Thermoelastic Equation of State of Boron Suboxide B6O up to 6 GPa and 2700 K: Simplified Anderson Grüneisen Model and Thermodynamic Consistency1
Résumé
The p V T equation of state of superhard boron suboxide B6O has been measured up to 6 GPa and 2700 K using multianvil technique and synchrotron X ray diffraction. To fit the experimental data, the theoretical p V T equation of state has been derived in approximation of the constant value of the Anderson Grüneisen parameter δT . Bulk modulus B0 =181 GPa and its first pressure derivative B0′ = 6 at 300 K;two parameters describing thermal expansion at 0.1 MPa, i.e., a = 1.4 × 10-5 K-1 and b = 5 × 10-9 K-2as well as δT = 6 have been included in the model. The good agreement between fitted and experimental isobars has been achieved to the absolute volume changes up to 5% as compared to the volume at standard conditions, V0. The fitted thermal expansion at 0.1 MPa well consistent with the experimental data as well as with ambient pressure heat capacity cp, bulk modulus B0 and δT describing its evolution with volume and temperature have been discussed. The fitted value of Grüneisen parameter γ = 0.85 in agreement with previous empiric estimations for B6O and experimental values for other boron rich solids has been reported