Hall Coefficient of Metal–Ammonia Solutions

The Hall coefficient and electrical conductivity of Li–NH3, K–NH3, and Ca–NH3 solutions were measured as a function of concentration and temperature. The temperature range extended from 203–243°K and the concentration extended from metal saturation down to ≈ 4 MPM. The Hall coefficient was temperature independent for all solutions studied, but upon dilution, increased to values above the free-electron value at different electron concentrations for the monovalent and divalent solutions. The conductivity values ranged from 100–5000 Ω−1·cm−1, and dσ / dT was positive. Using an ionized impurity scattering model and an adjustable effective mass for the metal–ammonia solutions, a qualitative fit for the conductivity, Hall coefficient, and thermopower can be made in the region 4–8 MPM. The loss of degeneracy upon dilution seems to be responsible for anomalies in this region, and hence the metal–nonmetal transition can be narrowed down to the 1–4 MPM region.