Ultrahigh pressure equation of state of tantalum to 310 GPa

ABSTRACT

The isothermal compression of transition metal tantalum (Ta) was studied in a diamond anvil cell by X-ray diffraction utilizing rhenium (Re) and gold (Au) as internal X-ray pressure standards. The Re pressure marker was employed during non-hydrostatic compression to pressures up to 310 GPa while the Au pressure marker was used during quasi-hydrostatic compression in a neon pressure-transmitting medium to 80 GPa. Two ultra-high pressure experiments were conducted on Ta and Re mixtures utilizing focused-ion beam machined toroidal diamond anvils with central flats varying from 8 microns to 16 microns in diameter. The Ta metal was observed to be stable in the body-centered-cubic phase to a volume compression V/V₀ = 0.581. The measured equations of state (EOS) of Ta using two different calibrations of the Re pressure marker are compared with the ambient temperature isotherm derived from shock compression data. We provide a detailed analysis of EOS fit parameters for Ta under quasi-hydrostatic and non-hydrostatic conditions.

KEYWORDS:

• Equation of state
• X-ray diffraction
• transition metals
• toroidal diamond anvils

Acknowledgements

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 No. DE-AC02-06CH11357. We also thank Dr. Richard Marten at the University of Alabama – Tuscaloosa for his assistance in the FIB machining of toroidal anvils, Sergey Tkachev of GSECARS for the neon gas-loading, and HPCAT 16-BM-D beamline support from Dmitry Popov and Changyong Park.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

We would like to acknowledge support from the U.S. National Science Foundation (NSF) under Metals and Metallic Nanostructures program grant number DMR-1608682. Los Alamos National Laboratory (LANL) is operated by Triad National Security, LLC for the DOE-NNSA under Contract No. 89233218CNA000001. NV, EKM, JSP, and BTS acknowledge funding support from LANL Science Programs 1 and 2.