Position of Incommensurate Satellites Appearing in Ti-Ni Based Shape Memory Alloys
We have investigated electron diffraction patterns of a Ti-44Ni-6Fe alloy exhibitng a negative temperature dependence in electrical resistivity below Tmin = 210 K. The electron diffraction patterns taken near Tmin show diffuse satellites at gB2 + <zζ0>* when the zone axis is  and . For both the beam directions, the value ζ is slightly smaller than 1/3. On the other hand, the satellites are missing when the zone axis is . This means that the incommensurate phase has a modulated structure with the propagation vector <zζ0>* (ζ~1/3) and the displacement direction is one of <110> which is vertical to the propagation vector. This modulation is obviously the consequence of the phonon softening of TA2-branch with the propagation vector near <zζ0>* (ζ~1/3). In addition to the satellite at gB2 + <zζ0>* (ζ~1/3), satellites appear at gB2+<zζ0>* with ζ = 1/2 when the zone axis is  and rod-like steaks appear in <112>* direction when the zone axis is . However, these satellites and rod-like streaks do not show clear temperature dependence, suggesting they are not directly related to the phonon softening of TA2-branch.
Yves Bréchet, Emmanuel Clouet, Alexis Deschamps, Alphonse Finel and Frédéric Soisson
M. Todai et al., "Position of Incommensurate Satellites Appearing in Ti-Ni Based Shape Memory Alloys", Solid State Phenomena, Vols. 172-174, pp. 150-154, 2011