Abstract
The compression of argon is measured between 10 K and 296 K up to 20 GPa and and up to 114 GPa at 296 K in diamond anvil cells. Three samples conditioning are used: (1) single crystal sample directly compressed between the anvils, (2) powder sample directly compressed between the anvils, (3) single crystal sample compressed in a pressure medium. A partial transformation of the face-centered cubic (fcc) phase to a hexagonal close-packed (hcp) structure is observed above 4.2–13 GPa. Hcp phase forms through stacking faults in fcc-Ar and its amount depends on pressurizing conditions and starting fcc-Ar microstructure. The quasi-hydrostatic equation of state of the fcc phase is well described by a quasi-harmonic Mie–Grüneisen–Debye formalism, with the following 0 K parameters for Rydberg-Vinet equation: V_0 = 38.0 Å^3/at, K_0 = 2.65 GPa, K'_0 = 7.423. Under the current experimental conditions, non-hydrostaticity affects measured P–V points mostly at moderate pressure (le 20 GPa).
Highlights
The compression of argon is measured between 10 K and 296 K up to 20 GPa and and up to 114 GPa at 296 K in diamond anvil cells
The prediction of the structure adopted by rare gas solids is more difficult to address, because face-centered cubic and hexagonal close packed rare gas solids are almost isoenergetic, so that subtle effects such as many-body interactions, or phonon dispersion curves play a role in their relative stability[7,8,9]
Rare gases crystallize from the liquid under fcc structure, and it has been observed that compression favors the hcp phase in the case of xenon/krypton, with a sluggish transition observed or expected around 80 GPa/400 GPa at 300 K 10–12
Summary
The compression of argon is measured between 10 K and 296 K up to 20 GPa and and up to 114 GPa at 296 K in diamond anvil cells. Rare gases crystallize from the liquid under fcc structure, and it has been observed that compression favors the hcp phase in the case of xenon/krypton, with a sluggish transition observed or expected around 80 GPa/400 GPa at 300 K 10–12. Fcc argon crystallizes at 1.4 G Pa13, and shows evidence of nonhydrostatic behavior at pressures as low as 2 GPa14 It becomes even stronger above 30 GPa, with pressure gradients of more than 1 GPa/10 μm[14,15]; this might have biased equation of state data measured by compressing argon samples, which completely fills the high pressure chamber of diamond anvil cells[14,16,17,18,19,20]. We used pure argon and grew argon crystals embedded in an ArNe2 laves phase matrix, which acts as a soft pressure transmitting medium around it21, enabling an accurate
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