Nanoscale local structures of rhombohedral symmetry in the orthorhombic and tetragonal phases of BaTiO3 studied by convergent-beam electron diffraction

The symmetries of the rhombohedral, orthorhombic, and tetragonal phases of barium titanate (BaTiO3) are investigated using convergent-beam electron diffraction. Nanometer-sized local structures with rhombohedral symmetry are observed in both the orthorhombic and tetragonal phases. This indicates that an order-disorder character exists in phase transformations of BaTiO3. The nanostructures in these phases are discussed in terms of an order-disorder model with off-centered Ti in the < 111 > directions.