The structure of polaronic electron cavities in lithium–ammonia solutions

Abstract

Neutron diffraction has been used in conjunction with isotopic substitution of deuterium for hydrogen to study the structure of lithium–ammonia solutions, at concentrations spanning the metal–nonmetal transition. Detailed analysis and visualization of our experimental data has been carried out via iterative refinement of a three-dimensional molecular model, allowing us to obtain unique insight into the formation of polaronic electron cavities in the solutions. At low electron concentrations the solutions are nonmetallic, and the ammonia molecules are orientated around cavity centres to form Bjerrum-type defects. As the electron content is increased, the solutions become metallic, and we find evidence of percolation channels through the solvent. The dissociated electrons therefore play an active role in determining the structure of these solutions, and serve to disrupt the hydrogen bonding present in liquid ammonia.