My research investigates phase stability, electronic transitions, and atomic structure at high pressure. I am particularly interested in iron-bearing materials, silicate glasses and liquids, and the ways materials transform during rapid compression or heating.
Materials at extreme conditions
Iron in the mantle and core
Iron’s electronic state provides a connection between mineral chemistry and physical properties. A spin crossover changes the arrangement of electrons without necessarily producing an obvious change in crystal structure. This raises questions about how iron is distributed between mantle minerals and how their properties evolve with depth.
In a pyrolitic model of the lower mantle, we investigated the relationship between iron spin crossovers, oxidation state, and partitioning between silicate perovskite and ferropericlase. Related work on iron carbides examined carbon alloying as a possible explanation for the unusual elastic properties of Earth’s inner core. These experiments test candidate materials and mechanisms; they do not uniquely determine the core’s composition.
Mössbauer spectroscopy complements diffraction by probing the local environment and electronic state of iron. MossA supports the fitting of conventional and synchrotron energy-domain spectra used in this type of work.
Selected publications:
- Prescher et al. (2014). The effect of Fe spin crossovers on its partitioning behavior and oxidation state in a pyrolitic Earth’s lower mantle system. Earth and Planetary Science Letters.
- Prescher et al. (2015). High Poisson’s ratio of Earth’s inner core explained by carbon alloying. Nature Geoscience.
Structure of glasses and liquids
Glasses and liquids lack the repeating crystal structures that make conventional crystallography possible. Their diffuse X-ray scattering nevertheless contains information about interatomic distances, coordination, and the organisation of their atomic networks. I use total scattering and pair distribution functions to investigate how these structures respond to compression.
Our measurements of silica glass extended structural observations to 172 GPa and indicated a continuous increase in silicon–oxygen coordination beyond six at high pressure. In collaborative work on liquid silicates, we combined diffraction experiments and atomistic simulations to investigate structural evolution under conditions relevant to Super-Earth interiors. Glasses provide useful comparisons for liquids, but differences in temperature and density must be considered when drawing that connection.
Glassure supports the analysis from measured scattering patterns to structure factors and pair distribution functions. Background subtraction, normalization, and the measured momentum-transfer range are central to interpreting the resulting local structure.
Selected publications:
- Prescher et al. (2017). Beyond sixfold coordinated Si in SiO₂ glass at ultrahigh pressures. Proceedings of the National Academy of Sciences.
- Morard et al. (2024). Structural evolution of liquid silicates under conditions in Super-Earth interiors. Nature Communications.
Time-resolved high-pressure experiments
The path to a high-pressure state matters as well as the final pressure and temperature. Rapid compression and pulsed heating allow us to investigate how transformations proceed, whether intermediate states form, and how quickly a material responds.
At the European XFEL, short X-ray pulses make it possible to collect diffraction snapshots during these changes. I have contributed to the development of diamond anvil cell experiments using megahertz pulse trains and to collaborative studies of materials under dynamic compression. Work on liquid carbon, for example, used in situ diffraction to constrain its atomic structure at extreme pressure and temperature.
Selected publications:
- Liermann et al. (2021). Novel experimental setup for megahertz X-ray diffraction in a diamond anvil cell…. Journal of Synchrotron Radiation.
- Kraus et al. (2025). The structure of liquid carbon elucidated by in situ X-ray diffraction. Nature.
Experiments and analysis
Reliable structural interpretation begins with detector calibration, masking, and integration. Dioptas makes these steps available during an experiment, so that changes in diffraction patterns can inform the next measurement. For disordered materials, recent collaborative work demonstrated quantitative total scattering and pair distribution functions from individual approximately 30-femtosecond XFEL pulses, extending local-structure measurements to much shorter timescales.
Connecting measured volumes to pressure, compressibility, and thermal expansion also requires a choice of equation of state and pressure calibration. Peritheos provides a way to compare these models and their published material parameters while retaining their source references. This helps make the assumptions behind comparisons between experiments explicit, including the distinction between interpolation within measured conditions and extrapolation beyond them.
Selected publications:
- Prescher and Prakapenka (2015). DIOPTAS: a program for reduction of two-dimensional X-ray diffraction data and data exploration. High Pressure Research.
- Sapnik et al. (2025). High-quality ultra-fast total scattering and pair distribution function data using an X-ray free-electron laser. IUCrJ.