The electronic and ionic structures of metal-ammonia solutions

Presently existing data on the properties of liquid metal-ammonia solutions are reviewed critically in relation to physical models and current theory. Emphasis is given to the inter-relation between the electronic properties and the atomic structures of the solutions. The material is organized according to concentration regions characterized by differing electronic and ionic structures. In the very dilute concentration range, 0–10⁻³ mole per cent metal (MPM), the solutions behave as ideal electrolytes with solvated electrons and solvated positive ions as the ionic species. Association of these species occurs in the dilute region, 10⁻³–10⁻¹ MPM. We propose that growth of associated complexes into large, metallic clusters occurs in the intermediate region, 10⁻¹—3 MPM. A metal-non-metal transition or, at lower temperatures, a phase separation takes place in the 3–7 MPM concentration range. We give a simplified theory of the Mott transition for these solutions and explore the inter-relation of the Mott transition, the observed metal-non-metal transition, and the phase separation. The metallic range extends from 7 MPM to saturation at 15 or 20 MPM in the concentrated solutions; we propose a fused-salt-like structure for this region. Suggestions are made for future research.