The metal-insulator transition and the phase transition in metal-ammonia solutions

The ground state of impurity metal (sodium) atoms in liquid ammonia close to the solvated state of the free electrons is considered. It is shown that the critical solubility point lying on the metal side of the metal-insulator transition is determined by the Coulomb interaction between the ions and electrons in the overlapping impurity states, classically accessible spheres of which form an infinite percolation cluster. The percolation conductivity via the impurity states is estimated. The estimate agrees with the experimental data near the critical solubility point.