PZT陶瓷本构行为与断裂性能的相关性研究

Correlation between Constitutive Behavior and Fracture Performance of PZT Ceramics

铁电陶瓷的力学性能直接决定了其加工性能和铁电器件的可靠性。目前,无论是实验还是理论报道的压电陶瓷材料的断裂韧性都与30年前的报道接近,限制了压电器件在高可靠性要求的情况下的应用。本研究试图揭示可用于优化铁电陶瓷断裂性能的参数。利用单轴压缩方法、裂纹尖端张开位移(Crack-tip opening displacement,COD)技术和单边V型缺口梁(Single-side V-notch beam,SEVNB)技术分别测定三种典型PZT陶瓷的应力-应变曲线、本征断裂韧性和长裂纹断裂韧性。结果表明,本征断裂韧性与材料的杨氏模量正相关,说明提高铁电体的杨氏模量是提高其本征韧性的有效途径。长裂纹断裂韧性与本征韧性和非本征铁弹性畴变/相变增韧有关,说明优化铁电陶瓷的铁弹翻转行为可以改善其非本征效应。软掺杂PZT相较于硬掺杂PZT具有较低的矫顽应力和较高的残余应变,呈现较强的铁弹性翻转和较高的屏蔽韧性;在不同PZT材料中观察到的断裂模式也被认为与材料不同的铁弹性翻转行为有关,软PZT陶瓷呈现沿晶断裂,铁弹性翻转较弱的硬PZT呈现穿晶断裂。综上所述,优化铁电材料的杨氏模量和铁弹翻转行为有望提升其断裂韧性。

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.