Photon Factory Activity Report 2022 #40 (2023)

AR-NE1A/2019G003/2021G019

Compressibility of Ar
1

Shigeaki ONO1,*Research Institute for Marine Geodynamics, Japan Agency for Marine-Earth Science andTechnology (JAMSTEC), Yokosuka 237-0061, Japan

1 Introduction
Rhenium (Re) is a group VII transition metal thatcrystallizes in a hexagonal close-packed (hcp) structure.
The high-pressure behaviors of Re have been studied
widely, as Re has a high bulk modulus value (~350 GPa)
compared with other metals. It is known that Re has thesecond-highest bulk modulus value after Os. Since Re isused as gasket material in diamond anvil cell experiments,
there is considerable interest in its high-pressure behavior.
The equation of state (EOS) for Re has often been used asa pressure marker at extremely high pressures. An
investigation of EOS could therefore improve thereliability of high-pressure experimental studies. Therefore,
we performed high-pressure experiments to determine theroom temperature EOS for Re.
2 Experiment
The high-pressure and high-temperature X-ray
diffraction experiments were performed using a diamondanvil cell (DAC) high-pressure apparatus with a laserannealing system. The culet size of the diamond anvil was
300 or 150 µm, and Re reagent powder (99.9% purity) wasused as the starting material. Powdered sample was
sandwiched between pellets of NaCl powder, which wasused as the pressure-transmitting medium and the pressurereference. After annealing, we performed in situ
measurements using the synchrotron X-rays 5–10 min. The
sample was probed using angle-dispersive X-ray
diffraction, employing the AR-NE1A synchrotron
beamline at KEK, Japan. The angle-dispersive X-ray
diffraction patterns were obtained on an image platesystem (Rigaku R-AXIS, Japan).
3 Results and Discussion
Typical diffraction data are shown in Fig. 1. Aftercompression to the desired pressure, stress broadening ofeach diffraction peak was observed, which decreased
drastically after laser annealing. This indicates that thedifferential stress under compression was released onannealing. Diffraction data after annealing were used todetermine the EOS, since the differential stress oftencauses bias in the relationship between volume andpressure. The room-temperature bulk modulus of Re wasmeasured in the pressure range 0 to 115 GPa using a laserannealing diamond anvil cell and the synchrotron X-ray
diffraction method. A Vinet equation of state fitted to the300 K data yielded a bulk modulus of KT0 = 384 GPa anda pressure derivative of K’T0 = 3.26 [1]. The value of thebulk modulus obtained in our experiments differs slightly
from those reported from previous experiments without

annealing, KT0 = 330~360 GPa. The difference between
our experimental method and the approaches used inprevious studies is related to the use of annealing before
the acquisition of X-ray diffraction data. It is known thatdifferential stress accumulates in the sample chamber
during room-temperature compression, and this stressoften has an influence on the measurement of the elastic
properties of solids. In our study, laser-heated annealing
was performed to minimize the influence of the differential
stress at each pressure increment. The differences between
our value and those reported in previous studies are
therefore likely to be due to the differential stress in thesample chamber..

Fig. 1: Labels for the diffraction peaks are as follows: R –Re with hexagonal structure; S – B1-type NaCl. Numberson the labels correspond to the indices of hexagonal or
cubic symmetry. Monochromatic incident X-ray beam
wavelength: λ = 0.4110 Å.
Acknowledgement
We thank the PF staffs for their helps in carrying out theexperiments.
References[1] S. Ono, Equation of state determination for rhenium
using first-principles molecular dynamics calculations
and high-pressure experiments, Adv. Condens. Matter
Phys., 2022, 7545777, doi.org/10.1155/2022/7545777* sono@jamstec.go.jp