  Iron-based superconductor SmFeAsO(0.91)F(0.09) has been investigated by the
57Fe Moessbauer spectroscopy versus temperature with the special attention paid
to the region of the superconducting transition at about 47 K. Modulation of
the electron charge density was found. It leads to the development of the
charge density wave (CDW) and electric field gradient wave (EFGW). The
modulation of CDW is enhanced in the temperature region of the superconducting
gap opening, while the amplitude of EFGW is partly suppressed within this
temperature region. This effect is exactly opposite to the similar effect in
Ba(0.6)K(0.4)Fe2As2 superconductor. Hence, it seems that d electrons contribute
significantly to the Cooper pair formation in both compounds as EFGW is
perturbed within the temperature region of the superconducting gap formation.
