Structural insights into the lithium amide-imide solid solution

Research output: Contribution to journalArticlepeer-review

Authors

Colleges, School and Institutes

External organisations

  • University of Oxford
  • ISIS Facility, Rutherford Appleton Laboratory

Abstract

Solid solutions of lithium amide (LiNH2) and lithium imide (Li2NH) are present during ammonia decomposition catalysis by lithium imide and hydrogen storage and release reactions in the lithium amide–lithium hydride composite. As such, they are important materials in facilitating the use of hydrogen as a sustainable energy store. In order to understand the properties of these solutions, a series of samples spanning the full stoichiometry range of the solid solution between lithium amide and lithium imide were synthesized. Powder diffraction measurements showed that a nonstoichiometric cubic phase isostructural to the high-temperature phase of lithium imide was observed in all of the samples. In average stoichiometry values close to lithium amide, incomplete formation of a solid solution was observed, with tetragonal lithium amide observed in addition to the cubic nonstoichiometric phase. In analysis of neutron diffraction data, the variable stoichiometry in the structure was modeled using a “golf-ball” of scattering density around the nitrogen atom. This analysis revealed a greater degree of disorder in hydrogen distribution in the nonstoichiometric samples compared with lithium imide. Raman spectroscopy indicated that amide and imide groups in stoichiometric and nonstoichiometric environments can be differentiated by the frequency of the N–H stretch, with distinct bands observed for both amide and imide N–H stretches in both environments.

Details

Original languageEnglish
Pages (from-to)12010−12017
Number of pages8
JournalThe Journal of Physical Chemistry A
Volume121
Issue number22
Publication statusPublished - 10 May 2017