Model-potential study of the lattice dynamics and elastic constants of the Ni0.55Pd0.45 alloy.

Abstract

A first-principles calculation has been done to compute the force constants of fcc Ni and Pd by applying the transition-metal model potential of Animalu. These force constants are derived up to 10 sets of nearest neighbors, and then a real-space analysis is done to study the dynamical behavior and elastic constants of the two d-band metals. A linear relation is used to compute the lattice constant of the alloy ${\mathrm{Ni}}_{0.55}$${\mathrm{Pd}}_{0.45}$. Next the force constants of the metals are evaluated at this lattice constant of the alloy. The lattice dynamics and elastic constants of the ${\mathrm{Ni}}_{0.55}$${\mathrm{Pd}}_{0.45}$ alloy are then computed by using the force constants and mass for the alloy, obtained by the concentration averages of the force constants and masses of the component metals. In each case, the present microscopic real-space analysis gives the phonon dispersion curves and elastic constants reasonably comparable with the available experimental data. Finally a three-body potential is incorporated in the lattice-dynamical calculation and in all cases, the transverse branches are improved. Thus on one hand, the present calculation explains the lattice dynamics and elastic constants of Ni, Pd, and ${\mathrm{Ni}}_{0.55}$${\mathrm{Pd}}_{0.45}$ alloy and, on the other, it shows that a mean-crystal model works well for the high-concentration alloy, ${\mathrm{Ni}}_{0.55}$${\mathrm{Pd}}_{0.45}$.