Record‐Low Coercive Field and Stable Curie Temperature in Bulk Hybrid Improper Ferroelectrics via Synergistic A / B ‐Site Co‐Substitution
Zhe Guo, Jia Ling Li, Jia Min Lin, Tu Lai Sun, Yu Hui Huang, Xiao Li Zhu, Xiao Qiang Liu, Xiang Ming ChenABSTRACT
Hybrid improper ferroelectrics (HIFs) have attracted increasing scientific attention due to their unique coupling between structural distortion and polarization, offering a highly promising platform for ferroelectrics and single‐phase multiferroics with intrinsic electric field‐controlled magnetism. While, the intrinsically high coercive fields ( E c ) have been remained as a big issue. In the present work, we demonstrate a synergistic A / B ‐site co‐substitution strategy in La 2 Sr 1‐ x Ca x (Sc 1‐ x Fe x ) 2 O 7 ceramics to reshape the ferroelectric energy landscape. Consequently, room‐temperature ferroelectricity with a remarkably reduced E c to approximately 6 kV/cm, a record low value for bulk HIFs, was achieved in La 2 Sr 0.7 Ca 0.3 (Sc 0.7 Fe 0.3 ) 2 O 7 ceramics. This reduction is primarily attributed to a significant structural evolution within the ferroelectric domains, specifically the A ‐site cation disorder induced by co‐substitution triggers a distinct transition from coarse stripe domains to refined stripe nanodomains. Moreover, the correlation between Curie temperature and tolerance factor of La 2 Sr 1‐ x Ca x (Sc 1‐ x Fe x ) 2 O 7 breaks the linear relationship previously established in A ‐site cation‐disordered La 2 SrSc 2 O 7 , demonstrating that the co‐substitution of Ca 2+ and Fe 3+ cations plays a significant role in thermodynamically stabilizing the ferroelectric phase. Furthermore, A weak short‐range magnetic order is observed in La 2 Sr 0.7 Ca 0.3 (Sc 0.7 Fe 0.3 ) 2 O 7 ceramics. This work highlights the importance of A / B ‐site co‐substitution in designing novel HIFs and discovering single‐phase multiferroic materials.