Internally consistent elasticity measurements of mantle minerals at high-pressure and high-temperature by Brillouin spectroscopy and X-ray diffraction

Abstract:

Elasticity is a material property that reflects the atomic structure and interatomic forces in crystalline materials. As a result, elastic properties are strongly affected by changes in pressure and temperature. In Earth Sciences, knowledge of the elastic behavior of geomaterials at pressure and temperature conditions of the Earth’s interior is key to constrain our planet’s inner structure and dynamics through forward modelling of seismic observables. Here, we will discuss internally consistent single-crystal elasticity measurements that combine the opportunities emerging from the recent development of combined Brillouin scattering (to derive acoustic wave velocities) and x-ray diffraction (XRD) systems (for structure and unit-cell parameter determination) with the advantages of sophisticated sample preparation using the focused ion beam (FIB) technique [1]. We will show results of experiments on mantle minerals that were performed using the combined Brillouin scattering and rotating anode XRD system at the Bayerisches Geoinstitut BGI. Multiple single-crystals, FIB-tailored in size and shape, were loaded in the single sample chambers of resistively-heated diamond-anvil cells (DAC). Such a multi-sample approach allows for internally consistent determinations of all independent elastic constants from low-symmetry crystals by Brillouin spectroscopy and x-ray diffraction measurements. Furthermore, the multi-sample approach facilitates direct quantification of the effects of chemical substitution on the structure and elasticity of high-symmetry crystals at non-ambient conditions. Our experimental approach eliminates uncertainties arising from the combination of data collected under (potentially) different conditions in several DAC runs, in different laboratories and/or from using different pressure-temperature sensors. We will also discuss the possibility to derive pressure independent from a secondary pressure scale.

[1] H. Marquardt, K. Marquardt, Am. Mineral. 97, 299-304 (2012).