The structure of Li and Na Phosphate oxynitride glassy electrolytes

In this proposal we will evaluate the structure of Li and Na phosphate glasses where oxygen has been partly substituted by nitrogen. This work is developed form a rapid access proposal, undertaken and GEM and work completed at the SNS (NOMAD) and forms part of a large-scale project that is focussed on developing these materials as solid electrolytes. Nitrogen can be Incorporated into phosphate glasses when exposed to ammonia (ammonolysis) and after nitridation the glasses show enhanced properties including improved mechanical performance. Importantly from a glass structure perspective these glasses have “invert” structures with isolated coordination polyhedra and extensive intermediate range order in. In this proposal, we will study two base compositions, a metaphosphate (MPO3) and M4P2O7 (M=Li or Na) to compare and contrast the medium range ordering. Molecular dynamics simulations of these systems is show development of ordering at the intermediate length scale and development (in the simulations) of small angle features, not accessed in the study completed at GEM. Therefore we will evaluate the development of intermediate range ordering and small angle features using the full Q range available at NIMROD. We will study 12 samples and evaluate structures as a function of nitrogen and also as a function of the two alkali cations, lithium and sodium.