[S-IT14] Deep Earth Sciences

[SIT14-07] A step toward consistent pressure measurements in multi-anvil and diamond cells: Simultaneous compression of ruby, NaCl, and Au

*Yanbin Wang¹, Guoyin Shen², Jesse S. Smith² (1.Center for Advanced Radiation Sources, University of Chicago, 2.HPCAT, X-Ray Science Division, Argonne National Laboratory)

Keywords:Consistent pressure scales, Equation of state, Synchrotron x-ray diffraction, multi-anvil press, diamond-anvil cell, Ruby2020 scale

NaCl and Au are two commonly used pressure standards and many researchers have reported various equations of state (EoSs). Inter-consistency among these diffraction-based EoSs has not been systematically investigated. Recently, a new ruby pressure scale has been proposed which is consistent with shock-wave data on metals, and elasticity and EoS data on ionic, covalent, and metallic materials up to 150 GPa [1]. In this study, we compress NaCl and Au in a membrane-driven diamond-anvil cell (DAC) [2] in helium (He) pressure medium, along with simultaneous ruby fluorescence measurements. Monochromatic radiation with wavelength of 0.4246 A was used for x-ray diffraction, with a beam size of ~5 um, which covered both NaCl and Au in the DAC. An online ruby system, with its optical path reflected by an x-ray transparent carbon mirror, was used to measure ruby pressure simultaneously while x-ray diffraction is collected. Pressure was increased/decreased by a pair of membrane pressure controllers continuously, reaching 20 GPa in 2 hours. Data collection of ruby fluorescence and x-ray diffraction were automated and synched at 1 sec intervals. In one experiment, 7200 and 1000 measurements were conducted upon compression and decompression, respectively. Unit-cell volumes of NaCl and Au were extracted using Dioptas [3] and Multifit [4] and fitted based on the Ruby2020 pressure scale [1] to the Rydberg-Vinet (RV) [5] and third-order Birch-Murnaghan (BM3) [6] EoSs. The highly redundant measurements reveal subtle differences in materials’ responses to compression and decompression. Solidification of the He medium has a clear effect on the unit cells above ~14 GPa. Thus, only the compression data below He solidification pressure were used to fit equations of state for NaCl and Au. Fixing the ambient isothermal bulk moduli according to previous ultrasonic measurements [7, 8], we obtained EoSs for NaCl and Au that are consistent with Ruby2020 to within +/-0.05 GPa. These results demonstrate the potential of establishing mutually consistent pressure scales for both diffraction-based and fluorescence-based pressure scales, which may be applied to both multi-anvil devices and the DAC.
References cited:
[1] Shen et al., HPR, 2020 (10.1080/08957959.2020.1791107); [2] Sinogeikin et al., RSI, 2015 (10.1063/1.4926892); [3] Prescher & Prakapenka, HPR, 2015 (10.1080/08957959.2015.1059835); [4] Merkel & Hilairet, JAC, 2015 (10.1107/S1600576715010390); [5] Vinet et al., J. Phys. C, 1986 (10.1088/0022-3719/19/20/001); [6] Birch, JGR, 1986 (10.1029/JB091iB05p04949); [7] Matsui et al., Am Min, 2012 (10.2138/am.2012.4136); [8] Anderson et al., JAP, 1989 (10.1063/1.342969).