Dr. Sergey M. NIKITIN

Knowledge of pressure-dependences of sound velocities and elastic moduli of liquids and solids at Megabar pressures and evolution of texture of polycrystalline solids on compression is of extreme importance for a few branches of natural sciences such as condensed matter physics, physics of the Earth and planetology, as well as for monitoring and predicting of earthquakes and tsunamis or nuclear weapons test control.

 

This research work is devoted to the use of laser ultrasound in high-pressure physics. The research is done using the recently established technique of laser ultrasonic measurements in a diamond anvil cell which allows investigation of the sound propagation and determination of the acoustic wave velocities at ultrahigh pressures. Time domain Brillouin scattering was applied here to depth-profiling of polycrystalline aggregate of ice compressed in a diamond anvil cell to Megabar pressures. The technique allowed examination of characteristic dimensions of elastic inhomogeneities and texturing of polycrystalline ice in the direction, normal to the diamond anvil surfaces with sub-micrometer spatial resolution via time-resolved measurements of variations in the propagation velocity of the acoustic pulse travelling in the compressed sample. It was applied to measure the acoustic velocities in H2O ice up to 84 GPa. The developed imaging technique provides for each crystallite (or a group of crystallites) in chemically homogeneous transparent aggregate, usable information on its orientation as well as on the value of the elastic modulus along the direction of the sound propagation. This extends the basis for a successful application of highly developed micromechanical models of solids deformation at Mbar pressure. On long term, such experiments extended to Earth’s minerals and high or low temperatures would insure a significant progress in understanding of convection of the Earth’s mantle and thus evolution of this and other planets.