Core–Shell Formation by Diffusion Along Grain Boundaries in Lead‐Free Ferroelectric Ceramics

ABSTRACT The search for lead‐free ferroelectrics, driven by environmental concerns, has continued for decades, yet no material has fully replaced PbZrTiO 3 ‐based compositions. Introducing core–shell architectures offers a promising route to enhance functional properties; however, their realization in lead‐free systems remains limited. In this work, we present a novel method for obtaining core–shell structures in fully sintered lead‐free ferroelectric ceramics by thermally treating two ceramic plates in direct contact—hereafter referred to as the contact method. This approach enabled core–shell formation in BaTiO 3 , SrTiO 3 , and Na 0 . 5 Bi 0 . 5 TiO 3 systems through interfacial diffusion. Bi over‐stoichiometry in NBT strongly promoted shell formation and enhanced interdiffusion, yielding high chemical contrast with diffusion depths exceeding 300 µm. Furthermore, a fully developed core–shell architecture in BaTiO 3 was obtained, resulting in a significant improvement in resistivity. These findings demonstrate the potential of the contact method as a simple and versatile route for tailoring the microstructure and functional properties of lead‐free ferroelectric ceramics.