Phase transitions and domain structures in strained pseudocubic (100) SrTiO3 thin films

The mutual interactions between a structural transition and a ferroelectric transition are analyzed for different strain states in a pseudocubic (100) SrTiO3 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 SrTiO3 film are determined with respect to the variation in the reported properties of bulk SrTiO3 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 SrTiO3 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.