Experimental and theoretical P-V-T equation of state for Os₂B₃

ABSTRACT

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 the 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 $\alpha ={\alpha }_0+{\alpha }_{1}T-{\alpha }_2{T}^{-2}$, the thermal expansion coefficients were determined to be ${\alpha }_0=1.862\times {10}^{-5}$ K⁻¹, ${\alpha }_1=0.841\times {10}^{-9}$ K⁻², and ${\alpha }_2=-0.525$ K. Density functional theory (DFT) with the quasi-harmonic approximation (QHA) were 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.

KEYWORDS:

• Metal borides
• thermal equation of state
• high pressure high temperature
• synchrotron x-ray diffraction

Acknowledgments

This research is funded by the U.S. National Science Foundation (NSF) under Metals and Metallic Nanostructures program grant number DMR-1904164. Portions of this work were performed at HPCAT (Sector 16), Advanced Photon Source (APS), Argonne National Laboratory. HPCAT operations are supported by DOE-NNSA’s Office of Experimental Sciences. We would like to acknowledge experimental support from the HPCAT beamline scientist Dr. Ross Hrubiak. The Advanced Photon Source is a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. The calculations were performed on the Frontera computing system at the Texas Advanced Computing Center. Frontera is made possible by NSF award OAC-1818253.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This research is funded by the National Science Foundation (NSF) under Metals and Metallic Nanostructures program [grant number DMR-1904164]. Portions of this work were performed at HPCAT (Sector 16), Advanced Photon Source (APS), Argonne National Laboratory. HPCAT operations are supported by DOE-NNSA’s Office of Experimental Sciences. The Advanced Photon Source is a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under [contract number DE-AC02-06CH11357]. The calculations were performed on the Frontera computing system at the Texas Advanced Computing Center. Frontera is made possible by NSF award [OAC-1818253].