Hybrid Improper Ferroelectricity in Highly Cleavable Single Crystals of Dion‐Jacobson‐Compound CsBiNb2O7

Abstract Dion‐Jacobson compound CsBiNb 2 O 7 exhibits supposedly hybrid improper ferroelectricity (HIF), resulting from two different structural distortions. The highly‐cleavable single crystal of CsBiNb 2 O 7 has been successfully grown and found large ferroelectric polarization as large as 30 μC cm ‐2 with the coercivity of 310 kV cm ‐1 from polarization‐electric field measurements on the crystals. Using piezoelectric force microscopy, a systematic study is on the ferroelectric domain structure and dynamics of CsBiNb 2 O 7 , unveiling the rich nature of its domain/domain wall evolution upon poling. The record large switchable polarization in CsBiNb 2 O 7 among HIF compounds brings HIF closer to the real Pb‐free ferroelectric applications and the high cleavability of CsBiNb 2 O 7 crystals provides a unique opportunity to explore ultrathin ferroelectrics with in‐plane polarization.