X-ray investigation of the premartensitic phase in ${\mathrm{Ni}}_{46.8}$${\mathrm{Ti}}_{50}$${\mathrm{Fe}}_{3.2}$

In the shape-memory alloy, NiTi:Fe, the martensitic transformation is well separated from the premartensitic (PM) phase and the latter can be studied in detail. X-ray diffraction studies in the PM phase reveal satellites near ${\overrightarrow{q}}_I=\frac{1}{3}(0,\overline{1},1)$ and ${\overrightarrow{\mathrm{q}}}_{\mathrm{II}}=\frac{1}{3}\mathrm{}(1,1,1)\mathrm{}$. For both $q$ values, the satellites are incommensurate and the surprising feature observed is that the incommensurate wave vector $\overrightarrow{\delta }$ and the width of the satellites depend upon the Brillouin zone studied. This contradicts a simple condensed charge-density and/or lattice-wave description of the PM phase. If the shift is neglected, the structure in the PM phase can be explained by a condensation of three [$\zeta \overline{\zeta }0$]${\mathrm{TA}}_2$ modes with $\zeta =\frac{1}{3}$. In addition we propose a relationship between the well-known $\omega$ phase and the PM phase observed in this experiment and for other alloys.