Experimental and ab initio molecular dynamics simulation studies of liquid ${\text{Al}}_{60}{\text{Cu}}_{40}$ alloy

X-ray diffraction and ab initio molecular dynamics simulation studies of molten ${\text{Al}}_{60}{\text{Cu}}_{40}$ have been carried out between 973 and 1323 K. The structures obtained from our simulated atomic models are fully consistent with the experimental results. The local structures of the models analyzed using Honeycutt-Andersen and Voronoi tessellation methods clearly demonstrate that as the temperatures of the liquid is lowered it becomes more ordered. While no one cluster-type dominates the local structure of this liquid, the most prevalent polyhedra in the liquid structure can be described as distorted icosahedra. No obvious correlations between the clusters observed in the liquid and known stable crystalline phases in this system were observed.

Figure 1

(Color online) Experimental total structure factor $S\left(q\right)$ of the liquid ${\text{Al}}_{60}{\text{Cu}}_{40}$ alloy at different temperatures. Inset shows the details of the second diffuse scattering peak.

Figure 2

(Color online) The total and partial pair-correlation functions $g\left(r\right)$ of the liquid ${\text{Al}}_{60}{\text{Cu}}_{40}$ alloy at different temperature. The experimental data transformed to the PCF using Eq. (1) are shown as lines in (a), the partial pair-correlation functions $g\left(r\right)$ of the liquid ${\text{Al}}_{60}{\text{Cu}}_{40}$ alloy at four different temperatures using two different supercells are shown in (b), (c), and (d).

Figure 3

(Color online) Bond-angle distribution functions of the liquid ${\text{Al}}_{60}{\text{Cu}}_{40}$ alloy at different temperatures, The data got from two different supercells at four different temperatures are also shown as dot.

Figure 4

(Color online) The statistics of the bond-pairs distribution of the liquid ${\text{Al}}_{60}{\text{Cu}}_{40}$ alloy at different temperatures, together with the topologic structures of some representative pair-types (brown balls are root pairs while green ones are near-neighbor atoms).

Figure 5

(Color online) The statistics of the most frequent VC types that appear in the model of the liquid ${\text{Al}}_{60}{\text{Cu}}_{40}$ alloy for three representative temperatures.

Figure 6

(Color online) The representative topologic structures of the most frequent clusters (ball and stick) as well as their Voronoi cells (full and dot lines).

Figure 7

The calculated frequency density of ${\widehat{W}}_6$ distributions of ${\text{Al}}_{60}{\text{Cu}}_{40}$ at $T=973\text{K}$ for 12 types of the most abundant polyhedra from Voronoi indices. The vertical lines indicate the ${\widehat{W}}_6$ values for the ideal icosahedral $\left(-0.169\right)$, fcc $\left(-0.013\right)$ and bcc (0.013) structures, as indicated on the figure. Note that the $⟨0,0,12,0⟩$ barely spans the ${\widehat{W}}_6$ value for an icosahedron.

Figure 8

(Color online) (a) The average coordination number of the liquid ${\text{Al}}_{60}{\text{Cu}}_{40}$ alloy. (b) The ratio between the CNs of the Al-centered and Cu-centered. (c) The distribution of average coordination number at 973, 1073, and 1323 K.

Figure 9

(Color online) (a) The Al-centered and (b) Cu-centered CN distribution at 973, 1073, and 1323 K.

Figure 10

(Color online) The self-diffusion constant $D$ plotted in logarithmic scale. The red lines are the linearly fitted results. The open and solid circles are from 100-atom and 200-atom simulations, respectively.

Figure 11

(Color online) (a) The average lifetimes for all the Voronoi clusters in ${\text{Al}}_{60}{\text{Cu}}_{40}$ at different temperatures; (b) The lifetime for the most frequent VC types that appears in the model of the liquid ${\text{Al}}_{60}{\text{Cu}}_{40}$ alloy for three representative temperatures.