The perovskite $\mathrm{BaSn}{\mathrm{O}}_3$ has an Sn $s$-orbital conduction band minimum, which makes it of interest as a transparent-conducting oxide parent compound but also contraindicates the ferroelectric instability characteristic of the related compound $\mathrm{BaTi}{\mathrm{O}}_3$. In this work, we studied the effect of (001) compressive strain on $\mathrm{BaSn}{\mathrm{O}}_3$ using first-principles methods. We found that, with low compressive strain, symmetry breaking takes cubic $\mathrm{BaSn}{\mathrm{O}}_3$ to a nonpolar tetragonal state, with a first-order phase transition to a hidden highly polarized ferroelectric supertetragonal state at ∼−5%. Based on the facts that the mismatch of the lattice constant in experiment between $\mathrm{BaSn}{\mathrm{O}}_3$ and $\mathrm{SrTi}{\mathrm{O}}_3$ is ∼−5.2% and coherent growth of $\mathrm{BaSn}{\mathrm{O}}_3$ on $\mathrm{SrTi}{\mathrm{O}}_3$ has been experimentally realized for $\mathrm{BaSn}{\mathrm{O}}_3$ layers thinner than 3 unit cells, we studied a series of $\mathrm{SrTi}{\mathrm{O}}_3/\mathrm{BaSn}{\mathrm{O}}_3$ superlattices with 1 or 2 unit cells of $\mathrm{BaSn}{\mathrm{O}}_3$ and several unit cells of $\mathrm{SrTi}{\mathrm{O}}_3$. We found that the superlattices are ferroelectric with large polarizations. We propose that the origin of ferroelectricity in the superlattices is the mechanical and electrical coupling of the $\mathrm{BaSn}{\mathrm{O}}_3$ and $\mathrm{SrTi}{\mathrm{O}}_3$ layers, with the polarized supertetragonal state of $\mathrm{BaSn}{\mathrm{O}}_3$ induced by compressive strain from the $\mathrm{SrTi}{\mathrm{O}}_3$ layers and polarization of the $\mathrm{SrTi}{\mathrm{O}}_3$ layers by the polar $\mathrm{BaSn}{\mathrm{O}}_3$ layers. Due to the distinctive electronic states in the $\mathrm{BaSn}{\mathrm{O}}_3$ layers, the realization of ferroelectricity holds promise for the design of electronic devices.

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• Dielectric properties
• Electric polarization
• Ferroelectric phase transition
• Heterostructures
• Perovskites
• Density functional theory