Deviation of congruent composition in Fe-Pd system

摘要

The first-principles calculation of the disordered L10 phase boundary for the Fe-Pd system is attempted by com- bining the FLAPW electronic structure total energy calculations and the cluster variation method via the cluster expansion method. The lattice vibration effects are taken into account based on the Debye-Gruneisen model within quasi-harmonic approximation. The transition temperature is reproduced with very high accuracy. However, the experimental congruent composition of disordered L10 phase that significantly deviates from 1:1 stoichiometry is not reproduced. Further calcula- tions are attempted based on the phenomenological Lennard-Jones type pair potential, which is capable of introducing both tetragonality of the L10 ordered phase and additional configurational freedom because of the magnetic spins. The prelimi- nary calculations indicate that the tetragonality enhances the stability of the L10 ordered phase and the magnetic contribu- tions also change the transition temperature. Despite these findings, the shift of the congruent composition still remains as a subject that needs further research. The electronic origin of the shifting of the congruent composition is briefly discussed.