Polarization switching dynamics and switchable diode effect in hybrid improper ferroelectric Ca₃Ti₂O₇ ceramics

Abstract

Hybrid improper ferroelectric Ca3Ti2O7 (CTO) ceramics were synthesized by a solid‐state reaction method. Their polarization switching currents, dynamic processes of polarization‐switching, and leakage current properties were investigated. It was found that the dynamic polarization curves of CTO ceramics exhibit obvious dependence on the frequency of the driving electric fields. Moreover, CTO ceramics show a switchable diode effect. The underlying mechanism for the observed effects were proposed based on the interplaying between mobile charged defects and bound charges. The charged defects also lead to a decrease in the band gap of the CTO ceramic, as revealed by absorption spectrum analysis.

The novel electrical properties in quasi‐2D hybrid improper ferroelectric Sr3Sn2O7 ceramic and the structural modulation

“…However, the peak‐current value and the coercive field decreased in I–E loops with the decrease of measuring frequency, which can be attributed to longer electric field action, enabling the likelihood of dipole switching. These trends in Sr 3 Sn 2 O 7 are similar to those observed in Ca 3 Ti 2 O 7 ceramics 23 …”

“…The trend of the hysteresis loops is influenced by the magnitude of the leakage current density value and the P r . 23 With increasing temperature, the J-E loops demonstrated an opposite trend compared to the low-temperature as seen in Figure 5A which is marked by number 1-4 to show the order of path. The hysteretic behavior also becomes less pronounced, which corresponds exactly to the decrease of the P r in Figure 4C.…”

“…A significant increase in leakage current with increasing temperature is observed. In addition, low leakage current density at RT is observed in the Sr 3 Sn 2 O 7 ceramic, which is roughly two orders of magnitude less than that of Ca 3 Ti 2 O 7 ceramics, 23,33,34 indicating that Sr 3 Sn 2 O 7 ceramic possesses exceptional insulating properties.…”

“…The J-E curves showed asymmetric characteristics on the electric field axis below 130 • C, indicating the presence of an internal bias field due to the unbalanced accumulation of charged carriers and oxygen vacancies. 23,34 Additionally, the J-E curves exhibited obvious hysteretic behavior, which can be attributed to the ferroelectric polarization switching process occurring in Sr 3 Sn 2 O 7 ceramic. Besides the ohmic conduction contribution, there exists a switching current due to polarization in the positive sweep regions from 0 to +125 kV/cm and from 0 to −125 kV/cm, which is caused by the inversion of the dipole.…”

“…These trends in Sr 3 Sn 2 O 7 are similar to those observed in Ca 3 Ti 2 O 7 ceramics. 23 Figure 2C,D shows the P-E and I-E loops using the PUND method at RT. This method can eliminate the impact of outside factors, including parasitic capacitance and current leakage.…”