Theoretical prediction of solution in ScxY1–x Fe2 and order-disorder transitions in V2x Fe2(1–x)Zr

Abstract

Alloying is an important way to increase the diversity of material structure and properties. In this paper, we start from Ising model considering nearest neighbor interaction, in which a ferromagnetic system corresponds to a low temperature phase separation and high temperature solid solution of binary alloy, while antiferromagnetic system corresponds to a low temperature ordered solid solution and a high temperature disorder. The high-throughput first-principles calculation based on the structure recognition is realized by the program SAGAR (structures of alloy generation and recognition) developed by our research group. By considering the contribution of structural degeneracy to the partition function, theoretical prediction of alloy materials can be carried out at finite temperature. Taking hydrogen storage alloy (Sc_<i>x</i>Y_1–<i>x</i> Fe₂ and V_2<i>x</i> Fe_{2(1–<i>x</i>)}Zr) for example, the formation energy of ground state (at zero temperature) can be obtained by the first-principles calculations. It is found that the formation energy of Sc_<i>x</i>Y_1–<i>x</i> Fe₂ is greater than zero, thereby inducing the phase separation at low temperature. The free energy will decrease with the temperature and concentration increasing, where the critical temperature of solid solution of alloy is determined according to the zero point of free energy. The formation energies of V_2<i>x</i> Fe_{2(1–<i>x</i>)}Zr are all lower than zero, and the ordered phase occurs at low temperature. The order-disorder transition temperature of V_0.5Fe_1.5Zr and V_1.5Fe_0.5Zr are both about 100 K, while the transition temperature of VFeZr is nearly 50 K. The calculation process will effectively improve the high throughput screening efficiency of alloy, and also provide relevant theoretical reference for experimental research.