This work presents an in-depth study of the crystal structures and hydrogen sorption potential of the Li - N - H and Li - Na - N - H systems. The structures of the materials have been studied using X-ray and neutron diffraction, Raman spectroscopy and inelastic neutron scattering. The behavior of the materials during heating was studied using variable temperature X-ray diffraction, intelligent gravimetric analysis in conjunction with neutron diffraction, intelligent gravimetric analysis combined with mass spectrometry and differential scanning calorimetry. The role of cation disorder in the Li - N - H (D) system has been explored, indicating that crystallographic ordering of the Li<sup>+</sup> ions within lithium amide and lithium imide significantly affects the hydrogen sorption properties of the materials. Order-disorder transitions were observed both during hydrogen desorption from ordered LiNH<sub>2</sub> and during deuterium adsorption on ordered Li<sub>2</sub>ND. Such transitions were not observed in disordered samples of the materials. The intrinsic disorder and the stoichiometry of Li - N - H(D) materials was shown to depend strongly on the techniques used during their synthesis. Studies regarding the synthesis, crystal chemistry and decomposition properties of the mixed Li / Na amides are presented. Two distinct mixed Li / Na amides of formulae Li<sub>3</sub>Na(NH<sub>2</sub>)<sub>4</sub> and LiNa<sub>2</sub>(NH<sub>2</sub>)<sub>3</sub> were observed in the LiNH<sub>2</sub> / NaNH<sub>2</sub> phase space. Na was also seen to be soluble in LiNH<sub>2</sub>, forming sodium-doped LiNH<sub>2</sub> . Li<sub>3</sub>Na(NH<sub>2</sub>)<sub>4</sub> and Na-doped LiNH<sub>2</sub> were found to exhibit significant cation non-stoichiometry, whereas LiNa<sub>2</sub>(NH<sub>2</sub>)<sub>4</sub> was shown to exist as a line phase material. Thermogravimetric and calorimetric studies of the mixed Li / Na amides suggested that these materials decompose primarily with loss of H<sub>2</sub>.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:509983 |
| Date | January 1999 |
| Creators | Lowton, Rebecca L. |
| Contributors | Edwards, Peter P. |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:df7b324d-c33d-4265-91cb-0555c3a10bec |
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