Room-Temperature Ferroelectricity of Paraelectric Oxides Tailored by Nano-Engineering.

Inducing clear ferroelectricity in the quantum paraelectric SrTiO 3 is important for triggering methods to discover hidden phases in condensed matter physics. Several methods such as isotope substitution and freestanding membranes could introduce ferroelectricity in SrTiO 3 toward nonvolatile memory applications. However, the stable transformation from quantum paraelectric SrTiO 3 to ferroelectricity SrTiO 3 at room temperature still remains challenging. Here, we used multiple nano-engineering in (SrTiO 3 ) 0.65 /(CeO 2 ) 0.35 films to achieve an emergent room-temperature ferroelectricity. It is shown that the CeO 2 nanocolumns impose large out-of-plane strains and induce Sr/O deficiency in the SrTiO 3 matrix to form a clear tetragonal structure, which leads to an apparent room-temperature ferroelectric polarization up to 2.5 μC/cm 2 . In collaboration with density functional theory calculations, it is proposed that the compressive strains combined with elemental deficiency give rise to local redistribution of charge density and orbital order, which induce emergent tetragonality of the strained SrTiO 3 . Our work thus paves a pathway for architecting functional systems in perovskite oxides using a multiple nano-design.