Hydrothermal synthesis and characterization of (1-x)K0.5Na0.5NbO3-xBi0.5Na0.5TiO3 lead-free ceramics

Lead-free piezoelectric powders (1 - x)(K0.5Na0.5) NbO3-x(Bi0.5Na0.5)TiO3 ((1 - x)KNN-xBNT, x = 0.01 - 0.08) were firstly synthesized by hydrothermal method and their ceramics were subsequently prepared after sintering and polarizing treatment. The phase structure and the micro-morphology of as-prepared powders and ceramics were characterized by X-ray diffraction and field emission scanning electron microscopy. The effects of preparing conditions such as titanium source, hydrothermal temperature and BNT doping amount (x, mol%) on phase formation and micro-morphology of (1 - x)KNN-xBNT powders were investigated in detail. It is showed that (1 - x)KNN-xBNT (x = 0.05) powders were successfully prepared by using TiO2 as titanium source when the temperatures were controlled from 210 degrees C to 230 degrees C. Two phases of K-rich (K, Na)NbO3 and Na-rich (K, Na) NbO3 coexisted, and they gradually transformed into only K-rich (K, Na) NbO3 with the increase of BNT content. After sintering, the (1 - x)KNN-xBNT ceramics exhibited single (1 - x) KNN-xBNT phase, and a morphotropic phase boundary (MPB) between the orthorhombic and tetragonal phases was identified in the composition range of 0.02 <= x <= 0.05 where optimal piezoelectric constant d(33) was obtained. (C) 2013 Elsevier B.V. All rights reserved.