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Title: Structural and thermogravimetric studies of alkali metal amides and imides
Author: Lowton, Rebecca L.
ISNI:       0000 0004 2681 9794
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 1999
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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+ 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 LiNH2 and during deuterium adsorption on ordered Li2ND. 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 Li3Na(NH2)4 and LiNa2(NH2)3 were observed in the LiNH2 / NaNH2 phase space. Na was also seen to be soluble in LiNH2, forming sodium-doped LiNH2 . Li3Na(NH2)4 and Na-doped LiNH2 were found to exhibit significant cation non-stoichiometry, whereas LiNa2(NH2)4 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 H2.
Supervisor: Edwards, Peter P. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Inorganic chemistry ; alkali metal amides ; alkali metal imidies ; gravimetric analysis ; scanning calorimetry ; x-ray diffraction ; neutron diffraction