Relaxor based fine grain piezoelectric materials

Abstract

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...

Phase formation and microstructure of Nd+3 doped Pb(Mg1/3Nb2/3)O3 prepared by sol–gel method

“…Similarly, Kim et al [17] reported that La-doping at\1 mol% resulted in the decrease in the grain size of PMN and PMN-PT ceramics. The behavior was explained by solid-solution impurity drag mechanism [17].…”

“…They interpreted their observations such that using La +3 based admixture determines the incorporation of the La +3 on the Pb +2 site acting as the donor dopant [2]. Similarly, Kim et al [17] reported that La-doping at\1 mol% resulted in the decrease in the grain size of PMN and PMN-PT ceramics. The behavior was explained by solid-solution impurity drag mechanism [17].…”

“…Their results showed that doping of neodymium (Nd +3 ) resulted in a slight decrease in the grain size and a lowering of the dielectric constant [16]. Kim et al [17] and Branileau et al [2] studied effect of lanthanum (La +3 ) additions on the phase formation of PMN ceramics. The former study indicated that the presence of La +3 cations implied an increase in the short range ordering, resulting negative space-charge balance into the ordered domains in PMN [3].…”

SPICE Model Identification Technique of a Cheap Thermoelectric Cell Applied to DC/DC Design with MPPT Algorithm for Low-Cost, Low-Power Energy Harvesting

“…This last effect was the first to be exploited, in the realization of actuators as speakers, but recently is being studied for the possibility of applying piezoelectric materials in contact with vibration sources to recover energy from them. For this purpose, more efficient piezoelectric materials, such as lead zirconate titanate (PZT) [26,27] or relaxor-based ferroelectric single crystals, have been studied [28].…”