Thermal equation of state of cubic silicon carbide at high pressures

The thermoelastic properties of SiC with a zinc-blende crystal structure are experimentally determined. Previous experimental studies contained errors due to significant uncertainties of measured pressures and temperatures and unreleased residual stresses. The determined thermal expansion coefficient at high pressures is 1.5 times higher than previously found.

Abstract

We have performed in situ X-ray diffraction measurements of cubic silicon carbide (SiC) with a zinc-blende crystal structure (B3) at high pressures and temperatures using multi-anvil apparatus. The ambient volume inferred from the compression curves is smaller than that of the starting material. Using the 3^rd-order Birch-Murnaghan equation of state and the Mie-Grüneisen-Debye model, we have determined the thermoelastic parameters of the B3-SiC to be 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 Grüneisen parameter, respectively. Using the 3^rd-order Birch-Murnaghan EOS with the thermal expansion coefficient, the thermoelastic parameters have been found as K ₀=221±3 GPa, K ₀’,=5.2±0.4, α ₀=0.90±0.02 ⋅ 10⁻⁵ ⋅ K⁻¹, where α₀ is the thermal expansion coefficient at room pressure and temperature. We have determined that paired B3-SiC – MgO calibrants can be used to estimate pressure and temperature simultaneously in ultrahigh-pressure experiments up to 60 GPa.

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