Epitaxial (100), (110), and (111) BaTiO3 films on SrTiO3 substrates — A transmission electron microscopy study
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Chemical solution deposition (CSD) is a versatile method to fabricate oxide films. Here, the structure and local variations in the chemical composition of BaTiO3 (BTO) films prepared by CSD on (100), (110), and (111) SrTiO3 (STO) substrates were examined by transmission electron microscopy. The films were shown to be epitaxial and the relaxation of the films occurred by the formation of edge dislocations at the substrate–film interfaces. The Burgers vectors of the dislocations were determined to be a⟨010⟩, a[11¯0] and a, and a⟨110⟩ for the (100), (110), and (111) films, respectively. Due to the difference in thermal expansion between STO and BTO, the films are demonstrated to be under tensile strain. Furthermore, the boundaries between each deposited layer in the BTO films were found to be Ba-deficient in all cases. In the case of the (111) oriented film, defects like an anti-phase boundary or a thin layer with a twinned crystal structure were identified at the boundary between each deposited layer. Moreover, a larger grain was observed at the film surface with a twinned crystal structure. The interdiffusion length of A-cations at the STO–BTO interface, studied by electron energy-loss spectroscopy, was found to be 3.4, 5.3, and 5.3 nm for the (100), (110), and (111) oriented films, respectively. Interdiffusion of cations across the STO–BTO interface was discussed in relation to cation diffusion in bulk BTO and STO. Despite the presence of imperfections demonstrated in this work, the films possess excellent ferroelectric properties, meaning that none of the imperfections are detrimental to the ferroelectric properties.