Insights into deformation and fracture mechanisms of CaBi ₄ Ti ₄ O ₁₅ piezoceramics via doping and poling engineering

Abstract Mechanical behaviors are specifically important considerations for piezoelectric materials in practical applications. As promising high‐temperature piezoelectric materials, CaBi 4 Ti 4 O 15 (CBT) ceramics have been studied for many years, and significant progress has been made in enhancing their electrical performance. However, the mechanical properties of CBT ceramics have received scant attention from researchers to date. In this study, the hardness and fracture toughness of Nb/Mn co‐doped CBT ceramics were systematically examined. The effects of ion doping and electric poling on plastic deformation and crack propagation, as well as fracture behaviors, were revealed in detail. The results demonstrate that numerous layered ferroelectric domains with nanoscale dimensions are observed on the surface of plate‐like grains, and the corresponding domain boundaries are further confirmed as 180°‐like domain walls by high‐resolution transmission electron microscopy (HRTEM). Nanoindentation and Vickers indentation tests reveal that the Nb/Mn co‐doped CBT ceramics with smaller grain size and higher density possess greater hardness and higher resistance to deformation. The poling process tends to decrease hardness due to the presence of micro‐defects and stress concentration after domain rearrangement under applied electric field. Yet, the crack propagation along the poling direction is retarded by ferroelastic deformation around the crack tip, exhibiting significant fracture toughening. R ‐curve analysis further elaborates on intrinsic and extrinsic toughening behaviors and indicate that ceramics with higher doping levels possess enhanced toughening behaviors and improved fracture resistance. This work not only deepens our understanding of the mechanical behaviors of CBT piezoelectric ceramics, but also offers valuable guidance for the design and development of high‐performance piezoelectric materials for practical applications.