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Detailed Program
Paper Number : LP-I08
Time Frame : 13:55~14:20
Presentation Date : Friday, 28, November
Session Name : Leadfree Piezoelectrics
Session Chair 1# : Soon-Jong Jeong
Session Chair 2# : Hiroyuki Shimizu
Enhanced Strain Properties of Relaxor Matrix Ferroelectric Composites in Bi-Based Lead-Free Piezoelectric Ceramics
Jae-Shin LEE
University of Ulsan
Keywords: Lead-free, Piezoelectric, Strain, Relaxor, Ferroelectric, Composites

Recently, Bi-perovskite ceramics have attracted much attention because of their large electric field-induced strains (EFIS) at ferroelectric (FE) – relaxor ferroelectric (RFE) phase boundaries. During the last decade, we found that many modified Bi1/2Na1/2TiO3 - Bi1/2K1/2TiO3 (BNT-BKT or BNKT) solid solutions exhibited abnormally large strain properties when there was a ferroelectric-relaxor (FE-R) crossover with increasing the modifier content [1]. In the case of A- or B-site impurities, the FE-R crossover was observed when the tolerance factor (t) of the perovskite structure was decreased by doping, whereas the FE state of unmodified BNKT remained stable when the dopant increased the t.
Despite the fact that BNKT-based ceramics have shown large normalized strains up to Smax/Emax = 876 pm/V at RT near the FE-R transition region [2], there still remain critical problems to be resolved for practical applications; large strain-field hysteresis and large electric-field to trigger large strain.
In order to overcome these issues, we attempted to prepare ceramic-ceramic composites by embedding FE particles in a relaxor matrix. The normalized strain Smax/Emax was remarkably enhanced by lowering the triggering field even though the maximum strain was almost unchanged. The ceramic-ceramic composite is believed to enlighten a new road to large strain lead-free alternatives of Pb-based actuator materials.


Figure 1. SEM and PFM images of a relaxor-ferroelectric BNKT composite.


References:

[1] H. B. Lee, D. J Heo, R. A. Malik, C. H. Yoon, H. S. Han, and J. S Lee, Ceram. Int. 39, Suppl. 1, s705 (2013).
[2] R. A. Malik, J. K. Kang, A. Hussain, C. W. Ahn, H. S. Han, and J. S. Lee, Appl. Phys. Express 7, 61502 (2014).
Acknowledgements :