Phase separation behavior and magnetic properties of Li(FexAl1–x)5O8solid solutions
Abstract
Phase separation behaviour and magnetic properties of Li(FexAl1–x)5O8 solid solutions have been investigated. A single-phase Li(Fe0.5Al0.5)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(Fe0.68Al0.32)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(Fe0.5Al0.5)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(Fe0.5Al0.5)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(Fe0.68Al0.32)5O8 solid solution remained constant even after it was annealed at 1000 °C for 200 h to decompose it binodally.