Spinodal Decomposition in the System CoFe ₂ O ₄ ‐Co ₃ O ₄

Abstract

A miscibility gap exists in the spinel‐structured region of the pseudobinary CoFe 2 O 4 ‐CO 3 O 4 system in air. Phase decomposition inside the miscibility gap was investigated by transmission electron microscopy and by X‐ray diffraction. In samples containing 35 and 50 cation % Fe, the first observable changes on aging at 500°C were appearance of side bands on X‐ray diffraction photographs of powder samples and of a periodic structure under the electron microscope. When specimens which contained 50 cation % Fe were aged at 700°C, the first observed change was another set of diffraction lines; homogeneously distributed fine particles were also observed. The former behavior was attributed to spinodal decomposition and the latter to classical nucleation and growth.