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

Lead-free piezoelectric Bi-0.5(Na0.78K0.22)(0.5)(Ti1-xHfx)O-3 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-max/E-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. (C) 2010 The Japan Society of Applied Physics