Thermopiezoelectric Response Of Ferroelectric Thin Film Due To Pulsed Laser Irradiation

Current interest in ferroelectric thin film results from the numerous potential applications in micro electronics, micro electromechanical system (MEMS) and information storing that utilize the unique ferroelectric, dielectric, pyroelectric, electro-optic, acousto-optic, and piezoelectric properties of the material. Therefore, the preparation and properties studies on the ferroelectric thin film have attracted great attention. It is well known that the ferroelectric thin films operating in many structural components, especially aerospace component, are ineluctably subjected to severe thermal loading which may be produced by aerodynamic heating, by laser irradiation, or by localized intense fire. A significant amount of energy is delivered to a thin film surface in short time, which fleetly heats the film to elevated temperature and thermal stress levels. The structural components may lead to failure due to the temperature of thin film exceeding the courier temperature or stress concentration. For studying the failure characteristic of ferroelectric thin film under dynamic thermal loading, the thermopiezoelectric fields must be firstly obtained. Thus, the study on the thermopiezoelectric response of ferroelectric thin film due to pulsed laser irradiation in ferroelectric thin film, which is significant for the life prediction and failure mechanism of a piezoelectric thin film system subjected to dynamic thermal loading.In this paper, the thermopiezoelectric responses of the Pb(Zr0.52Ti0.48)O3 (PZT) and Bi3.15Nd0.85Ti3O12 (BNT) ferroelectric thin films induced by pulsed laser are studied by analytic and numerical simulative methods. The analytic result is compared with that of the numerical simulation. The main contents are given as follow1. A cylindrical model is established. Based on heat conductivity equations, constitutive relations and boundary conditions, the analytic solutions of thermopiezoelectric fields of the ferroelectric thin films system induced by dynamic thermal loading are obtained by piezoelectric potential function method and the analytic solutions are calculated by MATLAB. To validate the results solved by piezoelectric potential function method, the thermopiezoelectric fields of the ferroelectric thin films system induced by pulsed laser are simulated by finite element method too.2. Parameter preparation. For calculating the thermopiezoelectric fields of PZT and BNT, the material parameters of them must be obtained. Firstly, the material parameters of PZT are obtained by reference. Secondly, the Mechanical parameters of BNT are approximate by Bi4Ti4O12. Finally, BNT powder is prepared by metal organic decomposition(MOD) method. The specific heat and thermal conductivity of BNT material are measured by Modulated Temperature Diferential Scanning Calorimetry(MTDSC). 3. The thermopiezoelectric fields of PZT and BNT thin films induced by pulsed laser are obtained by MATLAB numerical calculation and finite element method simulation. The results of two methods are in good agreement. The temperature fields of PZT due to the pulsed laser irradiation are primarily controlled by the radial intensity distribution and temporal intensity distribution of the pulsed laser. The displacement along the radial direction is much larger than that along the vertical direction, and the radial electric displacement is much larger than vertical electric displacement. The normal and shear stresses in region irradiated by the laser beam are much larger than that outside the region, and all of the radial, circumferential and vertical stresses are compressive in the irradiated region. Furthermore, the values of radial and circumferential stresses are much larger than that of the vertical and shear stresses. Propagation of interfacial crack induced by delamination is possibly due to the compressive radial and circumferential stresses in laser beam the irradiated region. In the same condition, the thermopiezoelectric field distribution of BNT thin film is similar to that of PZT. The temperature of BNT thin film is lower than that in PZT thin film. The value of stress in BNT thin film is larger than that in PZT thin film. Comparing with the PZT thin film, there are larger displacement and smaller electric field in BNT thin film. These results provided a theoretical direction for the life prediction and failure mechanism of a piezoelectric thin film system subjected to dynamic thermal loading.