Direction of atom displacement in incommensurate state of Ti–32Pd–18Fe shape memory alloy

• Displacement of atoms causing diffuse satellites in a Ti–32Pd–18Fe alloy (in at%) has been investigated by transmission electron microscopy (TEM).
• The movement of atoms in the IC phase in this alloy can be described as a transverse wave with the propagation vector q=〈ζζ¯0〉⁎ with ζ∼1/5 and the displacement of atoms is in the [110] direction.
• The obtained results imply that the IC phase in Ti based shape memory alloys is a result of phonon softening in the TA2 branch.

Displacement of atoms causing diffuse satellites in a Ti–32Pd–18Fe alloy (in at%) has been investigated by transmission electron microscopy (TEM). In this alloy, diffuse satellites appear at incommensurate positions given by gB2+q when the zone axis is [111] and [001], but they are missing when [110]. This results imply that the satellites appear because of a transverse wave with a propagation vector of q∼1/5〈ζζ¯0〉⁎ and displacement in 〈110〉 direction. Possibly, this transverse wave occurs as a result of phonon softening of the TA2 phonon branch, which is a common feature for B2-type Ti-based shape memory alloys.