Relaxation flow law of Fe2SiO4 olivine and spinel at high pressure: A stress and strain measurement using x-rays

Synchrotron x-rays have become an extremely compelling tool in studying material properties under high pressures. In addition to exploring means to reveal the information of material properties that is not obtainable before, developments using synchrotron x-rays have also enabled many reformations of traditional experiments. In this report, we present the results of stress and strain measurement at high pressures and temperatures using synchrotron x-ray diffraction and radiograph imaging techniques. For the first time, rheological properties of both the low pressure phase (olivine) and the high pressure phase (spinel) of Fe₂SiO₄ sample are derived from a single experiment. A clear strengthening in the material due to the phase transformation is observed. The stress and strain rate data measured at temperatures up to 1075K are used to derive the Periels plasticity flow law (ǎrepsilon'=ǎrepsilon'₀exp(-(Q)/(RT)(1-(σ )/(τ ))²)) for each phase, and yield an activation energy and Periels stress of 480+/-20 kJ/mol and 6.7+/-0.5 GPa for olivine phase and 460+/-20 kJ/mol and 6.5+/-0.5GPa for spinel phase. Compared with existing data for San Carlos olivine, a significant weakening by increasing iron content in the structure is revealed. Technical details and data processing for the experiment will be discussed.