Study of the FCC-BCC phase transition in an Au-Fe alloy

The properties of the disordered Au-Fe substitution alloy are studied based on the analytical method, which uses the paired interatomic potential of Mie–Lennard-Jones. The parameters of the 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. Under normal conditions (i.e., pressure $P=0$ and temperature $T$ = 300 K), changes in the properties of the Au-Fe alloy at the structural phase transition of FCC-BCC are calculated. Using the RP-model of the nanocrystal, the displacement of the $C_f$ concentration, at which the FCC-BCC phase transition occurs, due to a decrease in the size of the nanoparticle was calculated. It is shown that at an isochoric-isothermal decrease in the number of atoms $(N)$ in an Au-Fe nanoparticle, the $C_f$ value displace towards higher Fe concentrations. For a nanoparticle with a fixed number of atoms and a constant surface shape, the $C_f$ value increases at an isochoric increase in temperature, and the $C_f$ value decreases at an isothermal decrease in density. Calculations have shown that at $N<$ 59900 for the Au$_{1-C}$Fe$_{C}$ alloy at $P=0$, $T<$ 300 K and at any iron concentration, the FCC structure is more stable than the BCC structure.