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Crystallography of new materials for clean energy production and the switch to a hydrogen based economy
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Dunn, Iain, (Researcher in physics) (2012) Crystallography of new materials for clean energy production and the switch to a hydrogen based economy. PhD thesis, University of Warwick.
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WRAP_THESIS_Dunn_2012.pdf - Submitted Version Download (7Mb) | Preview |
Official URL: http://webcat.warwick.ac.uk/record=b2623311~S1
Abstract
New energy materials have been investigated, including hydrogen storage materials and
dilute nitride semiconductors. The two potential hydrogen storage materials to have been
investigated are di-sodium amide borohydride (Na2NH2BH4) and lithium sodium
borohydride (LiNaBH4). Additionally, the homoepitaxial growth of InNSb and GaNSb across
a range of growth temperatures and rates has been examined and the effect of annealing
GaNSb layers grown on GaAs has also been studied.
It has been shown that Na2NH2BH4 undergoes a first order phase transition between a low
temperature orthorhombic phase and a high temperature cubic phase. There is a large
coexistence region between the two phases of -10°C to 70°C. The relative percentages of
each of these phases in this region are dependent on whether the sample is been heated or
cooled and the rate of change of the temperature, leading to a discrepancy in the overall
volume of the sample between heating and cooling. It has also been proved that there is a
metastable cubic phase of the sample that is seen when this material is first formed and
cooled.
Phase pure samples of LiNaBH4 have been synthesised from mixtures of sodium
borohydride and lithium borohydride, with varying amounts of lithium inclusion. This
lithium inclusion has resulted in some disorder in the sodium borohydride structure of the
samples up to temperatures of 200°C, which disorder is increased as the amount of lithium
increases. The inclusion of lithium has reduced the hydrogen desorption temperature by
c.a.10% from 550°C for pure sodium borohydride to 504°C for the sample with the most
lithium inclusion.
Both InNSb and GaNSb exhibit a linear relationship between growth temperature and
amount of nitrogen inclusion, with both more nitrogen being included and a greater
maximum growth temperature seen in the GaSb-based material. In both types of material
higher growth rates have resulted in less nitrogen inclusion at a given temperature. It has
been shown that the increased amount of nitrogen inclusion has improved the quality of
the grown layer.
Annealing of hetroepitaxially grown GaNSb has increased the amount of substitutional
nitrogen in these layers by allowing interstitial nitrogen to diffuse on to the crystallographic
B site of the material, at higher temperatures this effect has been reversed. Increased
nitrogen incorporation has resulted in a reduction in the crystal quality of these layers,
differing from the effects seen in the homoepitaxial layers.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QD Chemistry T Technology > TP Chemical technology |
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Library of Congress Subject Headings (LCSH): | Crystallography, Materials -- Technological innovations, Energy storage -- Materials, Hydrogen as fuel -- Research | ||||
Official Date: | October 2012 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Physics | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Thomas, Pam A. | ||||
Extent: | xiv, 146 leaves : illustrations, charts. | ||||
Language: | eng |
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