Effects of Ge4+ acceptor dopant on sintering and electrical properties of (K0.5Na0.5)NbO3 lead-free piezoceramics

摘要

Lead-free (K0.5Na0.5)(Nb1-x Ge-x)O-3 (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 (T-C) 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 degrees 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 d(33) = 120 pC/N, planar electromechanical coupling coefficient k(p) = 34.7%, mechanical quality factor Q(m) = 130, and tan delta = 3.6%.