METAL-AMMONIA SOLUTIONS

Solutions of alkali metals in liquid ammonia exhibit metallic properties, which increase with concentration, with several fairly sharp ‘transitions’. We give a review of the most significant experimental properties and theoretical interpretations. We present a quantitative approach of a model in which all valence electrons are in a metallic band. Discussing the limits of this model, we give its qualitative physical interpretation, and are led to introduce complementary hypotheses, at increasing concentrations; excitation of solvated electrons to the ‘monomer’ or to a narrow band; formation of concentrated clusters in the dilute side and of clusters of solvated electrons in the concentrated side; deformation of the band by ‘potential wells’ due to solvation. Corrections must be made to the model of free electrons, even in the more concentrated range.

THERMOELECTRIC POWER AND THOMSON COEFFICIENT IN THE INTERMEDIATE RANGE OF CONCENTRATIONS

The thermoelectric power of the K-NH3 solutions in the concentration range x2 = 1 to 8.8 per cent has been measured as a function of temperature between — 65° and — 20°. The method used gives fast readings and might be applied to less stable solutions. The negative temperature coefficient and large anomaly of the thermoelectric power in the 1.5 to 2.7 per cent region have been related to formation of small aggregates of solvated cations over which are delocalized the electrons. The anomalies in compressibility, and temperature and pressure effects on electrical conductivity, at about two per cent, have been interpreted in the same way.