Phase Transformation Kinetics in the Doped System LiAl ₅ O ₈ —LiFe ₅ O ₈

Abstract

Solid solutions of various compositions in the system LiAl 5 O 8 –LiFe 5 O 8 were prepared by calcining mixtures of Li 2 CO 3 , Al 2 O 3 , and Fe 2 O 3 . Lattice parameters of the solid solutions were determined by X‐ray diffraction (XRD). Samples of equimolar composition were also prepared with titanium and magnesium as dopants. The doped and undoped samples were annealed at 1050°C for up to 192 h in air. Annealing at this temperature, which is inside the miscibility gap for an equimolar composition, led to the decomposition of the originally single‐phase solid solution. The extent of phase transformation was followed by XRD. The fraction transformed was estimated using integrated peak intensities. The kinetic data were analyzed in light of the conventional kinetic equation and the previously derived equation which takes into account the diffusive and the interface transfer processes. It was observed that titanium enhances and magnesium suppresses the kinetics of phase separation. These results are rationalized on the premise that the predominant point defects are Schottky defects in this spinel system.