Relation between incommensurate satellites and phonon softening in Ti-Ni-based shape memory alloys

In Ti-44.0 Ni-6.0 Fe alloy, diffuse satellites appear at incommensurate positions given by gB2 + q when the zone axis is [1 1 1] or [0 0 1], but not [1 1 0]. This result implies that the satellites appear because of a transverse wave consistent with the displacement of atoms in the <1 1 0> direction, which is perpendicular to the propagation vector q = <ζ ζ-bar 0>*, for ζ ∼ 1/3. This transverse wave occurs as a result of the phonon softening of the TA2 branch.