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

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 (Formula presented.), the thermal expansion coefficients were determined to be (Formula presented.) K⁻¹, (Formula presented.) K⁻², and (Formula presented.) 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.