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The polarization switching characteristics of lead-free a(Bi1/2Na1/2)TiO3−bBaTiO3−c(Bi1/2K1/2)TiO3 (abbreviated as
BNBK 100a/100b/100c) ferroelectric ceramics are investigated. This is achieved through examining their polarization
and strain hystereses inside and outside the morphotropic phase boundary (MPB). The total induced electrostrain (&egr;33,total)
and apparent piezoelectric charge coefficient (d33) first increase dramatically and then decrease gradually as the BNBK
composition moves from the tetragonal phase to the MPB and then to the rhombohedral phase. The measured
polarization hystereses indicate that the BNBK compositions situated near the rhombohedral side of the MPB typically
possess higher coercive field (Ec) and remanent polarization (Pr), while the compositions situated near the tetragonal side
of the MPB possess higher apparent permittivity. Adverse effects on the ferroelectric properties are observed when
BNBK is doped with donor dopants such as La and Nb. On the contrary, intricate hysteresis behaviors are observed when
acceptor dopant Mn is introduced into BNBK. Under an alternating electric field of ±5.0 MVm-1, BNBK 85.4/2.6/12, a
composition well within the MPB, exhibits an &egr;33,total of ~0.14%, an apparent d33 of 295 pCN-1, an Ec of 2.5 MVm-1 and a
Pr of 22.5 &mgr;Ccm-2. These notable ferroelectric property values suggest a candidate material for lead-free actuator
applications. The present study provides a systematic set of hysteresis measurements which can be used to characterize
the switching behaviors of BNBK-based lead-free ferroelectrics.
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