Nanotwins in BaTiO₃ nanocrystals

Abstract

BaTiO₃ nanocrystals, in which the coexistence of the high-temperature hexagonal phase with the cubic—tetragonal phase at room temperature was suggested in a previous study, have been investigated using high-resolution transmission electron microscopy. The BaTiO₃ nanocrystals were found to have the cubic—tetragonal structure with (111) planar defects. The observed images other than cubic—tetragonal BaTiO₃ showed firstly coherent (111) twins often forming lamellae consisting of three to five atomic layers, secondly periodic images of a 0.70 nm × 0.49 nm rectangle and thirdly incoherent (111) planar images. The rectangular lattice and the incoherent (111) planar images originated from the superimposition of the matrix and the (111) twin. The peaks that were ascribed to the hexagonal phase in the electron diffraction pattern were well explained as a result of the nano-sized twins in the cubic—tetragonal matrix.