Toughening Piezoelectric Ceramics

A novel approach was proposed and developed for toughening piezoelectric ceramics without degrading their piezoelectric properties, where the coarse particles were incorporated and dispersed into the fine-grained matrix to prepare complex microstructure. Effects of the present approach were determined in PZT, BaTiOs and (Bii/2Nai/2)Ti03 ceramics, and the mechanism of the toughening effects of such abnormal microstructure was discussed.With incorporating coarse particles into PZT matrix, the grain size distribution was broadened without change of the intergranular fracture mode, and the fracture toughness was significantly enhanced and reached the maximum KIC of 1.43MPa-m1/2, while that of the matrix was 1.07MPa-mI/2. The coarse grain debonding played as the primary toughening mechanism. Meanwhile, the dielectric constant ET33/s0 slightly increased and piezoelectric properties showed slight variation in the present modified PZT piezoelectric ceramics.In BaTiO3 ceramics, the grain size distribution was widened and the toughness was improved distinctly by incorporating coarse BaTiOs particles and obtained the maximum K\c of 1.97MPa-mI/2, while that of the matrix was 1.14MPa-m1/2. The coarse grain microcracking was the main toughening mechanism. The piezoelectric properties varied slightly in comparison to the reference BaTiOs ceramics.In (Bii/2Nai/2)Ti03 ceramics, the toughness and piezoelectric properties showed obvious grain size dependence. The toughness, electromechanical coefficient kp, mechanical quality factor Qm, capacitivity eT33/s0 and dissipation tan5 were increased, and frequency constant Np was depressed with increasing grain size, while the effects of porosity were contrary. The grain size distribution was extended distinctly and the toughness was significantly improved by incorporating coarse particles and KIC achieved the maximum of 1.91MPa-m . The coarse grain microcracking was the primary toughening mechanism. The piezoelectric properties showed slight variation incomparison to the reference ceramics.An interesting phenomena in these ceramics was discovered that the toughness of the ceramics with abnormal microstructure showed higher KIQ than that of the ceramics with normal microstructure when their average grain sizes were equal. This interesting phenomenon was analyzed by varying toughening mechanism models, and the theoretic data coincided with the experimental values, which proved the crack resistance in the ceramics with abnormal microstructure was more than that with normal microstructure.