Near tip stress intensity factor of an edge surface crack in PZT thin films with 90° domain switching

摘要

Ferroelectric thin films, such as lead zirconate titanate Pb(Zr_xTi_(1-x))O_3 (PZT) thin films, have been extensively applied over the last decades to high-value capacitors, infrared detectors, sensors, actuators, optical switches, ferroelectric field-effect transistors and non-volatile memories [1,2]. The ferroelectric thin films operating in many structural components, especially aerospace components, are ineluctably subjected to severe thermal loading which may be produced by aerodynamic heating, laser irradiation or localized intense fire [3]. Thermopiezoelectric response of PZT thin films was studied using the piezoelectric potential function method [4]. However, it is natural that ferroelectric thin films may fail due to thermal, mechanical, and electric loading. Fracture mechanics analyses of bulk ferroelectric materials under coupled mechanical and electrical loadings were studied extensively in the past several years [5,6]. Because of the particular electromechanical coupling effect, the fracture mechanism received high attention for bulk ferroelectric materials with defects such as cracks, impurities and holes [7,8]. When a ferroelectric material with cracks is subjected to external loadings, domain switching may occur [9]. Under the coupling of mechanical and electric loadings, domain switching could toughen poled ferroelectric ceramics with an impermeable crack [10]. The domain switching zone around the crack-tip causes the nonlinear stress-strain behavior and shields the crack-tip from the external loadings [9,11]. For bulk ferroelectric materials the shielding stress intensity factor (SIF) due to domain switching was usually evaluated based on the weight function method [7]. However, for a film/substrate system the SIF was obtained by the weight function method for one-dimensional edge cracks in a semi-infinite body [12]. Because of their inherent complexity, relatively few solutions for the failure mechanism of ferroelectric thin films under an external loading are available in the literature.