⟨ 001 ⟩ -oriented (K0.5Na0.5)(Nb0.97Sb0.03)O3 (KNNS) ceramics with a narrow orientation distribution (full width at half maximum=7.0°) were produced by templated grain growth using NaNbO3 templates. Excellent electromechanical properties were obtained from −70 °C to the polymorphic phase transition (PPT) at 160 °C. Textured KNNS ceramics show very high electromechanical coupling factors kp=0.64 and k31=0.37, high piezoelectric constants d33=208–218 pC/N and d31=−82 pC/N, and modest strain hysteresis (6.3%) at room temperature. These properties are superior to those of randomly oriented KNN-based ceramics with similar PPT temperatures.
phases to NaNbO 3 , PbTiO 3 , and BaTiO 3 perovskites were studied. Reaction of the AE001ae oriented Aurivillius phases with excess Na 2 CO 3 , Pb 3 (CO 3 ) 2 (OH) 2 , and BaCO 3 , respectively, yielded high-aspect-ratio perovskite microcrystals with AE001ae orientation. Only the Na 3.5 Bi 2.5 Nb 5 O 18 to NaNbO 3 conversion occurred directly, whereas TEM analysis of reacted BaBi 4 Ti 4 O 15 and PbBi 4 Ti 4 O 15 revealed previously unknown Aurivillius-type intermediate phases with Bi 2 O 2 2þ layers ∼86 and ∼78 A ˚apart, respectively. Observations from TEM and field emission SEM show that perovskite crystallites grow from multiple nucleation sites, but become slightly misaligned during growth. This misalignment is caused by a loss of epitaxy with the parent Aurivillius phase and subsequent exfoliation of the particles, likely caused by the expulsion of byproduct Bi 2 O 3 liquid on phase boundaries. This conversion process results in substantial microstructure damage, which is healed with an annealing step between 950 and 1050 °C. The pathway for formation of AE001ae oriented, polycrystalline or single-crystal perovskite platelets is illustrated in a general model for topochemical conversion of Aurivillius phases.
The figure-of-merits of ferroelectrics for transducer applications are their electromechanical coupling factor and the operable temperature range. Relaxor-PbTiO3 ferroelectric crystals show a much improved electromechanical coupling factor k33 (88~93%) compared to their ceramic counterparts (65~78%) by taking advantage of the strong anisotropy of crystals. However, only a few relaxor-PbTiO3 systems, for example Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3, can be grown into single crystals, whose operable temperature range is limited by their rhombohedral-tetragonal phase transition temperatures (Trt: 60~120 °C). Here, we develop a templated grain-growth approach to fabricate <001>-textured Pb(In1/2Nb1/2)O3-Pb(Sc1/2Nb1/2)O3-PbTiO3 (PIN-PSN-PT) ceramics that contain a large amount of the refractory component Sc2O3, which has the ability to increase the Trt of the system. The high k33 of 85~89% and the greatly increased Trt of 160~200 °C are simultaneously achieved in the textured PIN-PSN-PT ceramics. The above merits will make textured PIN-PSN-PT ceramics an alternative to single crystals, benefiting the development of numerous advanced piezoelectric devices.
Lead-free (K0.44Na0.52Li0.04)(Nb0.96−xTaxSb0.04)O3 piezoelectric ceramics have been synthesized by conventional solid state sintering process. Two morphotropic phase boundaries (MPBs) respectively corresponding to the orthorhombic to tetragonal and tetragonal to pseudocubic phases are observed with increasing x. The ceramics with x=0.20 between the two MPBs show significantly enhanced electrical properties, which are as follows: piezoelectric constant d33=252pC∕N, planar coupling coefficient kp=0.42, dielectric constant εr=1503, and dielectric loss tanδ=0.025, and they show good stability. Lead-free superthin buzzer disks have been prepared by using piezoceramic membrane with x=0.20. (K0.44Na0.52Li0.04)(Nb0.96−xTaxSb0.04)O3 ceramics are very promising as lead-free replacements for lead zirconate titanate.
Both low strain hysteresis and high piezoelectric performance are required for practical applications in precisely controlled piezoelectric devices and systems. Unfortunately, enhanced piezoelectric properties were usually obtained with the presence of a large strain hysteresis in BaTiO (BT)-based piezoceramics. In this work, we propose to integrate crystallographic texturing and domain engineering strategies into BT-based ceramics to resolve this challenge. [001] grain-oriented (BaCa)(TiZr)O (BCTZ) ceramics with a texture degree as high as 98.6% were synthesized by templated grain growth. A very high piezoelectric coefficient (d) of 755 pC/N, and an extremely large piezoelectric strain coefficient (d* = 2027 pm/V) along with an ultralow strain hysteresis (H) of 4.1% were simultaneously achieved in BT-based systems for the first time, which are among the best values ever reported on both lead-free and lead-based piezoceramics. The exceptionally high piezoelectric response is mainly from the reversible contribution, and can be ascribed to the piezoelectric anisotropy, the favorable domain configuration, and the formation of smaller sized domains in the BCTZ textured ceramics. This study paves a new pathway to develop lead-free piezoelectrics with both low strain hysteresis and high piezoelectric coefficient. More importantly, it represents a very exciting discovery with potential application of BT-based ceramics in high-precision piezoelectric actuators.
In this work, we report the electromechanical properties of /00lS C -textured (K 0.5 Na 0.5 ) 0.98 Li 0.02 NbO 3 (KNLN) and (K 0.5 Na 0.5 )(Nb 0.85 Ta 0.15 )O 3 (KNNT) ceramics produced by templated grain growth. Both materials show high texture quality (F 00l 5 98% and full-width at half-maximum [FWHM] 5 8.41 for KNLN, F 00l 5 99%, and FWHM 5 7.61 for KNNT) and enhanced piezoelectric response compared with randomly oriented ceramics. However, textured KNLN shows higher piezoelectric properties (d 33 5 192 pC/N, k p 5 0.63, k 31 5 0.39, d 31 5 À73 pC/N, d 33 Ã 5 208 pC/N) and higher phase transition temperatures (T oÀt 5 1551C, T c 5 4391C) than textured KNNT. The enhanced room-temperature piezoelectric properties are associated with low-strain hysteresis (4.0%), suggesting that /00lS C textured and poled orthorhombic KNLN may exhibit domain engineering character. The piezoelectric performance of textured KNLN with T oÀt 5 1551C is high and stable over a wide temperature range (À601-1001C), strongly favoring use of this material in device applications compared with the modified KNN-based materials with a T oÀt near room temperature.
D. Damjanovic-contributing editor
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