The electrical hyperfine parameters in synthetic aluminogoethites.

The effects of the aluminum substitution and degree of crystallinity upon the lattice-dynamical and electrical properties of synthetic goethites are determined from their Mossbauer spectra. The temperature variations of the centre shift could be calculated using the Debye approximation for the lattice vibrations. The parameters incorporated in this model exhibit a maximum at a certain aluminum content within each of the four series in this study. It has been found that the principal axis of the EFG remains perpendicular to the direction of the magnetic hyperfine field when the aluminum content and/or the crystallinity change.