Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/418
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 
Issue Date: 4-Jun-2007
Source: Applied physics letters, 4 June 2007, v. 90, 232903, p. 1-3
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.
Keywords: Potassium compounds
Sodium compounds
Copper compounds
Dielectric hys
Piezoceramics
Vacancies (crystal)
Dielectric polarisation
Solid-state phase transformations
Piezoelectricity
Publisher: American Institute of Physics
Journal: Applied physics letters 
ISSN: 0003-6951
EISSN: 1077-3118
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 http://link.aip.org/link/?apl/90/232903
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