First-order phase transition and unexpected rigid rotation mode in hybrid improper ferroelectric (La, Al) co-substituted Ca3Ti2O7 ceramics

Enhanced hybrid improper ferroelectricity in Fe/Nb cosubstituted Ca3Mn2O7 ceramics

“…Curie temperatures are obtained from the DSC measurements reported previously. 12,40,43,50 The linear fitting results are depicted by red dash lines with the critical τ value [Color figure can be viewed at wileyonlinelibrary.com] there are the rather simple antiparallel 180°-type domain configurations in Ca 3 [Mn 0.5 (Fe 0.5 Nb 0.5 ) 0.5 ] 2 O 7 , and this is similar to the situation in Ca 3 Ti 2 O 7 . [43][44][45] The previous work has also demonstrated that engineering the phase transition by chemical substitution is a useful method to modulate the domain configurations in ferroelectrics.…”

“…Unfortunately, however, it remains challenging to observe the switchable polarization at room temperature, and its inferior remanent polarization (~1 μC/cm 2 for polycrystalline and ~6.4 μC/cm 2 for single-crystal Ca 3 Ti 2 O 7 ) also limits the investigation and application. 9,34,39,40 Therefore, systematic studies of Ca 3 [Mn 1x (Fe 0.5 Nb 0.5 ) x ] 2 O 7 (x = 0.15, 0.25, and 0.50) ceramics have been conducted to tune the crystallographic symmetry and ferroelectricity. The microstructures and distribution of grain size of dense Ca 3 [Mn 1x (Fe 0.5 Nb 0.5 ) x ] 2 O 7 ceramics are shown in Figure 4.…”

“…(C) Curie temperatures of n = 2 R‐P HIFs against the tolerance factors of their perovskite units. Curie temperatures are obtained from the DSC measurements reported previously 12,40,43,50 . The linear fitting results are depicted by red dash lines with the critical τ value [Color figure can be viewed at wileyonlinelibrary.com]…”

Review of experimental progress of hybrid improper ferroelectricity in layered perovskite oxides

“…The most typical example is CaTiO 3 , which has a nonpolar orthorhombic Pbnm phase. Although octahedral rotations by themselves cannot induce ferroelectricity in the simple perovskites ABO 3 , the combination of two OOR modes (a 0 a 0 c + and a − a − c 0 or a 0 a 0 c − ) has been recently predicted to trigger ferroelectricity in oxides with superlattices or layered perovskite structures [29][30][31][32][33][34][35][36][37]. This is a special improper ferroelectricity called 'HIF' because two distortions can condense at different temperatures [15].…”

Novel optical properties and induced magnetic moments in Ru-doped hybrid improper ferroelectric Ca3Ti2O7

“…While for Ca 3 Ti 1.9 Ru 0.1 O 7 , the values of  R and  T are 9.842° and 10.193°, respectively. According to the formula: P∝Q R Q T (where P is spontaneous polarization,  represents the coupling coefficient, and Q R and Q T are amplitude of rotation and tilt respectively)[25]. The angle of tilt mode increased after Ru doping, so the spontaneous polarization may be improved in Ca 3 Ti 1.9 Ru 0.1 O 7 .…”