Research On Preparation And Electric Properties Of Lead-free K_0.5Na_0.5NbO₃ Based Ceramics

Piezoelectric ceramics have been widely used in the fields such as transducer, sensors, nondestructive testing and communications technology etc. Pb(Zr,Ti)O3 solid solution (PZT) has been dominant in research and applications, but one of the major drawbacks of PZT materials is the lead content. Accordingly, these materials may be restricted in near future due to environment issues.In the field of lead-free piezoelectric ceramics, many researches focus on the alkali metal niobate-based materials.In this paper, sodium potassium niobate-based ceramics were selected as the experimental system.The preparation and poling process were researched. The crystal structures of KxNa1-xNbO3(KNN) ceramics showed orthogonal phase as x increased from 0.4 to 0.5.The highest piezoelectric properties were obtained in KNN50 .The optimal sintering temperature was between 1050℃and 1080℃.The better poling process was poled by applying dc field of 3kV/mm for 20 min in silicone oil bath at 120℃Lithium substitution on properties of KNN ceramics were investigated. K3LiNb6O17 phase which has a similar function as liquid phase was found in the specimens with x≥0.04.The piezoelectric properties of the specimens with x≥0.08 degraded due to the phase of LiNbO3.Furthermore,Lithium substitution lowed TO-T but increased Tc.The morphotropic phase boundary(MPB) was obtained in the specimens with x=0.06.MnO2 doped in KNLNST ceramics fined the size of grains, increased TO-T and TC and make ceramics"hard".The optimal piezoelectric properties were obtained from the specimens doped with 0.5mol% MnO2.The sintering temperature and loss tangent decreased but the mechanical quality factor(Qm) increased greatly in KNN-LS doped with CuO, which revealed the properties of KNN-LS ceramic"harder".KNLNST lead-free piezoelectric ceramics doped with 0.5mol% MnO2 were used for ultrasonic motors.The maximum output speed and power were 20mm/s and 0.5 Newton.