Cristallochemical characterization of synthetic Zn-substituted maghemites (γ-Fe2-xZnxO3)

Maghemite (gamma-Fe2O3) is the most usually found ferrimagnetic oxide in red basalt-derived soils. The variable degrees of ionic substitution of Fe3+ for different metals (e.g. Ti4+, Al3+, Mg2+, Zn2+, and Mn2+) and non-metals in the maghemite structure influence some cristallochemical features of this iron oxide. In this study, synthetic Zn-substituted maghemites were prepared by co-precipitation in alkaline aqueous media of FeSO4 center dot 7H(2)O with increasing amounts of ZnSO4 center dot 7H(2)O to obtain the following sequence of Fe3+ for Zn2+ substitutions: 0.0, 0.025, 0.05, 0.10, 0.15, 0.20, and 0.30 mol mol(-1). The objective of this work was to evaluate the cristallochemical alterations of synthetic Zn-substituted maghemites. The dark black synthetic precipitated material was heated to 250 degrees C during 4 h forming a brownish maghemite that was characterized by chemical analysis as well as X ray diffraction (XRD), specific surface area and mass-specific magnetic susceptibility. The isomorphic substitution levels observed were of 0.0013, 0.0297, 0.05909, 0.1145, 0.1764, 0.2292 and 0.3404 mol mol(-1), with the formation of a series of maghemites from Fe2Zn0O3 to Fe(1.49)Zn(0.770)O3. The increase in Fe3+ for Zn2+ substitution, [Zn mol mol(-1)] increased the dimension a(0) of the cubic unit cells of the studied maghemites according to the regression equation: a(0) = 0.8343 + 0.02591Zn (R-2 = 0.98). On the other hand, the mean crystallite dimension and mass-specific magnetic susceptibility of the studied maghemites decreased with increasing isomorphic substitution.