Rhombohedral Twin Structure in Hematite (α-Fe₂O₃)

Abstract

Electron optical imaging of the structure of haematite ( α-Fe₂O₃) in two projections has allowed the microscopic twinning elements of rhombohedral twins to be determined. A systematic analysis of alternative structural models, using computer-simulation and image-matching considerations, as well as crystallochemical arguments, is presented. The twin has a screw operation consisting of a pure rotation of 180º about [0111], the twinning direction, combined with a parallel translation of (1/22) [0111]. The twinning plane (0112) forms a coherent interface, consisting of face-and edge-shared octahedra , with no change in the normal nearest-neighbour coordination.