The experimental nuclear quadrupole interaction in synthetic Al-goethites of varying crystallinity

The effect of aluminum content and degree of crystallinity upon the possible values for both the polar coordinates (theta and phi) of the magnetic hyperfine field direction with respect to the electric field gradient (EFG) frame of reference and for the asymmetry parameter (eta) in synthetic Al-goethites was determined experimentally from their variable temperature Mossbauer spectra. The range of values for these parameters was examined using the ratio R of the quadrupole shift to the quadrupole splitting. It was found that R varies in the range -0.62 less than or equal to R less than or equal to -0.55, implying that, considering all the samples, similar to65degrees less than or equal to theta less than or equal to 90degrees, similar to-1 less than or equal to cos 2phi less than or equal to -0.25 and similar to0.1 less than or equal to eta less than or equal to 1. Additionally, the principal components of the EFG tensor and eta were calculated using the simple point charge model.