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Detailed Program
Paper Number : LP-O06
Time Frame : 17:20~17:32
Presentation Date : Friday, 28, November
Session Name : Leadfree Piezoelectrics
Session Chair 1# : Chang Won Ahn
Session Chair 2# : Tonshaku Tou
Enhanced Low-Field Strain in Lead-Free Ferroelectric-Relaxor Composite Ceramics
Thi Hinh DINH
University of Ulsan
Keywords: Piezoelectric, Composite, Relaxor, Strain, Ceramics

Recently, BNKT ceramics have attracted much attention because of their large electric field-induced strains (EFIS) at ferroelectric (FE) – relaxor ferroelectric (RFE) phase boundaries. However, a critical problem that hinders their practical application to actuators is the fact that large strain in Bi-based lead-free ceramics is obtained only at high electric fields sufficient to induce a FE-RFE phase transition. To lower the critical field (Ecrit) that can cause the FE-RFE phase transition, FE-RFE composite ceramics were studied in this work. The effects of 0.82(Bi1/2Na1/2)TiO3-0.18(Bi1/2K1/2)TiO3 (BNKT) modification on the dielectric and piezoelectric properties of lead-free Bi0.5(Na0.385K0.09Li0.025)(Ti0.975Ta0.025)O3 (BNKLTT) ceramics were investigated as a function of BNKT content x in a range of 0, 0.1,0.2, 0.3, and 1. BNKT-modified BNKLTT powders were synthesized using a conventional solid-state reaction method. Ceramic disks were sintered at 1175 oC for 2 h in air. As the BNKT content x increased from 0 to 0.3, the relative density of a fired specimen was decreased from 99 % to 95 %. X-ray diffraction analysis revealed that undoped BNKT ceramics correspond to a mixture of tetragonal and rhombohedral symmetry because of reflection at about 40o and 46o show the feather of peak splitting, which could be pertained to the (111)/(-111) reflection of the rhombohedral phase and (002)/(200) reflection of tetragonal phase peaks. Interestingly, bipolar strain versus electric field (S-E) measurement showed that the normalized electric field-induced strain (Smax/Emax) was increased from 274 pm/V of pure BNKLTT to 756 pm/V for x=0.2 and then decreased with further BNKT modification. More interestingly, unipolar S-E loop showed a maximum Smax/Emax of 761 pm/V for x=0.3 at 4 kV/mm (Fig.1) and 833 pm/V for x=2 at 5 kV/mm. BNKLTT-BNKT composite ceramics show large strain under low electric field, which is comparable to that of soft lead zirconate titanate (PZT) ceramics, promising for lead-free actuator applications.
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