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Title: Double hysteresis loop in Cu-doped K[sub 0.5]Na[sub 0.5]NbO₃ lead-free piezoelectric ceramics
Authors: Lin, D
Kwok, KW 
Chan, HLW 
Keywords: Potassium compounds
Sodium compounds
Copper compounds
Dielectric hys
Vacancies (crystal)
Dielectric polarisation
Solid-state phase transformations
Issue Date: 4-Jun-2007
Publisher: American Institute of Physics
Source: Applied physics letters, 4 June 2007, v. 90, 232903, p. 1-3 How to cite?
Journal: Applied physics letters 
Abstract: In this letter the authors report the observation of double hysteresis loops in Cu-doped K[sub 0.5]Na[sub 0.5]NbO₃(KNN) ceramics. Unlike other ferroelectric titanates (e.g., BaTiO₃), aging is not required for the ceramic to exhibit the double-loop-like characteristics. Based on the symmetry-conforming principle of point defects, it is suggested that defect dipoles are formed by the acceptor dopant ions-Cu[sup 2+] and O²ˉ vacancies along the polarization direction after the diffuse tetragonal-orthorhombic phase transition of the ceramic. Because of the low migration rates of defects, the defect dipoles remain in the original orientation during the P-E loop measurement, providing a restoring force to reverse the switched polarization. The defect dipoles also provide “pinning” effects in the normal piezoelectric activities. As a result, the ceramic becomes “hardened,” exhibiting an extraordinarily high mechanical quality factor (2500), while the other piezoelectric properties remain reasonably good: electromechanical coupling coefficients k[sub p]=39%, k[sub t]=47%, and piezoelectric coefficient d[sub 33]=82 pC/N.
ISSN: 0003-6951
DOI: 10.1063/1.2746087
Rights: © 2007 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in D. Lin & H.L.W. Chan, Appl. Phys. Lett. 90, 232903 (2007) and may be found at
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