By making use of the fact that domain-wall motions do not produce volumetric changes, an experimental method is introduced to directly and quantitatively determine the domain-wall and intrinsic contributions to the piezoelectric and dielectric responses of a ferroelectric material. Utilizing this method, the contributions from the domain walls and intrinsic part as well as their temperature dependence for lead zirconate-titanate (PZT) 52/48 and PZT-500 ceramics are evaluated. The data show that at temperatures below 300 K, the large change in the dielectric and piezoelectric constants with temperature is due to the change in the domain-wall activities in the materials. The results confirm that most of the dielectric and piezoelectric responses at room temperature for the materials studied is from the domain-wall contributions. The data also indicate that in PZT-500, both 180° wall and non-180° walls are possibly active under a weak external driving field.
In this paper, the results of a recent investigation of the dependence of the induced piezoelectric activity on temperature, electric bias field, and frequency and the electrostrictive response in the relaxor ferroelectric lead magnesium niobate-lead titanate ceramics ( (1- x)(Pb(Mg1/3Nb2/3)O3)- x(PbTiO3)) at compositions below 30% PT are presented. It was observed that the electrostrictive strain at temperatures near the dielectric constant maximum T max increases monotonically with increased PT content. For PMN:PT at compositions near 30% PT, the electrostrictive strain under a 10 kV/cm electric field can reach about 0.15% with very little hysteresis. An exceptionally large piezoelectric response with an effective piezoelectric d 33 coefficient in the electric field induced state of over 1,800 pC/N could be achieved for selected PMN:PT compositions and electric bias fields.
The electromechanical and dielectric responses of ferroelectric materials near paraelectric–ferroelectric (PF) phase transitions are examined both experimentally and theoretically. It is shown that the type of PF transition, i.e., first order and continuous transitions, and diffused phase transition found in relaxor ferroelectrics, has marked effect on the electromechanical and dielectric response behavior for materials under electric field bias. It is demonstrated that an exceptionally large piezoelectric and electromechanical response can be achieved in materials with a first order PF transition. For example, in Ba1−xSrxTiO3 (x∼0.35) ceramics at room temperature, a piezoelectric d33 larger than 1500 pm/V with very little frequency dispersion can be obtained.
Submicron grain sized PZT-SA ceramics have been produced with properties comparable to conventional coarse grained material.The degradation in dielectric and piezoelectric properties with decreasing grain size was compensated with a new dopant strategy. This made the materials piezoelectrically softer compensating for reductions in poling efficiency. The submicron grain sized materia1 has been shown to be superior to coarse grained ceramic during fine scale dicing operations.
The dielectric and piezoelectric properties of polycrystalline ceramics of relaxor ferroelectric lead magnesium niobate-lead titanate modified with La2O3, (l-x)(Pbo.~5Lao.oi~o.o05(Mgi/3N b2/3)-(x)PbTi03, h a v e been investigated. The compositional range of 0.2 5 x 5 0.4, being near the morphotropic phase boundary, was characterize d.Lanthanum doping resulted in reduction of grain size, enhanced density, and shifted t h e dielectric maximum t e m p e r a t u r e downwardly.The final microstructures of all compositions were fine ( 5 1km) with uniform grain size distributions. Room t e m p e r a t u r e dielectric constants K s of 5,000 and piezoelectric constants d33(s) of 500 pC/N were found for compositions near the morphotropic phase boundary (x = 0.33).Based on this investigation, La doped PMN-PT compositions appear to be p r o m i s i n g c a n d i d a t e materials for high dielectric constant fine-grained piezoelectric applications. lntroduct ion P e r o v s k i t e l e a d m a g n e s i u m n i o b a t e Pb(Mg~3Nby3)03, hereafter abbreviated PMN, belongs to a class of ferroelectric materials which exhibit a diffuse phase transition known as relaxor ferroelectricsl. The dielectric behavior of these materials have been widely investigated i n both single crystal and polycrystalline ceramic forms since first synthesized by Soviet workers in the late 1950s. PMN forms a solid solution with t h e normal ferroelectric PbTi03 (PT) (Curie temperature, T, -490 "C), allowing its transition to be raised to near room temperature with only small amounts of PT (< 10 mole a). Within the PMN-PT solid solution series, there exists a morphotropic phase boundary (MPB) near 33 mole % PT, separating rhombohedral and tetragonal phases2. In single crystals as well as the polycrystalline materials, compositions near the MPB exhibit unusually large dielectric and piezoelectric properties, similar to those observed in other lead based ferroelectrics such as Pb(ZrxTi1.,)O3 (PZT) and relaxor-PbTi03 systems, e.g., Pb(Ni ~3Nby3)03-PbTi03 (PNN-PT) and Pb(Znu3Nb&03-P b T i O 3 (PZN-PT). It is interesting to note that all relaxor-PT MPB compositions have Tmax'S in the range of 150 "C -180 "C, giving rise to a question of the underlying mechanism which is not fully understood a t this time.In recent years, device technology has being greatly developed for various applications and the scale of such devices including m u l t i l a y e r c a p a c i t o r s , electrostrictors, and piezoelectric transducers are getting smaller. Thus, fine grain size (c 1 l m ) materials with high dielectric constant and piezoelectric activity are desired.In conventional PZT piezo-materials, smaller grains tend to clamp out extrinsic contributions such as domain wall motion. Microstructural dependency on the properties is not expected in PMN-based ceramics since the underlying phenomena associated with relaxor ferroelectric behavior is on the order of -10 nm3.Observed grain size effects in relaxor materials have been attributed to a low dielectric constant grain...
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