My interests focus on the structural, electronic and thermodynamic stability of inorganic crystalline solids, and how their behavior is affected by high pressure and temperature. These interrelated properties are particularly relevant to transformations between mineral phases, as pressure- and temperature-induced changes in minerals and rocks dictate the structure and dynamics of Earth’s interior and provide information on the evolution of our planet. High pressures and temperatures not only lead to changes in crystal structure, but can also result in changes in electronic state, leading to the modification of transport and other physical properties.
Most mineral systems exist in nature as solid solutions and are inherently complex with respect to composition. Therefore, in addition to studies of natural samples, a great deal of information can be gained by laboratory studies of pure end members and model systems. Investigations into the physics and chemistry of minerals take advantage of x-ray diffraction and spectroscopy facilities at the Advanced Photon Source at nearby Argonne National Laboratory. Experiments are supported by computational and theoretical work at various levels of sophistication, from empirical potential models and qualitative orbital techniques to ab-initio methods employing pseudopotential-based or all-electron codes.
1. Brownsberger, K.; Ahart, M.; Somayazulu, M.; Park, C.; Gramsch, S.A.; Hemley, R.J. “X-ray Diffraction, Lattice Structure and Equation of State of PdHx and PdDx to Megabar Pressures.” J. Phys. Chem. C 2017, 121, 27327-27331.
2. Wilfong, B.; Ahart, M.; Gramsch, S.A.; Stock, C.; Li, X.; Luo, H.; Hemley, R.J. “High P-T Raman Study of Transitions in Relaxor Multiferroic Pb(Fe0.5Nb0.5)O3.” J. Raman Spect. 2016, 47, 227-232.
3. Kyono, A.; Gramsch, S.A.; Nakamoto, Y.; Sakata, M.; Kato, M.; Tamura, T.; Yamanaka, T. “High-Pressure Behavior of Cuprospinel CuFe2O4 : Influence of the Jahn-Teller Effect on the Spinel Structure.” Am. Mineral. 2015, 100, 1752-1761.
4. Yamanaka, T.; Kyono, A.; Nakamoto, Y.; Kharlamova, S.; Struzhkin, V.V.; Gramsch, S.A.; Mao, H.-k.; Hemley, R.J. “A New Structure of High-Pressure, Body-Centered Orthorhombic Fe2SiO4.” Am. Mineral. 2015, 100, 1736-1743.
5. Ahart, M.; Karandikar, A.; Gramsch, S.A.; Boehler, R.; Hemley, R.J. “High P-T Brillouin Scattering Study of H2O Melting to 26 GPa.” High Pressure Research 2014, 34, 327-336.
6. Loubeyre, L.; Ahart, M.; Gramsch, S. A.; Hemley, R.J. “Density Dependence of Dynamical Heterogeneity in Fluid Methanol.” J. Chem. Phys. 2013, 138, 174507.
A.B. : Augustana College
M.S. : University of Washington
Ph.D. : University of Chicago
Postdoctoral : Geophysical Laboratory, Carnegie Institution of Washington