Changes in the structure of the Au–Fe alloy with a change in the concentration and with a decrease of the nanocrystal size

Abstract

An analytical method is proposed for calculating the properties of a disordered Au–Fe substitution alloy both with fcc and with bcc structures. The parameters of the Mie–Lennard-Jones pairwise interatomic potential for the fcc and bcc structures of Au and Fe are determined. Based on these parameters, the concentration dependences of the properties of the fcc and bcc structures of the Au–Fe alloy are calculated. It is shown that the concentration dependences are nonlinear and agree with the results obtained for fcc-Au-Fe by using density functional theory method. The changes in the lattice properties of the Au–Fe alloy under the fcc-bcc structural phase transition at a pressure of P = 0 and a temperature of T = 300 K are calculated. Based on the changes in the properties at the fcc-bcc transition, it is concluded that iron plays a major role in the phase transition in the Au–Fe alloy. The appearance of a metastable amorphous structure in a wide range of concentrations around the fcc-bcc transition in an Au–Fe alloy was explained. In the framework of the RP-model of a nanocrystal, the displacement of the iron concentration (Cf), at which the fcc-bcc phase transition occurs, due to a decrease in the nanocrystal size was calculated. It is shown that at an isochoric-isothermal decrease of the atoms number (N) in an Au–Fe nanocrystal, the Cf value increases. For a nanocrystal with a fixed of atoms number and a constant surface shape, the Cf value increases at an isochoric increase in temperature, and the Cf value decreases at an isothermal decrease in density. Calculations have shown that at N < 59 900 for the Au1–CFeC alloy at P = 0, T ≤ 300 K and at any iron concentration, the fcc structure of the nanocrystal is more stable than the bcc structure.