Thi Hinh Dinh

Comparison of Ferroelectric and Strain Properties between BaTiO3- and BaZrO3-Modified Bi1=2(Na0:82K0:18)1=2TiO3 Ceramics

Effects of BaTiO3 (BT) and BaZrO3 (BZ) modification on the crystal structure and electromechanical properties of lead-free Bi1/2(Na0.82K0.18)1/2TiO3 (BNKT) ceramics were compared within a doping range of 0–5 mol %. The differences between BT- and BZ-modification effects were clearly observed in polarization and electric field-induced strain hysteresis loops. BZ-modification induced a gradual transition from a ferroelectric to a nonpolar phase, resulting in an abnormal enhancement in the electric field-induced strain (EFIS) just after the transition. However, all BT-modified specimens showed strong ferroelectricity without abnormal enhancement in EFIS. The results suggest that Zr doping-induced B-site strains play a significant role in the ferroelectric-to-nonpolar phase transition in the Bi-perovskite.

Enhanced Low-Field Strain in Bi-Based Lead-Free Ferroelectric-Relaxor Composites

To improve the strain properties of Bi-based lead-free ceramics at lower electric fields, ferroelectric 0.82(Bi1/2Na1/2)TiO3-0.18(Bi1/2K1/2)TiO3 (BNKT) seed particles were embedded in Bi0.5(Na0.385K0.09Li0.025)(Ti0.975Ta0.025)O3 (BNKLTT) ceramics exhibiting relaxor behaviour using a conventional solid-state reaction. The unipolar strain versus electric field hysteresis loops of the BNKT-BNKLTT composites resulted in a maximum Smax/Emax of 761 pm/V at 4 kV/mm when 30 wt.% BNKT particles were added, which was higher than that of the single ferroelectric or relaxor phase.

Composition dependence of electric-field-induced structure of Bi1/2(Na1−xKx)1/2TiO3 lead-free piezoelectric ceramics

Microscopic origins of the electric-field-induced strain for three compositions of Bi1/2(Na1−xKx)1/2TiO3 (x = 0.14, 0.18, and 0.22) (BNKT100x) ceramics have been compared using in situ high-energy (87.12 keV) X-ray diffraction. In the as-processed state, average crystallographic structure of BNKT14 and BNKT18 were found to be of rhombohedral symmetry, while BNKT22 was tetragonal. Diffraction data collected under electric field showed that both the BNKT14 and BNKT18 exhibit induced lattice strain and non-180° ferroelectric domain switching without any apparent phase transformation. The BNKT22 composition, in addition to the lattice strain and domain switching, showed an electric-field-induced transformation from a tetragonal to mixed tetragonal-rhombohedral state. Despite the difference in the origin of microscopic strain responses in these compositions, the measured macroscopic poling strains of 0.46% (BNKT14), 0.43% (BNKT18), and 0.44% (BNKT22) are similar. In addition, the application of a second poling...

Effect of Ta Doping on Piezoelectric Properties of Lead-Free (K 0.5 Na 0.5 )NbO 3 Ceramics

We investigated the effect of Ta doping on the dielectric and piezoelectric properties of lead-free (K0.5Na0.5)NbO3 ceramics prepared using a conventional ceramic processing. X-ray diffraction analysis revealed that Ta was perfectly substituted into Nb-sites in the range of 0 to 20 at%. As Ta content in the KNN increased, the sinterability of KNN ceramics was significantly degraded while the Ta doping enhanced the piezoelectric constant d33, planar mode piezoelectric coupling coefficient (kp), and electromechanical quality factor (Qm). The highest values for d33, kp, and Qm was found to be 156 pC/N, 0.37, and 155, respectively.