The Impact Of The High The Density Pzt95 / 5 Ceramics Phase Transition And Discharge Properties Of,

The polarized PZT 95/5 ferroelectric ceramics with a rhombohedral structure (F_R) will transform into the antiferroelectric phase with an orthorhombic structure(A_O) when subjecting to proper shock loadings. This Phase transition will result in a rapidly depolarizing process, in which the dramatic releasing of the surface charges bounded in the ceramics happens. This kind of ceramics has been successfully used in the United States, United Kingdoms and Russia as the promising pulsed power supplies to provide large amplitude current. Studies of the phase transition mechanism and electric current generation behavior are of essential importance for exploiting and developing applications of the materials. Furthermore, the accurate identify of the F_R to A_O phase transition is also a challenge to the experimental researchers, both in method and diagnosis techniques, for it occurs below the Hugoniot elastic limits of the ceramics and the phase transition process would be seriously affected by its constitutive behavior, and the construction of the constitutive relations in the elastic stress region involving phase transition is not yet an easy job.In this paper, the domestic PZT 95/5 ceramic with a density of 7.76g/cm³ was chosen as our test sample and the one-stage gas gun at LSD was used as the planar shock-loading tools to create the one-dimensional strain states in the ceramics. Based on the measured Hugoniot data, the sound velocities at the Hugoniot states and the depoling current profiles determined from the experiments, a constitutive model involving the irreversible phase transition in the elastic stress region was proposed; behavior of the phase transition related with the shock loading stresses and the shock-depoling properties was carefully analyzed. Main results are as follows:1. The axial stress(σ) to particle velocity(u) relation, i.e. the Hugoniot of the polarized high density PZT 95/5 ceramics at stresses ranging from 0.48 GPa to 3.78 GPa, were measured via reverse-impact experiments, by using the VISAR instrumentation techniques coupled with a fused quartz window. The elasticσ-u Hugoniot of the polarized ceramics behaves totally different from that of the un-polarized ones in that the former can be characterized by a three-sections broken-line while the latter is linear. These results provided a basis for establishing a constitutive relation involving the phase transition in the elastic stress regions. In reference to the dynamic yielding threshold stress data for low density PZT 95/5 ceramics by Setchell et al and to the crystal lattice parameter changes before and after the phase transition by Avdeev et al, it is concluded that the phase transformation of domestic high density PZT 95/5 is a first order phase transition occurring in the stress region, roughly from about 0.5 GPa to about 2.0 GPa.2. Sound velocities were calculated from the particle velocity profile of PZT 95/5 ceramic, which is obtained from the reverse-impact experiments. Result shows that the longitudinal sound velocity increase with shock stress, it can also be expressed by a three-sections broken line. It is the phase transition that results in the inflections in the slopes of the sound velocity versus stress curve.3. Shock-induced depoling process and electric current releasing of the high density PZT 95/5 ceramics were studied. Firstly, the current-releasing behavior in the phase transition stress region was studied by comparing the released polarization (P_rs) under shock compression and the initial remanent polarization (P_r). Results show that the magnitude of the current released increases with the shock stress. Analysis of the current data further confirms that the phase transition should start at stress about 0.30±0.15 GPa and almost complete at 1.90±0.15 GPa. Secondly, the influence of the circuit loads on the output currents at stresses where phase transition completes was discussed. Analyses of the equivalent circuit and the experiment results show that the current magnitude will keep constant when phase transition has completed. The current in circuit will only be influenced by RLC loads such that: the inductance loads will induce a rising current magnitude and a oscillatory profile, the pure resistance loads will induce a stable current output and the response time will increase with the resistance magnitude.4. By using the experiment data of the Hugoniot, the sound velocity ,and the elastic modulus at ambient conditions for the high density PZT 95/5 ceramics, and by expanding Tang Zhiping's irreversible phase transition model for 1-D stress loading conditions to 1 -D strain conditions of this study, a new constitutive model for F_R→A_O phase transition of the high density PZT 95/5 ceramics was proposed: whereσ_A andε_A are threshold stress and strain, andσ_B andε_B are ending stress and strain of the phase transition, respectively. All of them were determined from F_R→A_O phase transition experiment:σ_A=0.23 GPa,ε_A=1.48×10^-3,σ_B=1.94 GPa,ε_B=1.34×10^-2.5. Based on the experimentally measured electric charges released during the phase transition, a volume fraction function,ξof the A_O phase due to the phase transition is introduced to describe the dynamic phase transition behavior by definition, the volume fraction fuctionξcan be expressed as the ratio of the released polarization P_rs to the remanent polarization P_r Since the density of the F_r phase and A_O phase have been precisely determined, the mass fraction change of the A_O phase due to the phase transition can easily be calculated from the volume fractionξ. By combination of theσ-u Hugoniot and the measured electric charges released, the volume fraction parameterξcan further be expressed as the function of the shock stress (σ) such that:This also implies that the phase transition of the polarized high density PZT 95/5 ceramics initiates at stress of 0.23 GPa and completes at 1.94 GPa.In conclusion, a method for studying experimentally the constitutive relations under 1-D strain condition and a model for describing the dynamic phase transition behavior of the domestic high density PZT 95/5 ceramics have been developed. The method mainly includes two basic experimental techniques-the reverse impact techniques and the VISAR instrumentation techniques coupled with a transparent window, to obtain the particle velocity profile at the sample-window interface and the sound velocity profile of the sample under shock loadings. These methods should be applicable to other materials for constitutive measurement and phase transition study. The authors believe that the shock dynamic parameters and the characteristics of the shock-induced phase transition of the domestic high density PZT 95/5 ceramics obtained in this study would be of practical importance in open up its new applications.