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

doi:10.1007/s11706-017-0371-2

Front. Mater. Sci.

2017, Vol. 11

Issue (1) : 59-65 https://doi.org/10.1007/s11706-017-0371-2

RESEARCH ARTICLE

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

Kepi CHEN(

),Yanlin JIAO

School of Energy, Power and Mechanical Engineering, North China Electric Power University, Beijing 102206, China

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Abstract

Lead-free (K_0.5Na_0.5)(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 (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

Corresponding Author(s): Kepi CHEN

Online First Date: 12 January 2017 Issue Date: 22 January 2017

Cite this article:

Kepi CHEN,Yanlin JIAO. Effects of Ge⁴⁺ acceptor dopant on sintering and electrical properties of (K_0.5Na_0.5)NbO₃ lead-free piezoceramics[J]. Front. Mater. Sci., 2017, 11(1): 59-65.

URL:

https://academic.hep.com.cn/foms/EN/10.1007/s11706-017-0371-2
https://academic.hep.com.cn/foms/EN/Y2017/V11/I1/59

Fig.1 SEM images of KNN-xGe ceramics sintered at different temperatures.

Fig.2 XRD patterns of KNN-xGe ceramics sintered at 1020°C.

Fig.3 Variation of the dielectric constant as a function of temperature for KNN-xGe ceramics sintered at 1020°C.

Fig.4 Variation of the Curie temperature T_C for KNN-xGe ceramics sintered at 1020°C.

Fig.5 Plots of ln(1/ϵ−1/ϵ_m) vs. ln(T−T_m) for KNN-xGe ceramics.

Fig.6 Variation of the degree of diffuseness γ for the KNN-xGe ceramics at 1020°C.

Fig.7 P?E hysteresis loops of KNN-xGe ceramics sintered at 1020°C (data were measured at 1 Hz and room temperature): (a)x = 0, 0.8%, 1.0%; (b)x = 0.2%, 0.4%, 0.6%.

Fig.8 Electrical properties of KNN-xGe ceramics sintered at 1020°C: (a)d₃₃; (b)k_p; (c)Q_m; (d) tanδ.

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