Dissertation
CHEMISTRIES OF HYDROGEN-SULFUR COMPOUNDS, LAYERED MATERIALS AND NITROGEN-RICH AZIDE UNDER HIGH PRESSURE
Doctor of Philosophy (PhD), Washington State University
01/2018
Handle:
https://hdl.handle.net/2376/118479
Abstract
Pressure results in dramatic changes in the chemical bonding of molecules as the compression energy rivals to those constituent bond energies. We have studied the pressure-induced chemistries of hydrogen-sulfur compounds (H2S, D2S, H2-S mixtures). We found the symmetrization of proton in H2S and D2S, as the pressure brings the molecules closer to each other, as previously observed in “polymeric” Ice X with hydrogen at the center of two nearby oxygen atoms. Under strong lights, however, H2S decomposes to sulfur above 30 GPa. The photochemical reactivity of sulfur, in turn, allows us to synthesize novel compound (H2S)2H2 at 4 GPa by illuminating laser lights on H2-S mixtures. Interestingly, this newly synthesized compound has the same stoichiometry as H3S, a record high Tc (203 K) superconductor formed by compressing H2S above 150 GPa.
Transition metal sulfides/oxides typically crystallize into layered structures with strongly anisotropic chemical bondings; covalent within the layers and weak van der Waals in between the layers. To investigate the effect of compressive shear on the layer structure, we have investigated (WS2) up to 60 GPa and MoO3 up to 100 GPa. The results show that WS2 in non-hydrostatic condition undergoes an iso-structural phase transition at 37 GPa, which accompanies the metallization. In contrast, no transition is observed in hydrostatic helium pressure medium showing a strong shear effect on the transition. Similarly MoO3 in non-hydrostatic condition undergoes a series of transitions from MoO3-I to MoO3-II at 10 GPa, and then to MoO3-III at 30 GPa, whereas MoO3-I directly transforms to MoO3-III at 37 GPa, bypassing MoO3-II in hydrostatic conditions. These results indicate that small helium atoms diffuse in between the layers and thereby block the propagation of shear-induced deformation.
Nitrogen-rich materials are considered as high energy density materials and are often subjected to synthesis of more extended forms of nitrogen at high pressures. Therefore, we have investigated hydrazinium azide (N2H5+N3-) to 68 GPa and found that it transforms to a new form of nitrogen-rich allotrope, N8, above 40 GPa, which was predicted to be stable at ambient conditions. However, N8 decomposes to epsilon-N2 upon unloading pressure below 25 GPa.
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Details
- Title
- CHEMISTRIES OF HYDROGEN-SULFUR COMPOUNDS, LAYERED MATERIALS AND NITROGEN-RICH AZIDE UNDER HIGH PRESSURE
- Creators
- Sakun Duwal
- Contributors
- Choong-Shik Yoo (Advisor)Choong-Shik Yoo (Committee Member)Ursula M Mazur (Committee Member)David Y Lee (Committee Member)Yi Gu (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Department of Chemistry
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 202
- Identifiers
- 99900581713401842
- Language
- English
- Resource Type
- Dissertation