The Charge-free Zone Model for Conductive Cracks in Dielectric and Peizoelectric Ceramics

In the charge-free zone (CFZ) model, dielectric and piezoelectric ceramics are treated to be mechanically brittle and electrically ductile. For an electrically conductive crack under electrical and/or mechanical loading, various charge emission mechanisms may function jointly at the tip due to the high electric field concentration. Charge emission and charge trapping consume more work and thus lead to a high value of the electric toughness. The failure criterions derived from the CFZ model were verified by experimental results on poled and thermally depoled lead zirconate titanate ceramics.