Spinel oxides, with the general formula (AB₂O₄), are among the most abundant non-silicate minerals of the Earth’s crust and upper mantle. A special characteristic of spinels is their ability to host a wide range of cations.

Silicate minerals can also have spinel structure. In fact, ringwoodite (Mg,Fe)₂SiO₄ is one of the most abundant minerals of the Earth's transition zone (the region between 410 and 660 km depth).

In this project we conduct studies of the effects of cations substitution, degree of inversion and cations disorder in spinel oxides in a wide range of pressure conditions. The methods we use are Brillouin scattering, Raman scattering, synchrotron X-ray diffraction and first principles computations.

Fig.: The elastic moduli Cij of spinel-galaxite (MgAl2O4-MnAl2O4) as a function of Mg-Mn substitution

Silicate garnets (A₃B₂Si₃O₁₂) are a large family of silicates very well represented in the Earth’s crust, and they are among the major components of the upper mantle and transition zone rocks. Silicate garnets have been the subject of more than 30 studies dedicated to the determination of their full elastic tensor. However, due to the very rich range of chemical substitutions, our understanding of the systematic effect of chemical substitutions on the elastic tensor is far from being complete.

We conduct Brillouin scattering studies of series of natural and syntehtic silicate garnets single crystals selected to span almost ideal binary cations substitutions. In addition we investigate the effect of OH incorporation in natural spessartine (Mn₃Al₂Si₃O₁₂) and andradite (Ca₃Fe₂Si₃O₁₂).

Fig.: The elastic moduli Cij of a natural hydrospessartine (∼Mn₃Al₂(SiO₄)_2.5(H₄O₄)_0.5) compared with the anhydrous endmember (Mn₃Al₂Si₃O₁₂). The line is a model linear dependence based on the behavior of the system grossular (Ca₃Al₂Si₃O₁₂) – hibschite (Ca₃Al₂(SiO₄)_1.74(O₄H₄)_1.28).

The elastic properties of portlandite, which is an important compound of cement and a prototype of strongly anisotropic layered materials. We investigate stress-induced amorphization, the effects of experimental geometries and possible strategies to optimize the approach to analyze volume and axial strains for equation of state studies of anisotropic materials. We perform elasticity and equation of state measurements at high pressure in the diamond anvil cell and multi anvil apparatus measurement.

Fig.: The ambient temperature isothermal compression curve of portlandite (Ca(OH)₂) based on volume measurements in different compression devices (LVP: large volume press, DAC: diamond anvil cell). The colored symbols are our measurements, the curves our model compression curves based on the LVP and the DAC datasets. They are largely different due to the sensitivity of portlandite to non-hydrostatic stress in different compression devices.

Structural and elastic properties of silicate glasses with compositions of the most important components of the Earth mantle are investigated at the relevant deep Earth pressures. Sound velocity measurements are used to determine in situ high-pressure density.

Fig.: The pressure effect on the acoustic velocity of MgSiO₃ glass compressed to 25 GPa at ambient temperature. The plot shows anomalous change of pressure dependence at about 7 GPa and a large hysteresis in decompression. This is a typical indication of important changes in the compression behavior of this amorphous silicate.