Phase transitions and domain structures in strained pseudocubic (100)SrTiO3thin films

Abstract

The mutual interactions between a structural transition and a ferroelectric transition are analyzed for different strain states in a pseudocubic (100) $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ film by examining the equilibrium solutions of the total free energy as a function of polarization, strain and structural order parameter. The range of possible ferroelectric transition temperatures and the possible ferroelectric states of a strained $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ film are determined with respect to the variation in the reported properties of bulk $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ single crystals. The ferroelectric and structural domain morphologies at a biaxial tensile strain ${e}_{0}=0.94%$ were predicted using phase-field simulations. It is shown that variations in the reported values of bulk properties and in the Landau energy coefficients from different literature sources lead not only to a wide range of possible transition temperatures at a given strain, but also to different ferroelectric states (e.g., polarization along the pseudocubic ⟨110⟩ vs ⟨100⟩ directions) thus different domain structures under a biaxial tensile strain. Both optical second harmonic generation and confocal scanning optical microscopy measurements demonstrate that the domain states in $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ films strained at ${e}_{0}=0.94%$ and 1.16% exhibit polar directions along the pseudocubic ⟨110⟩ directions within the pseudocubic (001) plane of the film.