Correlation between Constitutive Behavior and Fracture Performance of PZT Ceramics

The fracture properties of ferroelectrics directly determine their processability and reliability of devices made of them.However, both experimentally and theoretically reported fracture toughness of piezoelectric ceramic materials remains nearly the same as that reported 30 years ago, limiting the application of piezoelectric devices in situation where high reliability is required.Here, we try to reveal the parameters that could be used to optimize the fracture performance of ferroelectrics.Specifically, stress-strain curves, intrinsic fracture toughness and long-crack fracture toughness of three typical PZT ceramics were measured by uniaxial compression method, crack-tip opening displacement (COD) technique and single-side V-notch beam (SEVNB) technique, respectively.It is shown that the intrinsic fracture toughness is positively correlated with the Young's modulus of the material, which suggests that improving the Young's modulus of ferroelectrics is an effective way to improve their intrinsic fracture toughness.The long-crack fracture toughness is related to the intrinsic toughness and extrinsic ferroelastic domain switching/phase transformation toughening, which also suggests that optimizing the ferroelastic switching behavior of piezoelectric ceramics can improve their extrinsic effect.Compared to the hard doped PZT, the soft doped PZT has low coercive stress, high remanent strain and high shielding toughness.The fracture patterns observed in different PZT materials are related to the different ferroelastic switching behavior of the materials.Soft PZT ceramics exhibit intergranular fracture, while hard PZT with weak ferroelastic switching behavior exhibits transgranular fracture.In conclusion, fracture toughness of ferroelectrics is enhanced by optimizing Young's modulus and toughening of ferroelastic switching. Key words: