Hybrid improper ferroelectricity and enhanced Curie temperature in co-substituted La2SrSc2O7-based ceramics

Hybrid improper ferroelectrics (HIFs) have attracted considerable attention owing to their potential to realize single-phase multiferroic materials with intrinsic electric field-controlled magnetism. In this work, dense single-phase La2Sr1−xCaxSc2−xGaxO7 (0.00 ≤ x ≤ 0.20) ceramics with double-layered Ruddlesden–Popper structures were synthesized by a simultaneous co-substitution strategy. The remanent polarization of the ceramics decreases monotonically with increasing x, which is microscopically governed by the suppressed amplitude of the oxygen octahedral rotation mode and the diminished disorder of A-site cations. The ferroelectric-paraelectric phase transitions are revealed by the temperature-dependent dielectric response. A clear linear correlation between the Curie temperature and the tolerance factor has been found for the La2Sr1−xCaxSc2−xGaxO7 (0.00 ≤ x ≤ 0.20) ceramics, thereby validating the classification scheme of HIFs. This work clarifies the influence of co-substitution on oxygen octahedral distortions and A-site cation disorder in La2SrSc2O7-based ceramics, providing an effective strategy for tuning the Curie temperatures of HIFs.