The new stable phases of Fe2Pd crystal alloy and their properties

This work presents a combination of particle swarm optimization crystal structure search method and first-principles calculations to investigate new stable crystal structures of Fe2Pd. Three structurally stable tetragonal phases (with space groups I4/mmm, P4/mmm, P4/nmm) and a structurally stable cubic phase (C15 Laves phase (Fd3¯m)) are predicted at 0 GPa. The enthalpy of formation reveals that these four phases are thermodynamically stable in the ferromagnetic state, and the tetragonal P4/nmm phase has the highest stability. Calculated phonon spectra indicates that the remaining three predicted structures are dynamically stable except for I4/mmm structure. From the elastic constant, all of the predicted structures are mechanically stable phases. Among these studied structures, the three tetragonal phases with similar values of bulk modulus have high uniaxial magneto-crystalline anisotropy, high thermal expansion coefficient, large bulk modulus, and good ductility. However, the cubic Fd3¯m phase is characterized by low magneto-crystalline anisotropy, small thermal expansion coefficient, high shear and Young's modulus, and brittleness. Finally, the high-pressure stability of these four structures is investigated. The theoretical prediction indicates a structural transition from tetragonal P4/nmm phase to ductile Fd3¯m structure at 26.8 GPa, while the I4/mmm is the most stable above 80 GPa.