Crystal structure, temperature, and strength of Ta ramp compressed to Megabar pressures

We conducted experiments to investigate the crystal structure, temperature, and strength of tantalum under ramp compression using laser pulse shaping at the National Ignition Facility (NIF) and the Dynamic Compression Sector (DCS). At NIF, nanosecond x-ray flashes from a laser-heated foil probed the sample, while at DCS, 100 ps x-ray pulses from the Advanced Photon Source were used. Pressure histories were determined via velocimetry in all experiments.



X-ray diffraction measurements taken at the NIF confirm that tantalum retains its body-centered-cubic (BCC) structure and is inconsistent with the proposed Pnma structure at pressures up to ~500 GPa. EXAFS measurements, also recorded at the NIf, of the tantalum L3 edge further confirm the BCC structure, while also providing temperature data consistent with predictions from radiation hydrodynamics simulations when including plastic work heating. Preliminary x-ray diffraction measurements at DCS, conducted in ramp compressed tantalum up to ~100 GPa, complements these findings by measuring strength-induced deviatoric strain. We compare the temperatures determined from EXAFS measurements and our deviatoric strain measurements to various high-pressure strength models for tantalum^1,2.

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