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

Here, we report on the dependence of the functional properties on the textural and crystallographic phases of A- and B-site codoped BaTiO₃ ceramics, (0.82)BaTi_0.88Sn_0.12O₃-(0.18)Ba_0.7Ca_0.3TiO₃ [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 (tanδ). 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.