The (210)[½¼½] crystallographic shear planes which occurred in gallia-doped rutile were examined at 3.2Å resolution. At low dopant levels, isolated pairs of (210) boundaries having well-defined spacings of 4.8Å and a stoichiometry of Ga4TiO8 occurred. At higher dopant levels, single boundaries which were regularly spaced and up to 35Å apart, formed members of an homologous series of structures: Ga4Tim-4O2m-2. Even in the ordered structures, low concentrations of Ga4TiO8 defect pairs occurred. The latter were sometimes associated with voids in the structure. A mechanism for the splitting of pairs into separate single faults was proposed. This allowed the sideways movement and ordering of single boundaries. An image of the dislocation structure at the termination of a Ga4TiO8 pair inside an ordered structure, Ga4Ti25O56, provided the first evidence that the crystallographic shear planes were extrinsic, involving the insertion of extra metal atoms, rather than intrinsic and involving oxygen removal from sites within the crystal. It was shown that the Burgers vector of the dislocation terminating the defect pairs was [0½0]. This resolved an apparent discrepancy between displacement vector determinations giving [0½0] for isolated faults, and those which found [½¼½] for single boundaries in ordered Ga4Tim-4O2m-2.

High-Resolution Electron Microscopy of (210) Defect Pairs in Gallia-Doped Rutile. Stone, G.G., Bursill, L.A.: Philosophical Magazine, 1977, 35[5], 1397-412