17:15 〜 18:45
[SMP23-P08] Thermal equation of state of B3 SiC at high pressures
Silicon carbide SiC is a solid hard compound stable at ambient conditions. Its natural form is named moissanite. Moissanite has been found in various rocks such as eclogites, serpentinites, and chromitites. Moreover, it was found as inclusions in diamonds from kimberlites. SiC minerals could be dominant in the deep interiors of carbon-rich extrasolar terrestrial planets [1]. High-pressure investigation of SiC is therefore vital for Earth and planetary sciences.
SiC has a huge number of polytypes. The most studied one is beta silicon carbide (β-SiC), with a zinc blende crystal structure (B3). This SiC transforms to its high-pressure modification with a rock-salt structure (B1) between 60 and 80 GPa at room temperature. The pressure-volume equation of state (EOS) of the B3 SiC was investigated by Raman and Brillouin spectroscopies, as well as by in situ X-ray diffraction (XRD). XRD studies also determined the thermal EOS of the B3 SiC. These results were used to model the mass-radius relations and to determine rheological parameters for ideal C-rich exoplanets using numerical simulations [2]. However, since all these studies were conducted using laser-heated diamond-anvil cells, the pressures and temperatures had significant uncertainties, leading to an incorrect EOS and also incorrect exoplanet models. Thus, the thermal EOS of the B3 SiC should be reinvestigated using experimental techniques with more precise pressure and temperature determination.
We determined EOS of B3 SiC using in situ X-ray diffraction (XRD) with a 3x5-MN six-axis multi-anvil apparatus, Aster-15, installed at beamline P61B at the German synchrotron radiation facility, DESY. Using 3rd-order Birch-Murnaghan (3BM) and Mie-Gruneisen-Debye (MGD) models, we determined the bulk modulus and thermal pressure parameters of B3 SiC as K0 = 228(3) GPa, K0', = 4.4(0.4), q = 0.27(0.37), where K0, K0' and q are the isothermal bulk modulus, its pressure derivative and logarithmic volume dependence of the Gruneisen parameter, respectively. Using the 3BM EOS with thermal expansion, the thermoelastic parameters were found as K0 = 221(3) GPa, K0', = 5.2(0.4), a0 = 0.90(0.02) x 10-5 x K-1, where a0 is the thermal expansion coefficient at room pressure and temperature. The obtained elastic parameters are comparable with those determined in previous studies, whereas the thermal pressure parameters are different. Our results allow us to propose a new model of the mass-radius relation of ideal C-rich exoplanets.
Figure caption
Figure 1: Mass-radius relations for different idealized exoplanet interiors together with the standard comparison curves (pure Fe, MgSiO3 and Earth-like). The black dots show the measured masses and radii for Earth and Venus. The figure is redrawn from Ref [2].
[1] J. C. Bond, D. P. O'Brien and D. S. Lauretta, The Astrophysical Journal, 2010, 715, 1050.
[2] F. Miozzi, G. Morard, D. Antonangeli, A. N. Clark, M. Mezouar, C. Dorn, A. Rozel and G. Fiquet, Journal of Geophysical Research: Planets, 2018, 123, 2295-2309.
SiC has a huge number of polytypes. The most studied one is beta silicon carbide (β-SiC), with a zinc blende crystal structure (B3). This SiC transforms to its high-pressure modification with a rock-salt structure (B1) between 60 and 80 GPa at room temperature. The pressure-volume equation of state (EOS) of the B3 SiC was investigated by Raman and Brillouin spectroscopies, as well as by in situ X-ray diffraction (XRD). XRD studies also determined the thermal EOS of the B3 SiC. These results were used to model the mass-radius relations and to determine rheological parameters for ideal C-rich exoplanets using numerical simulations [2]. However, since all these studies were conducted using laser-heated diamond-anvil cells, the pressures and temperatures had significant uncertainties, leading to an incorrect EOS and also incorrect exoplanet models. Thus, the thermal EOS of the B3 SiC should be reinvestigated using experimental techniques with more precise pressure and temperature determination.
We determined EOS of B3 SiC using in situ X-ray diffraction (XRD) with a 3x5-MN six-axis multi-anvil apparatus, Aster-15, installed at beamline P61B at the German synchrotron radiation facility, DESY. Using 3rd-order Birch-Murnaghan (3BM) and Mie-Gruneisen-Debye (MGD) models, we determined the bulk modulus and thermal pressure parameters of B3 SiC as K0 = 228(3) GPa, K0', = 4.4(0.4), q = 0.27(0.37), where K0, K0' and q are the isothermal bulk modulus, its pressure derivative and logarithmic volume dependence of the Gruneisen parameter, respectively. Using the 3BM EOS with thermal expansion, the thermoelastic parameters were found as K0 = 221(3) GPa, K0', = 5.2(0.4), a0 = 0.90(0.02) x 10-5 x K-1, where a0 is the thermal expansion coefficient at room pressure and temperature. The obtained elastic parameters are comparable with those determined in previous studies, whereas the thermal pressure parameters are different. Our results allow us to propose a new model of the mass-radius relation of ideal C-rich exoplanets.
Figure caption
Figure 1: Mass-radius relations for different idealized exoplanet interiors together with the standard comparison curves (pure Fe, MgSiO3 and Earth-like). The black dots show the measured masses and radii for Earth and Venus. The figure is redrawn from Ref [2].
[1] J. C. Bond, D. P. O'Brien and D. S. Lauretta, The Astrophysical Journal, 2010, 715, 1050.
[2] F. Miozzi, G. Morard, D. Antonangeli, A. N. Clark, M. Mezouar, C. Dorn, A. Rozel and G. Fiquet, Journal of Geophysical Research: Planets, 2018, 123, 2295-2309.