Large anisotropy of fracture toughness in mechanically poled/depoled ferroelectric ceramics

We observed large anisotropy of indentation fracture toughness in both mechanically poled and depoled lead titanate zirconate (PZT) ceramics under uniaxial compression up to 400 MPa. The fracture toughness anisotropy can reach as much as 3.82 in the former and 3.63 in the latter, which are both considerably larger than that of 2.62 in electrically poled PZT ceramics. This phenomenon is thought to be caused by ferroelastic domain switching during indentation and by the existence of more saturated domain orientation textures under compression than under electrical poling.