Cation distribution in synthetic titanomaghemites

Because of the difficulties of laboratory simulation of maghemitization, few studies have been carried out and the results of such studies are not in good agreement. Of particular interest is the evolution of the cation distribution with degree of non-stoichiometry. This indicates how the maghemitization process takes place at the atomic level. In the present study a suite of titanomagnetite specimens containing a range of concentration of Mg²⁺ ions were maghemitized and the possible cation distribution inferred from saturation magnetization measurements. Although a unique cation distribution cannot be obtained from such measurements, the observed data are consistent with the following model, except for high degrees of oxidation and high Mg concentration: (1) Ti⁴⁺ and vacancies in B sites only; (2) a random distribution of Mg²⁺ which remains frozen in during maghemitization; (3) availability for oxidation of tetrahedral site Fe²⁺ 20% of that of octahedral site Fe²⁺; and (4) deficient moment of the oxidized specimens due to small particle size.