An Electron Diffraction Study and a Theory of the Transformation from γ-Fe₂O₃to α-Fe₂O₃

Abstract

Phase transformation of γ-Fe 2 O 3 to α-Fe 2 O 3 was studied by electron diffraction. Above 400°C γ-Fe 2 O 3 is transformed to α-form which consists of twins. The orientation relationship of the transformation is (111) γ //(0001) α and [1\bar10] γ //[01\bar10] α . The twinning plane of transformation product was determined to be basal or (01\bar10) Plane. The transformation mechanism consists of the re-stacking of close-packed oxygen ion layers and the synchronous displacement of ferric ions located at the interstices of oxygen. These cooperative movements are discussed by dislocation models.