Enhanced hybrid improper ferroelectricity in Sr3−xBaxSn2O7 ceramics with a Ruddlesden–Popper (R–P) structure

Hybrid improper ferroelectricity (HIF) has received increasing scientific attention since it provides great potential for realizing single phase room temperature multiferroicity with strong magnetoelectric coupling, and Ruddlesden–Popper (R–P) compounds AO(ABO3)n with even n are the most important candidates for HIFs. However, the modulation of ferroelectric polarization is recognized as a challenging issue. Here, Sr3−xBaxSn2O7 ceramics with a large remanent polarization with respect to other R–P HIFs (∼1.0 μC/cm2) combined with a reduced coercive field are reported. The polarization increases obviously with the increasing tolerance factor, inconsistent with the previous understanding. This is because the amplitude of tilt increases and rotation decreases, which results in the increased distortion of SnO6 octahedra. That is, the polarization of R–P compounds should be determined by the combined effects of tilting and rotation and not be simply evaluated by the tolerance factor.