Calibration of the diamond anvil Raman pressure gauge up to 420 GPa in a toroidal-DAC.

 

A modification of the Diamond Anvil Cell has recently been proposed to generate extreme static pressures so as to overpass the 400 GPa pressure limit of the conventional DAC. It is based on using a toroidal shape of the diamond culet [1]. In this toroidal-DAC (t-DAC), the stress state and the sample configuration are very similar to those seen in a conventional DAC. Good quality XRD and spectroscopic data can be measured. The recent synchrotron infrared measurements of the deuterium metal transition up to 470 GPa in a t-DAC illustrates the possibilities and the maturity of this device [2]. There is a growing use of the t-DAC worldwide to push the exploration of materials properties under multi-Mbar extreme pressures. Central for meaningful measurements is the correct pressure determination. There is thus a need to reliably calibrate a spectroscopic pressure gauge to replace the ruby scale above 150 GPa up to at least 500 GPa.

The high-frequency step of the T2g Raman spectra of the stressed diamond anvil is currently used. This spectroscopic pressure gauge was calibrated by Akahama et al, first up to 300 GPa, as scale 1, and then extended to 400 GPa, as scale 2 [3]. However, scale 2 is suspected to largely overestimate the pressure above 400 GPa because it is based on a Platinum EOS that is less compressible than most recent determinations. For the present calibration, we have used the XRD measured volumes both of gold and of rhenium [4,5]. This was achieved by compressing pure gold embedded in a rhenium gasket. XRD using a sub-micron beam enables to map the pressure distribution within a 5 μm diameter sample and probe the rhenium pressure at the interface with the gold sample. Data have been collected up to 420 GPa so far.

In this communication, we will detail the experimental protocol used, show the data we obtained and propose a new pressure scale based on the Raman spectrum of the stressed diamond anvil and discuss its validity range.

 

[1] A. Dewaele et al. Nature Communication 9, 2913 (2018). [2] P. Loubeyre et al. Phys. Rev. Lett. 129, 035501 (2022). [3] Y Akahama et al,. J. Phys. Conf. Ser. 215, 012195 (2010). [4] S. Anzelini et al, J. Appl. Phys. 115, 043511 (2014). [5] D. Fratanduono et al. Science 372, 1063 (2021).