First-principles study of misfit strain-stabilized ferroelectric SnTiO ₃

Toxicity of lead and bismuth has motivated an active search for isovalent ferroelectric oxides free of these elements. Using first-principles density-functional calculations, we survey Sn(ii) titanates with SnTiO ₃ stoichiometry to evaluate the phase stability of polar and nonpolar polymorphs: we predict a tetragonal perovskite P4mm phase with a large axial ratio (c/a=1.134) and ferroelectric polarization (1.28 C/m2) to be the ground-state equilibrium structure. We also show that heteroepitaxial thin films of perovskite SnTiO ₃ promote the stereochemical lone-pair activity and simultaneously enable control over the direction of the net electric polarization and magnitude of the electronic band gap. Finally, we examine the consequence of antisite defects on the polar cation displacements by studying the substitution of Sn on Ti sites. We demonstrate that local metallic screening resulting from site substitution diminishes the magnitude of the polar distortions but does not completely quench it. Based on these calculations, we suggest that polar perovskite SnTiO ₃ ferroelectrics are viable thin-film alternatives to Pb- and Bi-containing oxides.