Phase separation behavior and magnetic properties of Li(FexAl1–x)5O8solid solutions

Abstract

Phase separation behaviour and magnetic properties of Li(Fe_xAl_1–x)₅O₈ solid solutions have been investigated. A single-phase Li(Fe_0.5Al_0.5)₅O₈ solid solution, which was quenched from 1250 °C, separated into Fe-rich and Al-rich solid solution phases with a continuous compositional variation when it was annealed at 1000 and 950 °C inside the chemical spinodal estimated using the theory of Cook and Hilliard. On the other hand, a Li(Fe_0.68Al_0.32)₅O₈ solid solution showed binodal-type phase separation after an incubation period of 200 h at 1000 °C inside the miscibility gap but outside the spinodal. The coercive force of the Li(Fe_0.5Al_0.5)₅O₈ solid solution spinodally decomposed at 1000 °C increased to 7.2 kA m^–1, which was about 9 times as large as that before annealing. Annealing of the Li(Fe_0.5Al_0.5)₅O₈ solid solution at 950 °C raised the coercive force to 8.6 kA m^–1. The increase in the coercive force is possibly due to the modulated structure which is characteristic of spinodally decomposed ceramics. The coercive force of the Li(Fe_0.68Al_0.32)₅O₈ solid solution remained constant even after it was annealed at 1000 °C for 200 h to decompose it binodally.