Martin C. Wilding
<M.Wilding@shu.ac.uk>

Martin Wilding completed his first degree at Derbyshire College of Higher Education (now the University of Derby) and completed a PhD at the University of Edinburgh in 1990. He has considerable research experience and uses advanced diffraction techniques and novel sample environments to study materials under extreme conditions. His interests include the structure and glass and liquid structure including novel glass forming liquids and molten salts. He is currently a Research Associate at the Materials and Engineering Research Institute, Sheffield Hallam University.


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Carbonate network formation in ultra-high pressure glasses
Martin C. Wilding*1, Yoshio Kono2 Mark Wilson3, Paul A. Bingham1, Richard A. Brooker4
and John B. Parise5
1Materials and Engineering Research Institute, Sheffield Hallam University, Howard Street Sheffield S1 WB UK

2HPCAT, Geophysical laboratory, Carnegie Institute of Washington, 9700 South Cass Avenue,
Argonne, Illinois, 60439 USA

3Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, OX1 3QZ UK
4School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, U.K
5Department of Geosciences and Department of Chemistry, Stony Brook University,
Stony Brook, NY 11794-2100, USA

The influence of pressure on the structure and structural properties of glasses is of interest to scientists from a wide range of disciplines and there have been many recent studies that have investigated the evolution of traditional network-forming glasses with pressure. The influence of pressure on more exotic glass-forming systems remains to be explored however, and in this contribution we will present the results of an ultra-high pressure X-ray diffraction study of a pure carbonate glasses 45GPa.

Carbonate glasses are rare but were first reported in a pioneering study by Eitel and Skaliks in 1929. Carbonate glass can be formed in the system K2CO3-MgCO3 using high pressure synthesis techniques and sufficiently large amounts of glass can be produced for high pressure diffraction measurements. In situ X-ray diffraction data for these glasses was obtained using the energy dispersive technique at beamline 16-BM-B, High Pressure Collaborative Access Team (HPCAT) at the Advanced Photon Source (APS). The glass samples we contained within a newly-developed, double stage Paris-Edinburgh large volume press, this has a second stage of diamond anvils that enable high pressures to be achieved. These combined techniques enable amorphous diffraction data to be collected for scattering vectors of up to 14Å-1 for pressures as high as 44GPa.

The diffraction data obtained for the carbonate glasses shows significant changes in the amorphous structure as pressure is applied. This is illustrated in figure 1, which shows the total structure factor for the K-Mg carbonate glass. There is the development of a shoulder, at ~3 Å-1, to the first peak in diffraction pattern which progressively increases in intensity as pressure increases and which forms the dominant peak at the maximum pressure of 44GPa. There are also changes at higher Q that suggest changes in the short-range order of the carbonate glass. State-of-the-art molecular dynamics simulations, using the methodology of flexible anions and fluctuating change, provides the opportunity to interpret these changing structures. These simulations suggest that whilst the ambient pressure structure that is characterised by molecular carbonate anions, the higher pressure structure reflects formation of a corner-shared tetrahedral carbonate network. This has also been reported for pure CO2.