The atomic structure of twin boundaries in rutile

The equilibrium atomic structure of the (101) and (301) twin boundaries in rutile (TiO 2 ) has been computed using an ionic shell model and compared with high resolution electron microscopy images of the same boundaries using image simulation. The lowest-energy (101) twin boundary structure is characterized by an in-plane translation of 1/2⟨111⟩ which conserves the mirror symmetry of the metal sublattice but which imposes a displacement on the oxygen sublattice. The lowest-energy (301) twin-boundary structure involves no in-plane translation and is characterized by mirror symmetry of both the metal and the oxygen sublattices. The computed mirror symmetry of the metal sublattice for both twin boundaries is in agreement with the electron microscopy observations. A small distortion present in the simulated images is discussed in terms of the interatomic potential used in the calculations.