Uniaxial-stress dependence of the phonon behavior in the premartensitic phase ofNi62.5Al37.5

Results of neutron-scattering experiments on a single crystal of ${\mathrm{Ni}}_{62.5}$ ${\mathrm{Al}}_{37.5}$ as a function of uniaxial stress and temperature are reported. Emphasis is placed on the behavior of the low-energy part of the [ζζ0]-${\mathrm{TA}}_2$ phonon branch and its associated central peak. The dip in the phonon-dispersion curve is stress dependent and shifts from ζ=0.14 for zero stress to ζ=0.18 for an applied stress of 85 MPa at room temperature. As the temperature decreases the satellite shifts further, the phonon energy decreases considerably, and the linewidths become broad. These results are interpreted in terms of Clapp’s localized soft-mode theory of nucleation in martensite.