Research

Impact Mineralogy

Impact cratering is recognized as an important process in the formation and evolution of planetary bodies, which relies upon complex aggregation, collision and ejection processes between planetesimal materials and planetary surfaces. Impactites and meteorites provide a record of these high-impact processes, where we can determine the conditions of the impact and provide experimental constraint for the models of planet formation from the primordial solar nebular. Our knowledge of impact processes has significantly improved over the past decades, in particular through the combination of field studies, experiments and numerical simulations. The dynamic and highly heterogeneous nature of the impact process can be observed on different length scales. Heterogeneities can be observed on the micron- to submicron scale with the formation of cracks, melt veins and aggregates of minerals that cannot coexist under equilibrium conditions.

We have participated in the development of fast pressure and temperature generation in a diamond anvil cell coupled with in situ characterization techniques, such as time-resolved synchrotron powder diffraction, in order to close this gap in experimental techniques. This fast compression technique enables us to follow the mineral transitions in real time as a function of loading path, peak pressure, peak pressure duration, unloading paths, and heating/cooling paths. With this new approach, we have been able to access the pressure and temperature conditions in long shock duration events, such as meteorite impacts, that cannot be constrained with standard experimental techniques.

Collaborators: H.-P. Liermann (DESY-PETRA III, Germany) F. Langenhorst (U-Jena, Germany), T. Kenkmann (U-Freiburg, Germany)

E.-R. Carl, U. Mansfeld, H.-P. Liermann, A. Danilewsky, F. Langenhorst, L. Ehm, G. Trullenque, and T. Kenkmann. High-pressure phase transitions of α-quartz under nonhydrostatic dynamic conditions: A reconnaissance study at PETRA III. Meteoritics and Planetary Science, 52:1465-1474, 2017.

Phase transitions in Ferroic Materials

The community of material scientists is strongly committed to the research area of multiferroic materials, both for the understanding of the complex mechanisms supporting the multiferroism and for the fabrication of new compounds, potentially suitable for technological applications. The use of high pressure is a powerful tool in synthesizing new multiferroic, in particular magneto-electric phases, where the pressure stabilization of otherwise unstable perovskite-based structural distortions may lead to promising novel metastable compounds. The in situ investigation of the high-pressure behavior of multiferroic materials has provided insight into the complex interplay between magnetic and electronic properties and the coupling to structural instabilities.

Collaborators: J.B. Parise (SBU, USA), H. Liu (HPSTAR, China), E. Gilioli (CNR-IMEM ,Italy)

E. Gilioli and L. Ehm. High pressure and multiferroic materials: A happy marriage. IUCRJ, 1:590-603, 2014.

Structure and Properties of Nanocrystalline and Amorphous Materials

Mineralogy on the nanoscale is an emerging field in geological and environmental sciences. The recent advances in synchrotron high-energy total scattering techniques and the advancement in electron microscopy have shown that a large variety of Earth materials formerly believed to be amorphous are actually nanocrystalline with particle sizes of less than 10 nm. Nanominerals show profoundly different physical and chemical properties compared to their bulk counterparts due to the large surface area compared to the volume of the particle. These natural nanomaterials play an important role in, for example, acid mine drainage localities and in the effort to clean up contaminated ground water. However, the structure-property relationships in these nanominerals are practically unknown, leaving a large gap in our understanding of why some chemical or physical properties in nanominerals are depressed while others are enhanced. Recently, we made major breakthroughs in the determination of structure-property relationships in these complex nanominerals.

Collaborators: J.B Parise (SBU, USA) and B.L. Phillips (SBU, USA)

F. Marc Michel, Lars Ehm, Sytle M. Antao, Peter L. Lee, Peter J. Chupas, Gang Liu, Daniel R. Strongin, Martin A.A. Schoonen, Brian L. Phillips, John B. Parise . The structure of ferrihydrite. Science, 316:1726-1729 , 2007.

Formation and Stability of Clathrates

Clathrates (methane hydrates) are a global phenomenon, occurring in permafrost regions of the Arctic and in deep-water portions of most continental margins. A large amount off the greenhouse gas and energy source methane is stored in clathrates on the oceans sediments. Currently, clathrates deposits are investigated as a source of potentially carbon neutral form of energy. Injecting carbon-dioxide into the clathrate containing sediments will displace methane in the clathrate structure, which can be harvested, forming highly stable so-called carbon-dioxide hydrates. A key step for this hydrate technology to become feasible is to understand the real formation process of carbon-dioxide hydrates in sediment-hosted natural methane hydrates.

Besides their importance in the Earth's carbon cycle, clathrates play and important role in the structure and dynamics of planets and their icy satellites. Similar to the outer planets Jupiter, Saturn, Uranus, and Neptune; their moons lack a rocky crust. However, their surfaces are covered with ices that behave similarly to rocks. Furthermore, the behavior of ices and clathrates at pressure and temperature condition of the planetary interiors are currently not fully understood.

Collaborators: J.B Parise (SBU, USA) and T. Koga (SBU,USA)