- Physics Program Director / Physics Faculty at the Department
of Physical Sciences at Phoenix College
PHY111, PHY112, PHY121, PHY131
My research interests concentrate on the study of physical and chemical properties of Earth and other planetary interiors minerals. I study the plastic deformation and phase transitions of materials at high pressure and temperature using the laser-heated diamond-anvil cell combined with synchrotron X-ray diffraction.
The Earth mantle and inner core are submitted to large scale movements of solid materials. The physical process allowing the flow of solid materials is connected to plastic properties and, in particular, dislocations. It is the source of seismic wave velocities anisotropy. However, the deformation mechanisms of deep Earth minerals are poorly understood. The study of the plastic properties of these minerals is therefore critical for understanding deformation and dynamical behavior within the earth.
Deep in the Earth’s interior, minerals are under extreme conditions; the temperature reaches several thousand degrees and the pressure is more than one million times the atmospheric pressure. The experimental study of the plasticity of those minerals requires deformation experiments under high pressure and temperature.
During my master’s degree in materials sciences, my research project was focused on the study of textures and phase transformation in iron. I have investigated the effect of pressure on iron in-situ by means of high pressure radial X-ray diffraction technique using a diamond anvil cell. In this project, I concentrated on the study of Lattice Preferred Orientations (LPO) before, during and after the α→ε→α transition and their relation to plastic properties of those phases.
The analysis of LPO and lattice strains can be used to obtain information about active deformation mechanisms. They are important for the understanding of the earth inner core seismic anisotropy as it is supposed originate from preferred orientations of iron crystals resulting of plastic deformation.
It is usually assumed that textures (LPO) result from deformation through the movement of dislocations along slip systems. Usually, Transmission Electron Microscopy technique (TEM) is used to identify dislocations directly. For high pressure phases which can not be quenched at ambient pressure, TEM can not be used. For this reason, in-situ experimental deformation mechanisms studies on these high pressure phases are usually limited to textures analysis, at the polycrystalline scale, from which slip systems are inferred.
During my PhD, I developed a completely new technique to investigate dislocations directly in materials using X-ray diffraction. I used in-situ 3D X-Ray diffraction (3D-XRD) on polycrystalline sample of MgGeO3 post-perovskite at 90 GPa. Using this technique, I extracted and studied individual grains within the polycrystalline diffraction images, including their individual orientations, positions, and strain tensors. I then used X-Ray Line Profile Analysis (XLPA) on high resolution diffraction images of these grains to characterize dislocations in terms of character and dislocation density from the anisotropic broadening of the diffraction peaks.
Based on the prevailing dislocations in MgGeO3 post-perovskite obtained, and assuming that they apply to silicate post-perovskite under deep mantle conditions, I then investigated the elastic anisotropy of a pPv polycrystal and modeled the shear wave splitting for a comparison with the observations of seismic anisotropy in most of D”.
The experimental development and its application to the post-perovskite for a direct, in-situ investigation of dislocations are of great importance to circumvent the challenges of deducing plastic properties of pPv from textures measurements, and from numerical modeling. The results are also significant for understanding deformation processes in post-perovskite and D” and in particular the origin of the seismic anisotropy.
The combination of techniques developed, 3D-XRD and XLPA, is a very powerful tool for the study of microscopic defects, in-situ, at high pressure. It can now be applied to other high pressure materials that can not be quenched to ambient pressure.
- In Situ high pressure and temperature synchrotron X-ray diffraction experiments using diamond anvil cells.
- Phase transitions, equations of sate and plastic properties at high pressure-temperature of wide range of mineralogical compositions of the interior of the earth and other planets.
- Effect of water on the compressional behavior of Earth minerals.
- 3D X-ray diffraction to extract single grains within a polycrystalline sample.
- Stress, strain and textures analysis from X-ray diffraction images.
- Study of dislocations using the X-ray Line Profile Analysis.
Last achieved projects
- Phase transitions and properties at high pressure-temperature of wide range of mineralogical compositions:
– Water in dense pure silica polymorphs.
– Effect of water on the compressional behavior of SiO2 stishovite.
– Phase transition and physical properties of SiC in the deep interiors of carbide exoplanets.
Research group I have worked with at ASU
Geophysics group, within the School of Earth and Space Exploration. They are a multi-disciplinary team of scientists combining the fields of geodynamics, mineral physics, and seismology. More information are available in the geophysics website.
Mineral physics group led by Dan Shim. The lab hosts instruments and high pressure and temperature devices for studying the properties, chemical reactions, phase transitions, and atomic-scale structures of Earth and planetary materials at the pressure and temperature conditions of Earth and planetary interiors. For more information visit Dan Shim group website.