Non-classical twinning of alumina precipitates in rutile

Abstract

Electron diffraction and conventional transmission electron microscopy results are presented which reveal that alumina-doped rutiles (Ti,Al)O_1·9961 contain alumina precipitates about 0·5 μm in diameter after application of a [111]_R† compressive stress at 1323K. The precipitates grow with bilateral heart-shaped symmetry about the plane of maximum resolved shear stress (111)_R. They exhibit a non-typical twin composition plane (1216)_α which is parallel to (110)_R and which bisects the precipitates parallel to the invariant twin plane, thus minimizing long-range elastic strains.