⟨ 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.

Abstract

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