Preparation And Poling Engineering Of High-Performance?K,Na?NbO₃-Based Piezoceramics

(K,Na)NbO3(KNN)-based piezoelectric ceramics have been used in various fields,due to the large piezoelectric response as well as high Curie temperature.In the present study,the effects of the addition of CaZrO3(CZ),various poling conditions and atmosphere sintering on KNN-based lead-free piezoceramics were investigated.First of all,the effect of the addition of CZ in(Na0.49K0.49Li0.02)(Nb0.8Ta0.2)O3(KNNLT)was studied.Optimum piezoelectric properties(d33 = 344 pC/N and kp = 47.3%)were obtained for the KNNLT-xCZ with x = 0.05 due to the polymorphism phase behavior(PPT)effect around room temperature.Then it was found that all of the samples doping around 5 mol%show high performance,which can ensure the stability and repeatability of the high performance for this lead-free piezoceramic system.Then,effect of various poling conditions on CaZrO3-modified KNN-based lead-free piezoceramics was investigated.It is found that the KNN ceramics can reach saturated polarization state under reduced poling field and time,compared with PZT due to its small c/a ratio.Including in the positive contribution of domain switching,the negative effect of domain pining which is caused by strong space charge accumulation is also verified.The poling behavior is the balance between positive and negative effects.In order to weaken the negative effects of poling process,atmosphere sintering was tried and the largest piezoelectric constantd33 was up to 390 pC/N.This would attribute to the decrease in the oxygen vacancies by sintered in the oxygen atmosphere.Moreover,good temperature stability for CZ5 sintered at oxygen atmosphere was found,and it is because a reduction in Pmax with temperature can be compensated by a stronger reduction in Pr with temperature.