DFT calculations of structural, magnetic, and stability of FeNiCo-based and FeNiCr-based quaternary alloys

As the Cantor-derived medium-entropy alloys (MEAs), FeNiCoMn and FeNiCrMn quaternaries in both equiatomic and non-equiatomic compositions were investigated by density functional theory combined with the quasiharmonic Debye-Grüneisen approximation using the special-quasirandom structure model. The structural properties, magnetic properties, and thermodynamics and phase stability were explored in detail. The temperature stabilization effect of lattice vibration, configurational mixing entropy, and thermal electronic excitation was discussed. Also FeNiCoPd and FeNiCrPd quaternaries, in which Mn was replaced by Pd, were considered in the same framework in order to highlight the similarities and differences between these Mn- and Pd-MEAs. The phase stability competition between homogeneous and inhomogeneous states in terms of both size and chemical ordering was revealed for four groups of FeNiCoMn, FeNiCoPd, FeNiCrMn, and FeNiCrPd MEAs.