Structural and spectroscopic investigation of (111) twins in barium titanate

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Abstract
The coherent (111) twin boundary in BaTiO3 has been investigated using quantitative high-resolution transmission electron microscopy and spatially resolved electron-energy-loss spectroscopy (EELS). Lattice images under different defocusing conditions were obtained and compared with simulated images for different structural models. An excellent match between calculated and observed images was obtained only for the model where the Ba-O3 plane constitutes the twin boundary. The oxidation state of Ti at twin boundaries was interrogated by studying the near-edge structure of the L23 ionization edge of Ti using spatially resolved EELS. The difference between spectra taken from the bulk and those including the boundary indicates the presence of Ti in a reduced oxidation state at the boundary. The charge is compensated by oxygen vacancies Vö in the twin plane, which is therefore composed of Ba-O3-x[Vö]x instead of Ba-O3.