Textural and crystallographic phase dependencies of functional properties in BST–BCT lead-free ferroelectric ceramics featuring polymorphic phase boundary

Abstract Here, we report on the dependence of the functional properties on the textural and crystallographic phases of A- and B-site codoped BaTiO 3 ceramics, (0.82)BaTi 0.88 Sn 0.12 O 3 -(0.18)Ba 0.7 Ca 0.3 TiO 3 [BST-18BCT], featuring polymorphic phase boundaries (PPB), by varying the sintering temperature (from 1350 ∘ C to 1550 ∘ C). Increasing sintering temperatures nonmonotonically increases the grain size, as confirmed by scanning electron microscopy, whereas reducing sintering temperatures enhances tetragonality, as revealed by Rietveld refinement and corroborated by high-resolution transmission electron microscopy and selected area electron diffraction analyses. Notably, raising the sintering temperature led to a significant enhancement in remanent polarization ( P r ), saturation polarization ( P s ), and permittivity ( ε ′ ) while reducing the coercive field ( E c ). In particular, the sample sintered at the lowest temperature (1350 ∘ C) exhibited a nearly three-time increase in E c and the lowest dielectric loss (tan δ ). This study highlights that sintering temperature plays a pivotal role in tailoring the ferroelectric properties of PPB compositions by influencing the grain size, grain boundaries, and crystallographic parameters.