The Electro-mechanical Properties Of PZT, PVDF Ferroelectric Materials In Novel Bulge Test

Piezoelectric and ferroelectric materials have been widely applied in defense, electronics, industrial and other fields, which have a significant influence on the development of new high-technology industry. The analysis of parameters measurements and possible failure mechanisms of ferroelectric materials are crucial to reveal their application and reliabilities. In this work, a modified bulge test model was developed to measure the elastic stiffness coefficient, piezoelectric coefficient and elastic modulus of ferroelectric materials under the coupled condition of mechanical and electrical loads. An improved bulge test system was designed to measure those properties of PZT-4 piezoelectric ceramic, PZT and PVDF thin film. The characteristics of electric hysteresis loop of ferroelectric materials were analyzed under different mechanical and electrical loads. The variation of residual polarization, coercive field and saturation polarization were discussed. The main contents can be summarized as follows,Firstly, on the basis of the traditional bulge principle, a constitutive model of bulge test was proposed to describe the properties of ferroelectric materials. The elastic stiffness constant and piezoelectric coefficient of ferroelectric ceramics can be estimated by using the experimental data. This model can be extended to measure other properties of new ferroelectric materials and ferroelectric composite materials under the coupled effect of mechanical and electrical loads. An analytical method was presented to discuss the mechanical and electrical features of new ferroelectric materials.Secondly, the properties of commercial PZT-4 piezoelectric ceramic under the effect of mechanic and electricity were analyzed with the aid of the improved bulge test model. The elastic stiffness coefficient of PZT-4 piezoelectric ceramic was obtained according to the pressure-deflection curve under different electric field intensity and the bulge test model, c13=12.56×1010 N/m2. The results show that the elastic stiffness coefficient decreases with the increasing of applied voltage. The electric hysteresis loops under different applied voltages were measured. The results show that the electric hysteresis loops become flat with the increasing of applied voltage, while the value of coercive field increase, the residual polarization and the largest polarization decrease. The elastic modulus and residual stress are obtained respectively, E=72.27 GPa and σr=51.72 MPa.Thirdly, the electro-mechanical coupling properties of PZT ferroelectric thin films were measured by the aid of the improved bulge test system. The electric hysteresis loop of PZT thin films under different pressure was measured. The results show that the residual polarization decrease with the increasing of applied voltage, but the value of coercive field increase. The pressure-deflection curve of PZT thin films under different electric field intensity was measured, then the variation of elastic modulus with the change of applied voltage was obtained. The experimental results show that the elastic modulus of PZT thin films ranges from 3.29 GPa to 5.02 GPa while applied voltage increases from 0 to 14 V.Fourthly, the electro-mechanical coupling properties of poly vinylidene fluoride(PVDF) polymer ferroelectric polymer thin films were gained by the aid of the improved bulge test system. First, the pressure-deflection curve of PVDF thin films under different pressure was tested, then we obtained the average value of elasticity modulus, about 1.93 GPa. The pressure-deflection curve of PVDF thin films at different voltages was tested, and the power electric response behavior of PVDF organic thin film was analyzed. The elastic stiffness constant of PVDF ferroelectric polymer film was calculated,c12=1.02×10~9N/m2. Then we obtained the relationship of piezoelectric constant and the applied voltages. The results show that, the piezoelectric constant reduced from –0.466 C/m2 to –0.013 C/m2, when the applied voltages arranged from 20 V to 150 V. This result indicates that, the applied voltage and biaxial tensile stress have an important effect on the piezoelectric property of ferroelectric polymer film.