This thesis describes the effect of pressure on crystal structures that are in some way unusual. The aim was to investigate whether pressure could be used to force these ‘structural oddities’ to conform to more conventional behaviour. In many cases pressure-induced phase transitions were observed, and the driving forces of these are considered. L-serine monohydrate crystallises with layers of hydrogen bonded serine molecules. Layers are linked together by H-bonds from the donor atoms of water molecules. The orientation of the water molecules between the layers is uncommon for other layered hydrates in the CSD. A single crystal of serine hydrate undergoes a pressure-induced phase transition at 5 GPa, which is characterised by a rotation of the water molecules to an orientation which is more frequently observed. PIXEL calculations show that the transition is driven by the PV term in the equation G = U - TS + PV. An attempt to reproduce the transition in another layered hydrate with a similar topology was partially successful in the compression of S-4-sulfo-L-phenylalanine monohydrate, which undergoes a similar phase transition at 1 GPa. Methyl 2-(9H-carbazol-9-yl)benzoate crystallises unusually with eight molecules in the asymmetric unit (Z’ = 8). Compression of a single crystal results in a phase transition at ca. 5 GPa to give a Z’ = 2 polymorph. The PV term is an important contributor to the driving force of the transition. The geometries of the molecules in phase-II are significantly less stable than in phase-I, and as pressure is released on phase-II the need to adopt a more stable molecular conformation eventually outweighs the PV advantage. The Z’ = 8 structure is eventually re-established at 4.6 GPa. This work illustrates how low Z’ polymorphs of the same structure are not always the thermodynamically more stable forms. When recrystallised in situ from a 4:1 by volume solution of methanol and ethanol, a new polymorph of salicylamide is obtained at 0.2 GPa. The ambient pressure phase appears in the CSD to contain a number of abnormally short H…H contacts. We find this model to be incorrect, and have re-determined the structure to find no short H…H contacts. PIXEL and DFT calculations indicate that the high-pressure polymorph is favoured over the ambient phase by the PV term, the zero point energy and entropy. Low completeness that often occurs as a result of shading from the high-pressure cell was improved by the inclusion of multiple crystals within the sample chamber. Bianthrone changes colour from yellow to green on grinding, though this does not occur when subjected to hydrostatic pressure to 6.5 GPa. There is, however, a subtle colour change from bright yellow to dark orange as pressure is applied, and it is likely that this is caused by changes in the - stacking distances. This work highlights how a system can react differently to hydrostatic and non-hydrostatic conditions.

The application of extreme conditions offers a general route for the synthesis of materials under equilibrium conditions. By finely tuning the thermodynamic variables of pressure and temperature one can manipulate matter on an atomic scale, creating novel compounds or changing the properties of existing materials. In particular, the study of hydrogen and hydrogen compounds has attracted the attention of researchers in the past. Although hydrogen readily reacts with many elements at ambient conditions, there is a significant “hydride gap” covering the d-metals between the Cr-group and Cu-group elements. At elevated pressures however, the chemical potential of hydrogen rises steeply. At sufficient pressures, hydrogen overcomes the dissociation barrier at the metal surface and atomic hydrogen diffuses into the metal, usually occupying interstitial sites in the host matrix. These interstitial hydrogen alloys can exhibit interesting physical properties, such as modified crystalline structures, different compressibility, altered microstructure (nanocrystallinity), hydrogen mediated superconductivity or potential hydrogen storage capabilities. Furthermore, theory predicts that hydrogen confined in a host matrix might undergo the elusive transition to a metallic groundstate at considerably lower pressures than pure hydrogen. Most d-metals have been found to exhibit hydride phases at extended conditions of pressure and temperature. However, besides rhenium, the 6th row metals between tungsten and gold, as well as silver, have not or only very recently been found to form bulk hydrides. In the course of this PhD-thesis, several of the missing metalhydrides were successfully synthesized in the diamond anvil cell and characterized by in-situ x-ray diffraction using synchrotron radiation.

<p>Hydrogen has been called the fuel of the future, and as it’s non- renewable counterparts become scarce the economic viability of hydrogen gains traction. The potential of hydrogen is marked by its high mass specific energy density and wide applicability as a fuel in fuel cell vehicles and homes. However hydrogen’s volume must be reduced via pressurization or liquefaction in order to make it more transportable and volume efficient. Currently the vast majority of industrially produced hydrogen comes from steam reforming of natural gas. This practice yields low-pressure gas which must then be compressed at considerable cost and uses fossil fuels as a feedstock leaving behind harmful CO and CO2 gases as a by-product. The second method used by industry to produce hydrogen gas is low pressure electrolysis. In comparison the electrolysis of water at low pressure can produce pure hydrogen and oxygen gas with no harmful by-products using only water as a feedstock, but it will still need to be compressed before use. Multiple theoretical works agree that high pressure electrolysis could reduce the energy losses due to product gas compression. However these works openly admit that their projected gains are purely theoretical and ignore the practical limitations and resistances of a real life high pressure system. The goal of this work is to experimentally confirm the proposed thermodynamic gains of ultra-high pressure electrolysis in alkaline solution and characterize the behavior of a real life high pressure system.</p> / Dissertation

Trace elements are highly fractionated during large-scale melting associated with planetary differentiation events. The resulting partition coefficients are used to constrain a range of geological processes and are known to be influenced by pressure, temperature, and compositional changes in crystalline structures. Although recent studies have shown that melt compositional changes affect the partitioning of trace elements, the degree to which these ratios are influenced by alterations in the melt structure, especially with increasing pressure, is poorly constrained due to the difficulty of collecting structural information on bonding environments in situ. A basic understanding of how these elements are incorporated in silicate melts is critical to interpreting early planetary differentiation and crust forming events. This thesis presents results from both x-ray diffraction and absorption techniques on trace element (Y, Zr, Lu and Nd) incorporation in silicate melt structures. The structure of two rare Earth element doped model end member silicate liquids, a highly polymerised haplogranite (Si- Al-Na-K-O) and a less polymerised anorthite-diopside (Si-Al-Mg-Ca-O), have been studied. The results are the first to identify trace rare Earth element (REE) incorporation in silicate melts at high pressure using x-ray diffraction techniques. The local melt structure around Y and Zr in a highly polymerised haplogranite has been studied using x-ray absorption spectroscopy up to 8GPa and 1650 K. Both elements appear to adopt 8-fold coordination within the melt structure with no variation over the pressure range studied. This was also found for the Lu bonding environment in the same composition where the coordination number of Lu-O was found to be 8, with a bond distance rLu-O = 2:36A in the haplogranite melt. At low pressures, < 5GPa, the bonding environment of Lu-O was found to be dependent on composition with coordination decreasing to CNLu-O = 6 and rLu-O = 2:29A in the anorthite-diopside melt. This compositional variance in coordination number at low pressure is consistent with observations made for Y-O in glasses at ambient conditions and is coincident with a dramatic increase in the partition coefficients previously observed for rare Earth elements (REE) with increasing melt polymerisation. However, an abrupt change in both Lu-O coordination and bond distance is observed at 5GPa in the anorthite-diopside melt, with CNLu-O increasing from 6 to 8-fold and rLu-O from 2.29 to 2.39A. This occurs over a similar pressure range where a reduction in the reported heavy REE partition coefficients is observed. X-ray diffraction experiments up to 60GPa and 2000K have also been performed on the incorporation of the larger light REE, Nd, in basaltic-like melts. The results presented show that incorporation within the anorthite-diopside composition is dependent on the size of the REE. Nd-O initially shows the same 6-fold coordination as Lu-O at ambient conditions, although the change to 8-fold coordination appears to occur at considerably lower pressure between 1-2GPa. Coordination change in both cases can be attributed to collapse of the silicate network and an increase in the average number of available 'crystal like' sites in the liquid, with ionic radius of the REE controlling at which pressure the preference for these sites in the melt occurs. Published mineral-melt partition coefficients for Nd, with major mineral phases such as garnet, show very little variation with pressure, in contrast to Lu. The difference in structural incorporation of Lu and Nd in the melts presented in this thesis could explain this partitioning behaviour. Overall this thesis highlights that important structural changes of the trace element bonding environment in silicate melts occur with both compositional variation and pressure. Melt structural changes with pressure cannot be neglected in predictive models of trace element behaviour, and using a single melt term to normalise the effects of melt on trace element partitioning will not accurately predict partitioning behaviour at depth during magma formation or differentiation.

Under pressure small molecular systems exhibit a remarkable degree of polymorphism and unexpected behaviours. Two previously unexplored binary systems, those of niobium{hydrogen and water{oxygen, are explored and their phase diagrams mapped. In the case of water and oxygen, two hitherto unknown clathrate structures are found. A wide study of dense nitrogen at and above room temperature is also reported. The phase diagram of nitrogen is exceptionally complex for a single element and exhibits considerable metastability of phases. Current theoretical understanding of nitrogen has many disagreements with experimental observation. High quality structural data on various previously known phases are reported as well as a novel molecular phase. This new phase, λ-N2, has been studied using Raman spectroscopy and powder x-ray diffrraction. Combining experimental and theoretical results gives a layered structure with intermolecular interactions playing an important role and an apparently weakened intramolecular bond. The dissociation of the nitrogen triple bond is also examined. The amorphous η state is studied via Raman spectroscopy and optical and IR absorbance methods before laser heating at 255 GPa. After heating the sample becomes very much more transparent and shows signs that the nature of the bandgap has changed suggesting that the nitrogen may be in a crystalline atomic phase hitherto unknown. An effort to take nitrogen to considerably higher pressures is reported. A two stage diamond anvil cell was developed using focused ion beam micromachining. Although ultimately unsuccessful, to the author's knowledge this was the first ever attempt at designing such a system to be compatible with small molecular samples and Raman spectroscopy and various conclusions are as to how best to proceed with such developments.

The mechanism of high pressure-adapted growth in the deep-sea bacterium Photobacterium profundum SS9 is poorly understood. To gain further insights, two P. profundum SS9R mutants were investigated. FL23 (pbpra3229::m-Tn10) and FL28 (pbpra1039::m-Tn10) had been previously characterised as high pressuresensitive and pressure-enhanced, respectively. FL23 had a growth defect at atmospheric pressure but failed to show high pressure-adapted growth on solid agar. Pbpra3229 is 75 % identical to E. coli DiaA (stimulator of DNA replication and critical for the timely initiation of replication) and 45% identical to E. coli GmhA (essential for lipopolysaccharide core biosynthesis), which led to an investigation into whether either process was affected in FL23. However, the lipopolysaccharide of FL23 and its parent strain were identical, which suggests that Pbpra3229 is not a GmhA homologue. In contrast, the pbpra3229 and E. coli diaA genes were functionally interchangeable and both restored the timing of DNA replication in an E. coli diaA mutant. FL28 had growth and morphological defects at high pressure, but both phenotypes were exacerbated at atmospheric pressure. Pbpra1039 is 55% identical to E. coli SeqA, which is a negative regulator of DNA replication and also essential for timely initiation. Pbpra1039 was shown to be a functional homologue of E. coli SeqA, as pbpra1039 partially complemented the DNA replication defect of an E. coli seqA mutant. Combined, these findings provide evidence that Pbpra3229 is a DiaA homologue, whereas Pbpra1039 is a cold adapted SeqA homologue, and that both positive and negative regulation of initiation of DNA replication are essential for the ability of P. profundum SS9 to adapt to deep-sea conditions. A marine metagenomic library was also screened for clones that produced novel cell envelope polysaccharides and tools were developed to identify cell envelope polysaccharides in P. profundum SS9.

The work presented in this thesis investigates the behaviour of the Rashba semi-conductor BiTeI and of the topological insulator $\text{Bi}_2\text{Te}_3\,$ under pressure. Using Shubnikov-de Haas quantum oscillation measurements, the evolution of the Fermi surface of both materials was tracked as a function of pressure. At ambient pressure, two distinct quantum oscillation frequencies in BiTeI, corresponding to inner and outer Fermi surface orbits as a result of spin-splitting caused by the Rashba effect, were observed. Using a model Hamiltonian with a Rashba interaction term to model this system, experimental results were fitted to determine model parameters. Based on this model, carrier densities for the samples were calculated and there was good agreement with Hall effect measurements. The phase of the oscillations showed that both Fermi surfaces have a Berry phase of $\pi$ associated with them, consistent with theoretical predictions for a Rashba system. As pressure is applied, it was observed that the inner Fermi surface expands while the outer Fermi surface shrinks. Phase analysis of the oscillations showed deviations from the ambient pressure value, hinting at a topological transition. For $\text{Bi}_2\text{Te}_3\,$, we report the observation of two oscillation frequencies ($\sim 40$ T and $\sim 340$ T) at ambient pressures. Based on the angular dependence of the oscillation frequencies, phase analysis, and comparison against band structure from published ARPES results, it is deduced that the higher frequency oscillation corresponds to the surface state of $\text{Bi}_2\text{Te}_3$. Non-linear behaviour in the Hall measurement also suggests the presence of multiple bands, and a two-band model with parameters derived from quantum oscillation measurements is used to fit the experimental data. Under pressure, a slight decrease in the low field Hall coefficient and a new frequency appearing at $\sim 20$ kbar was observed. These may be signatures of a change in the Fermi surface of $\text{Bi}_2\text{Te}_3\,$ caused by an electronic topological transition.

No description available.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 131-142).

Alicyclobacillus acidoterrestris is a spore-forming food spoilage bacterium. Its spore is problematic to the juice industry because of its ability to grow in low pH environments and survive pasteurization processes. The purpose of this study was to investigate the effect of the non-thermal technology, high pressure homogenization (HPH) and the antimicrobial compound, dimethyl dicarbonate (DMDC), on inactivation of A. acidoterrestris, in a broth system. Vegetative cells and spores of five strains of A. acidoterrestris (N-1100, N-1108, N-1096, SAC and OS-CAJ) were screened for their sensitivity to HPH (0, 100, 200 and 300 MPa) in Bacilllus acidoterrestris thermophilic (BAT) broth. Strain SAC (most resistant) and OS-CAJ (least resistant) were further tested for their sensitivity to 250 ppm DMDC. This was followed by evaluation of combined effects of HPH and DMDC against strain SAC. Effects of HPHand DMDC treatment combinations (no DMDC, 250 ppm DMDC added 12 h before, 2 h before, immediately before, and immediately after 300 MPa HPH treatment) on spores of SAC over a 24-h period were evaluated. After all treatments, samples were serially diluted and surface plated onto BAT agar, and the populations were determined after incubation at 44 &degC for 48 h. All HPH and DMDC treatments significantly (P<0.05) inhibited growth of vegetative cells, spores were less affected by these treatments. HPH caused a 1-to 2-log reduction in vegetative cell populations at 300 MOa for four strains, but only about 0.5-log reduction of SAC strain. Spores of all five strains were not significantly reduced by HPH. DMDC also slowed growth of vegetative cells significantly. For vegetative cells of SAC and OS-CAJ, 250 ppm DMDC reduced the population by about 2 log whereas spore population was reduced by less than 0.5 log. The addition of DMDC together with HPH slightly enhanced the inactivation effect over a 24-h period as compared with treatment with HPH alone. These results demonstrate that HPH and DMDC show promise for aiding in control of growth of vegetative cells of A. acidoterrestris. However, neither treatment alone or in combination, is very effective against spores.