Small-angle x-ray scattering of supercritical fluid Hg: Bi-impurity effect

Abstract

We have carried out small-angle x-ray scattering and x-ray transmission measurements of supercritical fluid Hg-0.2%Bi and pure Hg systems at SPirng-8 in Japan. We have obtained the static structure factors S(Q) in the low-momentum transfer region (0.5< Q <3 nm−1) for both samples at temperatures and pressures up to 1600 °C and 200 MPa. A Bi-impurity effect can be seen in both S(Q) and density deduced from x-ray transmission, only in the high temperature and high pressure region; the sign of the phase separation is seen near the critical density for Hg-0.2%Bi sample. We have analyzed S(Q) by Ornstein-Zernike formula and deduced the structure factors in the long-wavelength limit S(0), correlation lengths ξ, and corresponding short-range correlation lengths R = ξ≡/√S(0). Temperature variation of R is very similar to that of the density in each sample. This experimental fact hints that the variation of R is highly dependent on its metallic nature because the density is the most relevant parameter for the electronic features in fluid Hg and its impurity systems.