Giant Strains in Non‐Textured (Bi_1/2Na_1/2)TiO₃‐Based Lead‐Free Ceramics

Abstract

Giant electric-field-induced strain of 0.70%, corresponding to a d33 * value of 1400 pm V(-1) , is observed in a lead-free (Bi1/2 Na1/2 )TiO3 -based polycrystalline ceramic. This is comparable to the properties of single crystals. An in situ transmission electron microscopy study indicates that the excellent performance originates from phase transitions under the applied electric fields.

Giant strain with low cycling degradation in Ta-doped [Bi1/2(Na0.8K0.2)1/2]TiO3 lead-free ceramics

“…24 Through finely tuning the composition and optimizing the thermal processing conditions on the same solid solution system, an extremely high strain of 0.70% at 50 kV/cm in {[Bi 1/2 (Na 0.84 K 0. 16 25 The electrostrain and d 33 * observed in this conventionally sintered, non-textured polycrystalline ceramic are comparable even with lead-free single crystals. 26,27 The Sr and Nb co-doped [Bi 1/2 (Na 1Àx K x ) 1/2 ]TiO 3 ceramics have complex compositions (containing six cations), which can lead to difficulties with reproducible properties in large-scale production.…”

“…25 Aliovalent doping and thermal vapor loss of volatile cations are the two apparent sources for these point defects. Specifically, the loss of Bi 3þ , Na þ , and K þ on the A-site of the ABO 3 perovskite structure at high temperature presumably generates A-site vacancies.…”

“…The strong frequency dispersion in e r at room temperature suggests a relaxor characteristic for all ceramics, which correlates well to the nanometer-sized domains revealed by TEM. Similar to Sr and Nb co-doped [Bi 1/2 (Na 1Àx K x ) 1/2 ]TiO 3 ceramics, 25 two anomalies appear on the dielectric constant curves, one at the thermal depolarization temperature, T d , and the other at the dielectric maximum temperature, T max . The incorporation of Ta shifts T d downwards to room temperature, but has a limited effect on T max .…”

“…26,27 The strain in the BNT-1.5Ta ceramic was also measured under unipolar electric fields and a slightly smaller d 33 * value of 1120 pm/V was observed at 50 kV/cm. Based on previous studies, 21,25 it can be suggested that the extremely large electrostrain in FIG. 4.…”

“…All grains examined are observed to be occupied by nanometer-sized domains, suggesting a macroscopic relaxor behavior, which is consistent with the previous work on Sr and Nb co-doped [Bi 1/2 (Na 1Àx K x ) 1/2 ]TiO 3 ceramics. 25 All the [112] diffraction patterns display two types of superlattice spots, the 1 = 2 {ooo}-type and the 1 = 2 {ooe}-type (o stands The selected area electron diffraction patterns are displayed as insets. Bright field TEM images of (h) BNT-1.0Ta and (i) BNT-1.5Ta with core-shell type microstructure along the [112] zone-axis.…”