Clarification of origin of positive excess volume of Pd–Fe binary alloys by using first-principles calculations and HAXPES

Abstract

Disordered Pd–Fe alloys show a positive excess-volume effect, contrary to the predictions of the Iida–Guthrie model. The effect becomes larger at a composition of approximately Pd0.5Fe0.5. The origin of the positive excess-volume effect was investigated by using first-principles calculations to study the electronic structures in the ordered and disordered states of Pd–Fe alloys with two different compositions, i.e., Pd0.53Fe0.47 and Pd0.75Fe0.25. The calculated partial density of states for the disordered state in Pd0.53Fe0.47 indicates weakening of Pd metallic bonds because of fully occupied 4d majority-spin states with enhanced anti-bonding characteristics, which cause an increase in the volume. In addition, the magneto-volume effect, which minimizes the increase in the electronic kinetic energy caused by exchange splitting, contributes to the positive excess volume. The calculated electronic states and those obtained from hard X-ray photoelectron spectra were consistent with each other.