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Epitaxial growth of complex oxides on large-area wafers, such as sapphire and silicon, represents a key step toward scalable oxide device production. Solid phase epitaxy allows the synthesis of γ-Al2O3 on α-Al2O3 and provides a template with a matched lattice constant and appropriate cubic symmetry for subsequent heteroepitaxial growth of perovskite complex oxides. Nb-doped SrTiO3 thin films were deposited epitaxially on (111)-oriented γ-Al2O3 intermediate layers on (0001) c-axis-oriented sapphire α-Al2O3 crystals using pulsed laser deposition. The Nb:SrTiO3 thin films with a thickness of 53 nm, grown at 700 °C on γ-Al2O3, reached fully relaxed lattice parameters and were epitaxially oriented with respect to the substrate. Nb:SrTiO3 layers deposited using identical deposition conditions directly on α-Al2O3, without the γ-Al2O3 intermediate layer, were polycrystalline. The sheet conductivity of Nb:SrTiO3 grown on γ-Al2O3/α-Al2O3 is more than ten times higher than that of Nb:SrTiO3 grown directly on α-Al2O3 without the γ-Al2O3 layer. The results point to new directions for the integration of (111)-oriented pseudocubic perovskite complex oxides and the integration of epitaxial complex oxides over larger areas using α-Al2O3 single-crystal substrates. 

Amorphous BaTiO3 layers deposited on SrTiO3 (001) substrates at room temperature were subsequently crystallized using solid phase epitaxy (SPE). Heating an initially amorphous BaTiO3 layer in air at 650 °C for 3 h resulted in crystallization with components in two distinct crystallographic orientation relationships with respect to the substrate. Part of the volume of the BaTiO3 layer crystallized in a cube-on-cube relationship with the substrate. Other volumes crystallized in four variants of a 70.5° rotation about ⟨110⟩, resulting in a ⟨221⟩ surface normal in each case. Each of these four variants forms a Σ = 3 coincident site lattice with respect to the SrTiO3 substrate and the cube-on-cube oriented BaTiO3. Heating for the same duration and temperature in a reducing gas atmosphere resulted in the formation of polycrystalline BaTiO3 with no preferred crystallographic orientation. The dependence on the gas atmosphere indicates that it may be possible to tune the annealing time, temperature, and atmosphere to produce a single crystalline BTO on STO by SPE or produce a desired distribution of orientations. 

Abstract Above‐bandgap femtosecond optical excitation of a ferroelectric/dielectric BaTiO₃/CaTiO₃superlattice leads to structural responses that are a consequence of the screening of the strong electrostatic coupling between the component layers. Time‐resolved X‐ray free‐electron laser diffraction shows that the structural response to optical excitation includes a net lattice expansion of the superlattice consistent with depolarization‐field screening driven by the photoexcited charge carriers. The depolarization‐field‐screening‐driven expansion is separate from a photoacoustic pulse launched from the bottom electrode on which the superlattice is epitaxially grown. The distribution of diffracted intensity of superlattice X‐ray reflections indicates that the depolarization‐field‐screening‐induced strain includes a photoinduced expansion in the ferroelectric BaTiO₃and a contraction in CaTiO₃. The magnitude of expansion in BaTiO₃layers is larger than the contraction in CaTiO₃. The difference in the magnitude of depolarization‐field‐screening‐driven strain in the BaTiO₃and CaTiO₃components can arise from the contribution of the oxygen octahedral rotation patterns at the BaTiO₃/CaTiO₃interfaces to the polarization of CaTiO₃. The depolarization‐field‐screening‐driven polarization reduction in the CaTiO₃layers points to a new direction for the manipulation of polarization in the component layers of a strongly coupled ferroelectric/dielectric superlattice.