EXTREME CONDITIONS: COMBINING ENERGETIC ION BEAMS WITH HIGH-PRESSURE CELLS

During the past few years, there has been an upsurge of interest in the response of materials to extreme conditions, particularly combinations of pressure, temperature and high-energy irradiation. With a recently developed approach, this regime may now be explored. Energetic ions can be accelerated and used to deposit exceptional amounts of kinetic energy (GeV) within an exceedingly short interaction time (less than fs) into nanometer-sized volumes, resulting in extremely high energy densities (up to tens of eV/atom). Further, the high-energy ion beams can be combined with high-pressure techniques by injecting relativistic ions from one of the world’s largest accelerator facilities (GSI – Helmholtz Center for Heavy Ion Research – Darmstadt, Germany) through the mm-thick diamond anvil of a high-pressure cell into a target under pressure. The damage zones form tracks that are 5 to 10 nm in diameter. The damage accumulates as tracks overlap with increasing fluence. This approach allows for the investigation of the behavior of materials under very extreme conditions and opens up unprecedented possibilities for the synthesis of new materials.

We have investigated a number of oxide, silicate and phosphate structures at high pressures during irradiation experiments. Radiation-induced energy deposition into highly compressed materials (several tens of GPa) can dramatically modify phase-transformation pathways. The combined use of advanced in situ (synchrotron X-ray diffraction and Raman spectroscopy) and ex situ (transmission electron microscopy) characterization techniques in experiments up to 65 GPa have revealed: (i) the stabilization of a new metastable high-pressure phase Gd₂Zr₂O₇ pyrochlore and (ii) the transformation into high-pressure and high-temperature phases of ceria (CeO₂), zirconia (ZrO₂) at unexpectedly low pressures and radiation fluences. Ion beam irradiation can also be used to simulate and investigate the formation and annealing of fission tracks in minerals, such as zircon and apatite.