Metal-nonmetal transition in metal-ammonia solutions via the inhomogeneous transport regime

Abstract

In this paper we present a coherent physical picture of the metal-nonmetal transition in metal-ammonia solutions in the intermediate concentration range. We propose that in Li-NH3 and Na-NH3 solutions at T - T, 10-20 K the metallic propagation regime (9-16 MPM) is separated from a nonmetallic pseudointrinsic semiconducting regime (1-2.3 MPM) by a microscopically inhomogeneous regime (2.3-9 MPM) in which the concentration fluctuates locally about either of two well-defined values Mo and MI, Mo > MI, the local concentration remaining near Mo or M1 over radii approximately equal to the Debye short correlation length, b, for concentration fluctuations. The limits of the inhomogeneous regime were determined from a combination of concentration fluctuation measurements, electrical conductivity, Hall effect, and paramagnetic susceptibility data to be Mo = 9 MPM and MI = 2.33 MPM, which yield the C scale, C = (M - 2.33)/6.66, for both Li-NH3 at 223 K and for Na-NH3 at 240 K. We have also established the consistency of our picture with the available magnetic data for Na solutions. An analysis of electronic transport, thermal transport, optical properties, and sound velocity was carried out in terms of a theory of response functions for microscopically inhomogeneous materials developed by us. Excellent agreement between theory and experiment was obtained throughout the entire inhomogeneous transport regime.