Study by electrical conductivity of the process of oxidation and of the change of structure in synthetic titanomagnetites

Abstract

During oxidation in air of submicronic synthetic titanomagnetites (Fe 2+ 1+ x Fe 3+ 2−2 x Ti 4+ x )O 2− 4 (0 < x < 0.82) the temperature dependence of the electrical conductivity over a temperature range 300–1000 K was investigated. Below 700 K the titanomagnetites are oxidized in cation deficient spinels and the evolution of electrical conductivity might be closely associated with the position and the oxidation degree of iron cations in the spinel lattice. The profile of the σ = f( t) curves shows that the mechanism of electrical conduction can be related to the electronic exchange between the Fe 2+ and Fe 3+ ions in octahedral as well as tetrahedral positions of the spinel lattice. Above 700 K, the electrical conductivity yields discontinuities in the log σ = (f( 1 T ) curves attributed to the generation of new phases of α-Fe 2O 3, TiO 2, and Fe 2TiO 5. Titanium does not appear to have a stabilizing effect on the phase change.