  The modulated structure of the martensite phase of Ni2MnGa is revisited using
high resolution synchrotron x-ray powder diffraction (SXRPD) measurements,
which reveals higher order satellite reflections up to the 3rd order and phason
broadening of the satellite peaks. The structure refinement, using the (3+1)
dimensional superspace group approach, shows that the modulated structure of
Ni2MnGa can be described by orthorhombic superspace group Immm(00$\gamma$)s00
with lattice parameters a= 4.21861(2) {\AA}, b= 5.54696(3) {\AA}, and c=
4.18763(2) {\AA} and an incommensurate modulation wave vector q= 0.43160(3)c*=
(3/7+$\delta$)c*, where $\delta$=0.00303(3) is the degree of incommensuration
of the modulated structure. Additional satellite peak broadening, which could
not be accounted for in terms of the anisotropic strain broadening based on a
lattice parameter distribution , has been modeled in terms of phasons using
fourth rank covariant strain tensor representation for incommensurate
structures. The simulation of single crystal diffraction patterns from the
refined structural parameters unambiguously reveals a rational approximant
structure with 7M modulation. The inhomogeneous displacement of different
atomic sites on account of incommensurate modulation and the presence of phason
broadening clearly rule out the adaptive phase model proposed recently by
Kaufmann et al.[1] and suggests that the modulation in Ni2MnGa originates from
soft-mode phonons.
