Structure of a metallic solution of lithium in ammonia

Neutron diffraction has been used in conjunction with isotopic substitution to measure the structure of a saturated metallic solution of lithium in am monia (21 mole % metal). This concentration of solution is of particular in terest due to its high electrical conductivity, low density, and position a bove a deep pseudoeutectic. We find that the solution is highly structured over both shea and intermediate length scales. The local coordination aroun d each Lif cation consists of a well defined solvation shell containing an average of 3.5 ammonia molecules. These molecules direct their dipole momen ts away from the cation, and are undistorted relative to the pure solvent. The delocalized electrons are therefore fully dissociated from the cations. A strong first diffraction peak at 0.97 Angstrom(-1) is seen in both Li+- and N-centered correlations, and provides evidence of intermediate-range or der in the solution.