Study On Preparation And Performance Of KNN-LS Lead-free Piezoelectric Ceramics

This essay elaborated the exploration and preparation of high-performance lead-freepotassium sodium niobate piezoelectric ceramics,(Na0.474K0.474Li0.052)Nb0.948Sb0.052O3(shortfor0.948KNN-0.052LS或KNN-LS), which were synthesized in sol-gel method then sinteredto ceramics. Effect of stuctural properties of KNN-LS lead-free piezoelecrtic ceramicsadjusted by adding excess K and Na and compoud admixture of Cu and Zn were alsoinvestigated.Oxalic acid was investigated as a more excellent complexing agent than citric acid in Sbcomplexing. The optimal value of PH, complexing agent, including optimal volume ratio ofoxalic acid, ethylene glycol and polyethylene glycol were studied at the same time. In case ofPH value maintaining2.5-3.0, polyethylene glycol adding1wt%, oxalic acid/Nb molar ratioachieving3:1and oxalic acid/ethylene glycol molar ratio achieving1:2, all the perfomance ofKNNLS gel solution got best results.The KNN-LS piezoelectric ceramics were synthesized in the optimal experimentalcondition above by sol-gel method in order to studied the optimal sintering temperature, andthis temperature was considered as1030℃. Effect of piezoelectric and dielectric properties of(Na0.474K0.474Li0.052)Nb0.948Sb0.052O3-xNa2CO3,(Na0.474K0.474Li0.052)Nb0.948Sb0.052O3-yK2CO3（short for KNNLS-xNa2CO3、KNNLS-yK2CO3）,which were synthesized in sol-gel methodby adding exess K, Na in the optimal experimental condition above were investigated.As increase of exess Na content, the XRD peak intensity of KNNLS piezoelectricceramics first increased then decreased, with a transformation phase structure from tetragonalphase to orthorhombic phase. The piezoelectric coefficient d33, dielectric constant εralsohad a first increased then decreased tendency and dielectric losses tanδ first decreased thenincreased with increasing of exess Na. When exess Na achieved2mol%, the XRD peakintensity became sharpest and the piezoelectric coefficient d33, dielectric constant εr,dielectric losses tanδ achieved98.1pC/N,609(f=1KHz),0.0715(f=1KHz) respectivelyAs increase of exess K content, the XRD peak intensity of KNNLS piezoelectricceramics didn’t exhibit an obvious phase transformation. The piezoelectric coefficient d33,dielectric constant εralso had a first increased then decreased tendency and dielectric losses tanδ first decreased then increased with increasing of exess K. When exess K achieved1mol%, the XRD peak intensity became sharpest and the piezoelectric coefficient d33,dielectric constant εr, dielectric losses tanδ achieved95.5pC/N,613(f=1KHz),0.1193(f=1KHz) respectively. It’s illustrated that adding fine exess K, Na served as a compensatingrole for sintering vaporizing of KNNLS piezoelectric ceramics.With small amount of compoud admixture of Cu and Zn, the phase structure of somesample of KNNLS-0.02Na2CO3had a second phase K4CuNb8O22from simple perovskitephase before. With increasing of amount of Cu and Zn incorporated, the peak position ofXRD pattern had a little shift to small degree, and it suggested the increase of interplanarspacing. Meanwhile in SEM photoes it’s showed that grain size tend to be well-distributedand enlarged as the increasing of Cu, Zn. When the amout of Cu, Zn achieved0.6mol%,0.5mol%and sintering temperature was850℃, the d33of KNNLS-0.02Na2CO3with Cu andZn incorporated achieved the best140pC/N，and the desity reached the highest as well.The d33, εr,tanδ, Kp, Qmof KNNLS-0.02Na2CO3with Cu and Zn incorporated wasinvestigated by using orthogonal experimental method. The analysis shows that optimal resultof d33、εr、tanδ was the D9sample,A3B3C2, according to amout of Cu, Zn achieved0.6mol%,0.5mol%and sintering temperature was850℃. Through vertification experiment andanalyzied from piezoelectric and dielectric properties, it’s the balance chioce to consider D9sample as the best experimental result.