Vapor-deposited metal-gas alloys of sodium and ammonia

Films of sodium and ammonia were formed directly from vapor onto substrates held at or below 5 K. The electrical resistivity of the films was measured as a function of sodium concentration. A metal-nonmetal transition as a function of composition was observed at concentrations in the 45-50 mole % range. The transition was found to be anomalous in that the resistivity was not a monotonic function of the sodium concentration. The data indicate that there is enhanced conductivity over a narrow concentration range on the nonmetal side of the transition. The conductivity is not magnetic field dependent up to the maximum available field of 4 kOe. No evidence was found for the anomalous electrical conductivity previously reported for bulk, dilute sodium-ammonia solids that were quick-frozen from liquid solutions.