Effects of Ge4+ acceptor dopant on sintering and electrical properties of (K0.5Na0.5)NbO3 lead-free piezoceramics
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Lead-free (K0.5Na0.5)(Nb1-xGe x )O3 (KNN-xGe, where x = 0-0.01) piezoelectric ceramics were prepared by conventional ceramic processing. The effects of Ge4+ cation doping on the phase compositions, microstructure and electrical properties of KNN ceramics were studied. SEM images show that Ge4+ cation doping improved the sintering and promoted the grain growth of the KNN ceramics. Dielectric and ferroelectric measurements proved that Ge4+ cations substituted Nb5+ ions as acceptors, and the Curie temperature (TC) shows an almost linear decrease with increasing the Ge4+ content. Combining this result with microstructure observations and electrical measurements, it is concluded that the optimal sintering temperature for KNN-xGe ceramics was 1020°C. Ge4+ doping less than 0.4 mol.%can improve the compositional homogeneity and piezoelectric properties of KNN ceramics. The KNN-xGe ceramics with x = 0.2% exhibited the best piezoelectric properties: piezoelectric constant d33 = 120 pC/N, planar electromechanical coupling coefficient kp = 34.7%, mechanical quality factor Qm = 130, and tanδ = 3.6%.
Keywordslead-free piezoelectric ceramics potassium sodium niobate doping sintering dielectric relaxation piezoelectric properties
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The authors thank Jianqiang Zhou for his technical help with SEM measurements. This work was supported by the National Natural Science Foundation of China (Grant No. 21371056) and the Fundamental Research Funds for the Central Universities (Grant No. 2015ZZD04).