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Detailed Program
Paper Number : LP-P10
Time Frame : 12:00~13:30
Presentation Date : Friday, 28, November
Session Name : Leadfree Piezoelectrics
Session Chair 1# : -
Session Chair 2# : -
Hardening Effects and Associated Lattice Defects in Lead-free (Na0.53K0.47)NbO3 Piezoelectric Ceramics
Mr. Gyung Hyun Ryu
Changwon National University
(Na,K)NbO3 (NKN)-based ceramics are considered a most promising candidate for lead-free piezoceramics due to their high Curie temperature (TC), low coercive electric field (EC), and large piezoelectric coefficient (d33). Recently, many studies for enhancing piezoelectric properties of NKN-based ceramics have been made progress by controlling polymorphic phase transition (PPT), and morphotropic phase boundary (MPB). In spite of these efforts, NKN-based materials still have a potential problem, high leakage current. Reason for the high conductivity is highly related with the formation of lattice defects during sintering process at high temperature. It is well accepted that oxygen vacancies are main defects as charge carriers which make the ceramic leaky. In addition, oxygen vacancies cause the ferroelectricity degradations, such as fatigue, imprint, and retention loss. In this study, we studied influences of lattice defects on ferroelectric and piezoelectric properties of undoped (Na0.53K0.47)NbO3 (NKN) ceramic. Change of polarization and bipolar strain values as a function of bipolar cycling suggests interesting phenomena, charge migration and hardening effects with internal bias field. Possible defects in NKN ceramic were investigated using electrical conductivity versus oxygen partial pressure at various temperatures. Room temperature current density and its hysteresis showed bipolar cycling dependence.
Acknowledgements : This work was supported by a National Research Foundation of Korea Grant funded by the Korea Government (2011-0030058).