High Resolution Microscopy Study for [001] Symmetric Tilt Boundary with a Tilt Angle of 66° in Rutile-type TiO<SUB>2</SUB> Bicrystal

Abstract

In this study, the grain boundary structure of [001] symmetric tilt boundary with a tilt angle of 66 � was investigated using a rutile-type TiO2 bicrystal. The tilt angle of this boundary has a misfit angle of 1.7 � from an exact � 13 approaching to � 17 relation. High-resolution transmission electron microscopy study (HRTEM) has revealed that the grain boundary was free from any secondary phases, and the two single crystals contact each other perfectly at an atomic scale. The boundary shows almost straight feature without any step structures whereas a part of the boundary forms facet structures consisting of low index planes such as {310} and {110}. On the other hand, it was found that the contrasts due to strong strain fields existed on the grain boundary plane with a spacing of 7.6 nm by weak beam dark field observation. Comparing with atomic structural analysis using HRTEM, the strain field results from a distorted � 13 unit structure, which can be predicted from a rigid body model of � 13 relation. This distorted unit structure has a similar structure of � 17 relation. Namely, the boundary consists of a periodical array consisting mainly of � 13 unit structures and partially � 17-like unit structures. In other words, a misfit angle in this boundary was accommodated by not introducing secondary dislocations, but a transformation of basal unit structure.