Complexity in the medium-range order of gallium as a polyvalent liquid metal

Abstract

Simplicity in chemical composition does not always translate into simplicity in the structures and dynamics of liquids and solids. Some elementary liquid metals, such as gallium, show unusual behaviors in thermodynamic and transport properties as a result of their complex atomic structure and dynamics. In this work, we study the real-space atomic correlation function of liquid gallium by neutron scattering. In the pair-distribution function, there exist two kinds of medium-range order (MRO), characterized by oscillations beyond the first nearest neighbors. On the other hand, the first neighbor shell shows only one kind of bond. The two types of MRO are strongly overlapping in space and fluctuating in time. We propose that they are the basis for anomalous behavior of liquid gallium. This view challenges the current view that liquid gallium consists of fluctuating metallic and insulating domains. These findings shed new light on the interpretation of similar microscopic anomalies observed in other semi-metallic liquids.

Figures (3)

• Figure 1: (a) The measured structure factor, $S(Q)$ at 310 K (solid line), two superimposed Lorentzian fit to the first peak of $S(Q)$ (dashed line), and the decomposed Lorentzian functions describing the main peak and the shoulder (dotted-dashed line). (b) The measured pair distribution function, $r(g(r)-1)$ (solid line) and the Fourier transformation of the fit to the first peak of $S(Q)$ (dashed line). Inset: Zoom-in view of the first peak in $g(r)$.
• Figure 2: (a) The measured pair distribution function, $r(g(r)-1)$ (dotted line) and the best fit of the higher-order peaks ($r > 3.8 \mathrm{\AA}$) using Eq. (\ref{['eq:MRO']}) with one (dashed line) and two (solid line) sinusoidal components at 390 K. (b) The full set of the measured $r(g(r)-1)$ with the best fit using Eq. (\ref{['eq:MRO']}) between 310 K (bottom) and 950 K (top). The values on the y-axis correspond to the curve at 310 K; the remaining solid curves are displaced upwards with a step of 2. The full set of temperatures is: 310, 350, 390, 430, 470, 510, 550, 650, 750, 850, and 950 K.
• Figure 3: The temperature dependence of inverse coherent length, $\xi_s^{-1}$. $\xi_s(T)$ follows a Curie-Weiss law with $T_{\mathrm{IG}} = -498~\mathrm{K}$.).