Effects of dc electric field on mechanical properties of piezoelectric ceramics

The effects of dc electric field on mechanical properties such as hardness, fracture toughness, flexural strength and flexural fatigue strength of piezoelectric ceramics were investigated. Hardness and fracture toughness were not influenced by the dc electric field, where as the flexural strength and the fatigue strength degraded with the absolute value of the electric field. The degradation of the flexural strength and the acceleration of fatigue were greater under an electric field whose direction was opposite to the poling direction than an electric field whose direction was the same as the poling direction. The main cause of strength degradation and fatigue acceleration in piezoelectric ceramics is estimated to be the microscopic internal stress which is generated at the grain boundary by the piezoelectric and domain switching deformations.