Double hysteresis loop in Cu-doped K0.5Na0.5NbO3 lead-free piezoelectric ceramics

Abstract

In this letter the authors report the observation of double hysteresis loops in Cu-doped K 0.5 Na 0.5 NbO 3 ͑KNN͒ ceramics. Unlike other ferroelectric titanates ͑e.g., BaTiO 3 ͒, 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 2+ and O 2− 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 ͑2500͒, while the other piezoelectric properties remain reasonably good: electromechanical coupling coefficients k p = 39%, k t = 47%, and piezoelectric coefficient d 33 =82 pC/N.

Antiferroelectric-like properties and enhanced polarization of Cu-doped K0.5Na0.5NbO3 piezoelectric ceramics

“…13) and is subsequently confirmed by the EPR spectrum. 14,15 Non-switchable DCs that are aligned opposite to the spontaneous polarization (P s ) direction provide the driving force for domain backswitching after the removal of the external electric field, similar to the antiferroelectric behavior.…”

“…Moreover, double P-E loops have also been reported in some acceptor-doped ferroelectrics without aging, such as in K þ -doped PbZr x Ti 1Àx O 3 (PZT) 11,12 and Cu 2þ -doped K 0.5 Na 0.5 NbO 3 (KNN) ceramics. 13 This phenomenon has been explained on the basis of the high mobility of defect dipoles, which could reorient easily after the formation of domain patterns. [11][12][13] Accordingly, aging is not required for the ceramics to exhibit double P-E loops.…”

“…13 This phenomenon has been explained on the basis of the high mobility of defect dipoles, which could reorient easily after the formation of domain patterns. [11][12][13] Accordingly, aging is not required for the ceramics to exhibit double P-E loops. In the present work, we studied the P-E loops and dielectric aging behaviors of KNN ceramics with Cu doping.…”

Aging effect evolution during ferroelectric-ferroelectric phase transition: A mechanism study

“…Information on the nature of the aging process can be obtained by studying the changes in the polarization -electric field (P-E) hysteresis loops which occur with aging. It is well known that after aging, a number of ferroelectric materials, such as Pb-based, 1-3 BaTiO 3 /(Ba, Sr)TiO 3, 4, 5 KNbO 3 -based, 6,7 and Bi-based 8,9 ferroelectrics, exhibit similar constricted P-E loops, regardless of their crystal structure and of their ionic species. The striking similarity of the aging effect in different ferroelectric perovskites was believed to originate from a general symmetry-conforming tendency of point defects, as stipulated by the symmetryconforming short-range ordering (SC-SRO) principle.…”

External field effects on aging phenomenon of acceptor-doped BaTiO3 ceramics

“…The prominent studies of Ren group further show that the microscopic origin of the volume effect arises from a symmetry conforming short-range ordering (SC-SRO) principle, which provides the driving force for the migration of OVs. [8][9][10]16,17 As we all know, the relaxation of OVs is a thermally and electrically activated process, which is an important factor affecting the aging behavior. Many studies have reported the variations of P-E loops and electrostrain with temperature and frequency.…”