The grain boundary structure of a [001] symmetrical tilt boundary with a tilt angle of 66° was investigated by using a rutile-type TiO2 bicrystal. The tilt angle of this boundary had a misfit angle of 1.7º from exact Σ13; approaching Σ17. High-resolution transmission electron microscopy revealed that the boundary was free from any secondary phases, and that the 2 single crystals contacted each other perfectly at the atomic scale. The boundary exhibited almost straight features, without any step structures, whereas part of the boundary formed facet structures consisting of low-index planes such as {310} and {110}. It was found, by weak-beam dark-field observations, that contrasts due to strong strain fields existed on the grain-boundary plane; with a spacing of 7.6nm. Comparison with atomic structural analysis, using high-resolution transmission electron microscopy, showed that the strain field resulted from a distorted Σ13 unit structure; which could be predicted from a rigid body model of Σ13. This distorted unit structure had a similar structure to Σ17. That is, the boundary consisted of a periodical array that comprised mainly Σ13 unit structures and some Σ17-like unit structures. Thus, a misfit angle in this boundary was not accommodated by introducing secondary dislocations, but by transformation of the basal unit structure.

High Resolution Microscopy Study for [001] Symmetric Tilt Boundary with a Tilt Angle of 66° in Rutile-type TiO2 Bicrystal. T.Ohno, S.Ii, N.Shibata, K.Matsunaga, Y.Ikuhara, T.Yamamoto: Materials Transactions, 2004, 45[7], 2117-21