Compositional variation of the phonon dispersion curves of bcc Fe-Ga alloys

Inelastic neutron scattering techniques have been used to measure the phonon dispersion curves of bcc Fe1-xGax (x=10.8, 13.3, 16.0, 22.5) alloys as a function of Ga concentration. The phonon frequencies of every branch were found to decrease significantly with increasing Ga concentration. The softening was most pronounced for the T-2[xi xi 0] branch and, to a lesser extent, the L[xi xi xi] branch in the vicinity of xi=2/3. The concentration dependence of the shear elastic constant C-'=1/2(C-11-C-12), calculated from the slope of the T-2[xi xi 0] branch, was found to agree with the results of sound velocity measurements. For the higher concentration sample measured, 22.5 at. % Ga, new branches appeared, an effect associated with the increase in the number of atoms per unit cell.