Magnéli-like phases in epitaxial anatase TiO ₂ thin films

Using high-resolution transmission electron microscopy and image simulation techniques in combination with ab initio calculations, we show the existence of two different superlattices of crystallographic shear planes, analogous to the Magnéli phases of rutile, in oxygen-deficient films of anatase TiO ₂ epitaxially grown on LaAlO ₃ substrates. (103)- and (101)-oriented shear plane structures are detected in the outer film region and in proximity of the film/substrate interface, respectively. We show that these shear planes are characterized by TiO-like cubic local structures, which can deviate from the Ti _nO _2n-1 stoichiometry of the classical rutile-derived Magnéli phases, particularly in the outer part of the film. Computed formation energies provide insights into the thermodynamic stability of the observed structures and their relations to the growth dynamics.