|dc.contributor.author||Storm, Christian Viktor||
|dc.description.abstract||Research at high pressures has revealed that the elemental metals, most of
which have simple crystal structures at ambient conditions such as face-centred
cubic, body-centred cubic, or hexagonal close-packed, transition to more complex
structures at high pressure. X-ray diffraction methods are well-suited to exploring
these complexities, providing detailed data on the structure of elements at high
pressure. In particular, this work focuses on studying the alkali metals K and
Rb with x-ray diffraction methods. These elements have been found to exhibit a
wealth of structural complexity such as the incommensurate host-guest structures
K-III and Rb-VI, or the orthorhombic Cmca phases of K-VI and Rb-VI.
To study these and other elements at high pressures, diamond anvil cells are
frequently used to compress the sample, as they allow for accurate structure
identification using x-ray diffraction and can reliably reach pressures of around
300 GPa. However, the study of elements at even higher pressures becomes
difficult using conventional diamond anvil cells which are prone to diamond failure
at these conditions. This has motivated the development of new DAC designs.
In particular, toroidal diamond anvil cells are a promising modification wherein
the diamond anvils are ‘sculpted’ to create a geometry able to achieve pressures
above 500 GPa.
This work initially investigates the behaviour of the light metals Mg and Al and
the alkali metals K and Rb, using conventional diamond anvil cell techniques.
The phase transitions of Mg and Al are discussed, with compression data up to
301 GPa and 236 GPa presented for Mg and Al, respectively. Equations of state
are fitted for each metal and the data are compared to other studies in the field.
In K and Rb, the static phase diagrams are extended up to 321 GPa and 264 GPa,
respectively. These studies observe significant changes in the compression curves
occurring between 0-100 GPa, where the various phase transitions of these metals
display a great variety of compressive behaviour. The predicted high-pressure
oC16→hP4 phase transition is observed and presented for the first time in Rb.
However, no analogous transition is seen in K in spite of theoretical predictions.
The design, manufacture, and implementation of toroidal diamond anvil cells
are subsequently detailed, including the specifics of focused ion beam milling.
Experiments on the strongly scattering elements W and Ce are then presented.
In W, the body-centred cubic phase remains stable up to the highest pressure
of 381 GPa, as expected. However, unanticipated changes in the sample pressure
environment demonstrate the complexity of performing toroidal diamond anvil
cell experiments. In Ce, an apparent shift in the compression curve was observed
between 200-250 GPa, accompanied by decreasing c/a ratio in the body-centred
tetragonal phase above 250 GPa. The cause of the change in compressive
behaviour is unknown, but the c/a ratio decline is found to agree with theoretical
Finally, results from toroidal diamond anvil cell investigations of Rb are presented
along with the challenges of studying light and highly reactive elements using
toroidal diamond anvil cells. A highest pressure of 272 GPa is recorded from
Raman spectroscopy measurements of the diamond.||en
|dc.contributor.sponsor||Engineering and Physical Sciences Research Council (EPSRC)||en
|dc.publisher||The University of Edinburgh||en
|dc.relation.hasversion||C. V. Storm, J. D. McHardy, S. E. Finnegan, E. J. Pace, M. G. Stevenson, M. J. Duff, S. G. MacLeod, and M. I. McMahon, Behavior of rubidium at over eightfold static compression, Physical Review B 103, 224103 (2021).||en
|dc.relation.hasversion||S. G. Macleod, D. Errandonea, G. A. Cox, H. Cynn, D. Daisenberger, S. E. Finnegan, M. I. McMahon, K. A. Munro, C. Popescu, and C. V. Storm, The phase diagram of Ti-6Al-4V at high-pressures and high-temperatures, Journal of Physics: Condensed Matter 33, 154001 (2021)||en
|dc.relation.hasversion||S. E. Finnegan, E. J. Pace, C. V. Storm, M. I. McMahon, S. G. MacLeod, H.-P. Liermann, and K. Glazyrin, High-pressure structural systematics in samarium up to 222 GPa, Physical Review B 101, 174109 (2020).||en
|dc.relation.hasversion||E. J. Pace, S. E. Finnegan, C. V. Storm, M. Stevenson, M. I. McMahon, S. G. MacLeod, E. Plekhanov, N. Bonini, and C. Weber, Structural phase transitions in yttrium up to 183 GPa, Physical Review B 102, 094104 (2020).||en
|dc.relation.hasversion||S. E. Finnegan, C. V. Storm, E. J. Pace, M. I. McMahon, S. G. MacLeod, E. Plekhanov, N. Bonini, and C. Weber, High-pressure structural systematics in neodymium up to 302 GPa, Physical Review B 103, 134117 (2021).||en
|dc.subject||diamond anvil cell||en
|dc.subject||toroidal diamond anvil cell||en
|dc.title||Structural investigations of elemental metals at multi-megabar pressures using toroidal diamond anvil cells||en
|dc.type||Thesis or Dissertation||en
|dc.type.qualificationname||PhD Doctor of Philosophy||en