Hybrid improper ferroelectricity and phase transition in La2Sr(Sc1− <i>x</i> In <i>x</i> )2O7 ceramics

Oxygen octahedral rotation is essential for hybrid improper ferroelectrics (HIFs), but interlayer rumpling will compete with oxygen octahedron rotation, leading to the suppression of ferroelectricity in layered perovskite materials containing trivalent cations at the B-site. In the present work, single-phase dense La2Sr(Sc1−xInx)2O7 ceramics with double-layered Ruddlesden–Popper structures have been prepared, and the presence of room-temperature HIF is evidenced by the ferroelectric hysteresis loops. The polar A21am phase is adopted at room temperature, and it will transform into a nonpolar Amam phase above the Curie temperature. The Curie temperature increases linearly with the content of In3+ cation and with decreasing tolerance factor, whereas the ferroelectric polarization decreases with the substitution of In3+ cation at the B-site owing to the suppression of oxygen octahedral rotation. The present work demonstrates the room-temperature HIF in La2Sr(Sc1–xInx)2O7 ceramics and emphasizes the essential role of tolerance factor in determining the Curie temperature.