Highly Tunable Ferroelectricity in Hybrid Improper Ferroelectric Sr3Sn2O7

The successful theoretical prediction and experimental demonstration of hybrid improper ferroelectricity (HIF) provides a new pathway to couple octahedral rotations, ferroelectricity, and magnetism in complex materials. To enable technological applications, an HIF with a small coercive field is desirable. Sr3Sn2O7 single crystals are successfully grown, and it is discovered that they exhibit the smallest electric coercive field at room temperature among all known HIFs. Furthermore, it is demonstated that a small external stress can repeatedly erase and re‐generate ferroelastic domains. In addition, using in‐plane piezo‐response force microscopy, abundant charged and neutral domain walls are charaterized. The observed small electrical and mechanical coercive field values are in accordance with the results of the first‐principles calculations on Sr3Sn2O7, which show low energy barriers for both 90° and 180° polarization switching compared to those in other experimentally demonstrated HIFs. The findings represent an advancement towards the possible technological implemetation of functional HIFs.