Ferroelectric anomaly of perovskite layer structured Pb 2+ ‐doped Sr 2 Nb 2 O 7 ceramics

The spontaneous polarization of perovskite layer structured Sr 2 Nb 2 O 7 ferroelectrics (FEs) is originated from mainly the oxygen octahedral rotations and partially the displacement of Sr 2+ ions. However, there is FE anomaly of showing the typical characteristics of antiferroelectric (AFE)‐like behavior with double polarization–electric field hysteresis loops of Sr 2 Nb 2 O 7 ceramics by Pb doping. Here, combinations of low frequency and sub‐terahertz band dielectric measurements under applied DC field reveal field‐induced transition from AFE to FE structure. Temperature dependence of dielectric constant suggested a second‐order phase transition near 215°C, which further supported by the lattice parameters and thermal expansion coefficient extracted from the variable temperature X‐ray diffraction in the heating and cooling processes. The selected area electron diffraction results show no new superlattice spots are observed along [1 0 0] zone axis related to c direction. We proposed a model based on octahedral tilting/rotation that accounted for the incommensurate lattice modulation in the c direction for Sr 2 Nb 2 O 7 system by Pb doping. All the results show AFE‐like behavior be likely to origin from the electron structures of Pb 2+ with a 6 s 2 lone pair. Our results gave us a new concept provide possibilities for the design of AFE‐like materials in layer structured compounds with super high FE Curie point.