Epitaxially strained SnTiO₃ at finite temperatures

By combining the effective Hamiltonian approach and direct ab initio computation, we obtain the phase diagram of SnTiO₃ with respect to epitaxial strain and temperature. This demonstrates the complex features of the phase diagram and provides an insight into this system, which is a presumably simple perovskite. Two triple points, as shown in the phase diagram, may be exploited to achieve high-performance piezoelectric effects. Despite the inclusion of the degree of freedom related to oxygen octahedron tilting, the ferroelectric displacements dominate the structural phases over the whole misfit strain range. Finally, we show that SnTiO₃ can change from hard to soft ferroelectrics with the epitaxial strain.