Effects of Hafnium Substitution on Dielectric and Electromechanical Properties of Lead-free Bi0.5(Na0.78K0.22)0.5(Ti1-xHfx)O3 Ceramics

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Lead-free piezoelectric Bi0.5(Na0.78K0.22)0.5(Ti1-xHfx)O3 ceramics (abbreviated as BNKTH-$100x$, $x=0--0.05$) were prepared by the conventional solid-state reaction method. The effects of Hf substitution on the crystal structure and electromechanical properties were investigated. The X-ray diffraction patterns of the BNKTH-$100x$ ceramics revealed a single-phase perovskite structure with no evidence of secondary phases. The temperature-dependent dielectric curves of the BNKTH-$100x$ ceramics were found to broaden with increasing Hf concentration. The electric-field-induced strain of the BNKTH-$100x$ ceramics increased up to $x=0.03$ and then decreased. An enhanced electric-field-induced strain of 0.38% is observed for the BNKTH-3 ceramic. The corresponding normalized strain ($S_{\text{max}}/E_{\text{max}}=d_{33}^{*}$) for this composition was 475 pm/V at an applied electric field of 80 kV/cm. The BNKTH-3 ceramic can be considered as a promising candidate material for lead-free electromechanical applications.
2010-04-25