Study On Sintering Properties And Sm Doping Modification Of KNN-Based Lead-Free Piezoelectric Ceramics

Traditional piezoelectric ceramic zirconium lead titanate（PZT）has been widely used in transducers,filters,and sensors fields,but due to the toxicity of lead,the latest environmental standards put forward the need for lead-free piezoelectric ceramics.This research is based on potassium niobate sodium（KNN）lead-free piezoelectric ceramics,in view of the problems of difficult sintering and poor electrical performance of KNN ceramics,the effects of Li⁺,Ta⁵⁺co-doping of KNN ceramics on the microscopic morphology,dielectric and piezoelectric properties of 0.95(K_0.55,Na_0.45)Nb O₃-0.05Li Ta O₃（abbreviate to KNN-LT）ceramics were studied.At the same time,in order to further enhance the temperature stability performance of ceramics,the rare earth element Sm is introduced in the A-site of KNN-LT ceramics to obtained piezoelectric ceramic materials with good sintering performance,excellent piezoelectric activity and low temperature dependence.The mechanism of Sm doped modified KNN-LT ceramics is analyzed in detail from the perspectives of lattice distortion and ferroelectric phase transformation.The main works of this article are as follows:（1）KNN-LT ceramics were prepared by sintering at different temperatures such as 1050,1075,1100,1125,1150°C.The ceramic structure is orthorhombic-tetragonal phase coexistence after 1100°C sintered,and as the sintering temperature increases,the ceramic structure changes to a single tetragonal phase.Meanwhile,the sintering temperature has an obvious influence on the grain size of the ceramic.When the sintering temperature is low,the growth energy of the grains is insufficient,and the grains are finely dispersed.When the sintering temperature is high,the elements in the ceramic volatilize violently,resulting in the generation of internal porosity.The microstructure of the ceramic after sintering at 1100°C is that the small grains are sandwiched between the large grains,with the highest density is 4.28 g/cm³.The KNN-LT ceramic obtained the best electrical properties after sintering at 1100°C,d₃₃=171p C/N,K_p=33.23,tanδ=0.08,P_r=18.91μC/cm²,E_c=6.25 k V/cm,therefore,it can be considered that 1100°C is the optimal sintering temperature for KNN-LT ceramics.（2）A-site Sm³⁺ions doping is introduced into KNN-LT ceramics.It was found that Sm can significantly reduce the grain size in the ceramic and increase the optimal sintering temperature of the ceramic after analyzing the doped KNN-LT ceramic.As the doping content of Sm increases from 0 mol.%to 1 mol.%,the optimal sintering temperature for ceramics increases from 1100°C to 1150°C.When the doping amount of Sm is 0.4 mol.%,a fine grain and uniformly arranged microstructure can be obtained,and the ceramic density is the highest,about 4.35 g/cm³.At the same time,the Sm³⁺ions can increase the tetragonality of the KNN-LT ceramic lattice.When the amount of Sm doping is 0～0.4 mol.%,the ceramic phase structure is orthogonal-tetragonal phase coexistence.As the doping amount exceeds 0.4 mol.%,the ceramic structure is transformed into a single tetragonal phase.In addition,when the doping amount of Sm is 0.4 mol.%,the phase change temperature region of KNN-LT ceramics can be widened.At this time,the ceramic is still near the PPT region,and its internal phase structure is two phases coexisting,but the phase change temperature zone is raised to20°C to near 125°C,so the KNNLT-Sm0.4 ceramic improves temperature stability while obtaining the best piezoelectric performance.d₃₃=197 p C/N,K_p=43.72%,Q_m=106.54,tanδ=0.078.In addition,the incorporation of Sm³⁺ions can weaken the ferroelectric properties of KNN-LT ceramics and strengthen the relaxation properties of ceramics.