The heavy alkaline earth hydrides consist of the Group II (alkaline earth metal) hydrides, namely CaH2, SrH2, and BaH2, which adopt the cotunnite-type structure at ambient pressure and temperature conditions. There has been much recent research interest in these compounds; in the past decade numerous experimental and theoretical studies exploring the hydrides in both applied and fundamental respects have been added to the literature. The present work constitutes a study of the heavy alkaline earth hydrides subjected to extreme pressure conditions (at ambient temperature). Specifically, pressure-dependent angle-dispersive powder x-ray diffraction and Raman spectroscopy experiments, as well as first-principles calculations, have been carried out to explore the structural stability, compressibility, and optical phonon spectra of the heavy alkaline earth hydrides. To complement the work on the hydrides, a companion study on BaF2---a structural analogue---is presented, as well as a description of some selected experimental techniques used to carry out the research. The powder x-ray diffraction results reveal that all of the heavy alkaline earth hydrides undergo a pressure-induced, first-order structural phase transition. The proposed Ni2ln structure for the high-pressure phase is based on both the results of first-principles calculations and an isostructural comparison with BaF2. The transition pressures and the proposed high-pressure structure are corroborated by the results of the Raman spectroscopy measurements. Where applicable, equation of state parameters from both the experimental and theoretical studios are reported, and a comparison of these respective parameters at ultra-high pressures (greater than 50 GPa) suggests that the experimentally observed bulk moduli are overestimated due to the presence of non-hydrostatic pressure conditions.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/29845 |
| Date | January 2009 |
| Creators | Smith, Jesse S |
| Publisher | University of Ottawa (Canada) |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 161 p. |
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