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 (Θ and ϕ) of the magnetic hyperfine field direction with respect to the electric field gradient (EFG) frame of reference and for the asymmetry parameter (η) in synthetic Al-goethites was determined experimentally from their variable temperature Mössbauer 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≤R≤−0.55, implying that, considering all the samples, ∼65°≤Θ≤90°, ∼−1≤cos 2ϕ≤−0.25 and ∼0.1≤η≤1. Additionally, the principal components of the EFG tensor and η were calculated using the simple point charge model.