Abstract
The effects of oxygen vacancy $({V}_{\mathrm{O}})$ and epitaxial strain on the ferroelectric (FE) and antiferrodistortive (AFD) properties of the [001]-oriented ${\mathrm{PbTiO}}_{3}/{\mathrm{SrTiO}}_{3}$ 1/1 superlattice are comprehensively studied using first-principles calculations. It is found that the oxygen vacancies form most easily when the superlattice in-plane lattice constant is between those of single-crystal ${\mathrm{PbTiO}}_{3}$ and ${\mathrm{SrTiO}}_{3}$. The polarization in the direction of the Ti-${V}_{\mathrm{O}}$-Ti chain is remarkably reduced due to the ${V}_{\mathrm{O}}$-induced local tail-to-tail polarization patterns, and consequently, the ${V}_{\mathrm{O}}$ can pin the polarization to a certain direction. Moreover, the octahedral rotation or tilting around the direction of the Ti-${V}_{\mathrm{O}}$-Ti chain is also suppressed while the rotations along the other two orthogonal directions are enhanced. In both perfect and oxygen-deficient superlattices, the ferroelectric phase has lower energy when the octahedra rotate around the polar axis. These results suggest a promising way to mediate the FE and AFD properties in oxygen-deficient superlattices.
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