Investigation of structural states and oxidation processes in Li0.5Fe2.5O4−δ using TG analysis

Using the methods of X-ray phase and DSC analyses, a correlation is established between ordering/disordering of the structure of lithium pentaferrite (LPF—Li0.5Fe2.5O4−δ) and its nonstoichiometry with respect to oxygen. Ferrite specimens with a reduced content of oxygen were prepared by thermal annealing in vacuum (P = 2 × 10−4 mmHg). It is shown that this treatment results in oxygen nonstoichiometry and causes a transition of LPF into a state with random distribution of cations in the crystal lattice. Using nonisothermal thermogravimetry (TG), the kinetic dependences of oxygen absorption by the anion-deficient LPF are investigated within the temperature interval T = (350–640) °C in the course of its oxidation annealing in air. The kinetic experiment data are processed with the Netzsch Thermokinetics software. The oxidation rate constants, the effective coefficients, and the activation energy of oxygen diffusion in the material under study are derived. Their values are in a satisfactory agreement with those earlier obtained for the lithium–titanium ferrite ceramic material of the following composition: Li0.649Fe1.598Ti0.5Zn0.2Mn0.051O4−δ. The effective activation energy of oxygen diffusion in LPF calculated within the temperature interval T = (350–640) °C is found to be Ed = 1.88 eV. In its value, it is close to the activation energy of oxygen diffusion along grain-boundaries in the lithium–titanium ferrite ceramic material.