Effects of Ge⁴⁺ acceptor dopant on sintering and electrical properties of (K_0.5Na_0.5)NbO₃ lead-free piezoceramics

Abstract

Lead-free (K_0.5Na_0.5)(Nb_1−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 (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°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 k_p = 34.7%, mechanical quality factor Q_m = 130, and tanδ = 3.6%.

Keywords

lead-free piezoelectric ceramics / potassium sodium niobate / doping / sintering / dielectric relaxation / piezoelectric properties

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Higher Education Press and Springer-Verlag Berlin Heidelberg