Phase Separation in the System (Fe,Mn)O

Transmission electron microscopy was used to observe variations in composition in single crystals of Fe _y Mn_{1– y} O_{1+] x} on a scale of 100 to 500 Å. Compositional fluctuations were resolved as lamellar-like striations oriented primarily in the 100] direction. Specimens had been equilibrated at 900°C in oxygen partial pressures within the monoxide phase region and then quenched to room temperature. A region of solid-solid immiscibility in the monoxide phase field is proposed. A different submicrostructure resulted from low-temperature decomposition (150°C) due to localized heating when samples were prepared by ion-bombardment thinning.