Thermoelastic behavior of transition metal boride Os2B3 was studied under quasi-hydrostatic and isothermal conditions in a Paris-Edinburgh cell to 5.4 GPa and 1273 K. In-situ Energy Dispersive X-ray diffraction was used to determine interplanar spacings of the hexagonal crystal structure and thus the volume and axial compression. P-V-T data were fitted to a 3rd Order Birch-Murnaghan equation of state with a temperature modification to determine thermal elastic constants. The bulk modulus was shown to be K0 = 402 ± 21 GPa when the first pressure derivative was held to K0’ = 4.0 from the room temperature P-V curve. Under a quadratic fit α=α_0+α_1 T-α_2 T^(-2), the thermal expansion coefficients were determined to be α_0=1.862×10^(-5) K-1, α_1=0.841×10^(-9) K-2, and α_2=-0.525 K. Density functional theory (DFT) with the quasi-harmonic approximation (QHA) were further employed to study Os2B3, including its P-V-T curves, phonon spectra, bulk modulus, specific heat, thermal expansion, and the Grüneisen parameter. A good agreement between the first-principle theory and experimental observations was achieved, highlighting the success of the Armiento-Mattsson 2005 generalized gradient approximation functional employed in this study and QHA for describing thermodynamic properties of Os2B3.
Thermal Pressure in the Thermal Equation of State for Solid and a Proposed Substitute
The thermal equation of state (TEOS) for solids is a mathematic model among pressure, temperature and density, and is essential for geophysical, geochemical, and other high pressure–temperature (high P–T) researches. However, in the last few decades, there has been a growing concern about the accuracy of the pressure scales of the calibrants, and efforts have been made to improve it by either introducing a reference standard or building new thermal pressure models. The existing thermal equation of state,
- Publication Date:
- NSF-PAR ID:
- 10372512
- Journal Name:
- International Journal of Thermophysics
- Volume:
- 43
- Issue:
- 11
- ISSN:
- 0195-928X
- Publisher:
- Springer Science + Business Media
- Sponsoring Org:
- National Science Foundation
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