Creation energy of ionic defects in water ice studied with diffuse neutron scattering

Water is one of nature’s most familiar materials yet it is also one of the most unusual. From lowering its density upon freezing to being an almost universal solvent there are many properties that are peculiar to water. In its solid phase the oxygen ions sit at well-ordered crystalline sites with hydrogen ions sitting at one-of-two possible sites between neighboring oxygen. The structural configuration is described by the Bernal-Fowler “ice rules” where each oxygen bonds covalently with two nearby hydrogen ions and forms hydrogen-bonds with two further away hydrogen ions. By mapping the hydrogen displacement from the center of the O-O bond onto an Ising vector it has been shown that ice can be modelled using an emergent electromagnetic theory. Here we present diffuse neutron scattering results from heavy water ice, D₂O, that are fitted with a large-N electromagnetic model from Isakov et al. allowing us to find the correlation length between ionic defects in water ice, i.e. H₃O⁺ and OH^-, and from this deduce the formation energy of the defect pair.