Improved hybrid improper ferroelectricity in B-site substituted Ca_3Ti_2O_7 ceramics with a Ruddlesden-Popper structure

摘要

Ca_3Ti_2O_7 with a Ruddlesden-Popper structure has received great scientific attention due to its high ferroelectric polarization. However, the optimization of hybrid improper ferroelectricity is still a challenging issue. In the present work, the remarkably improved ferroelectric polarization has been achieved in B-site co-substituted Ca_3Ti_(1.8)Al_(0.1)Nb_(0.1)O_7 ceramic. The improved ferroelectric polarization in this ceramic stems from the higher ferroelectric activity of Nb~(5+) cations and a larger amplitude of oxygen octahedral distortion. Moreover, the more saturated electric hysteresis loops together with the higher ferroelectric polarization can be achieved under a higher electric field and at a lower frequency. The first-order phase transition nature is proved by the thermal hysteresis, while the Curie temperature is directly proportioned to the tolerance factor. The present work provides an effective way to improve the ferroelectric properties without declining the Curie temperature in Ca_3Ti_2O_7-based hybrid improper ferroelectricities.