中文摘要：

用正交偏振光显微镜,通过原位观察研究了恒位移下BaTiO3单晶贯穿裂纹快速扩展与畴变的关系,以及在室温空气中（湿度为35%RH）亚临界裂纹扩展和畴变的关系。结果显示,加载开始时首先出现畴变,且其体积分数随载荷升高而增大;当载荷达到临界值时,裂纹快速形核、扩展并止裂,在空气中保持恒位移,畴变能慢慢发生,即空气中水吸附能促进畴变,当畴变发展到临界条件时就引起裂纹的亚临界扩展（即应力腐蚀）。

英文摘要：

BaTiO3 single crystal with superior dielectric,pyroelectric,piezoelectric and electrooptic properties has triggered much attention due to numerous potential applications in microelectronic devices,sensors and micro/nanoelectromechanical systems.However,one of the main disadvantages for BaTiO3 single crystal is that after long-term working under mechanical field or electric field,cracks may be nucleated and propagated.The crack nucleation and propagation in ferroelectric materials are closely related to the domain configurations,and their relationship with crack propagation,nucleation and domain switching,is not known clearly,so it is imperative to take more effort to research this relationship.Here,the relationship of domain switching with crack propagating quickly as well as sub-critical crack growth in ambient air for constant deflection sample of BaTiO3 single crystal has been in situ studied using a polarized light microscopy.The results indicate that domain switching occurs first and the volume fraction of switched bands increases during loading.When the load reaches to a critical value,crack will be initiated and propagated quickly.Keeping the constant deflection, the domain switch could still occur but very slowly,i.e.,adsorption of water in air is able to promote domain switching.As a result of adsorption enhanced domain switching,cracks are propagated slowly in air,that is say,sub-critical crack growth or stress corrosion cracking in air could occur for BaTiO3 single crystal under constant deflection.