Piezoelectric characterization of lead-free ferroelectric ceramics

Abstract

The challenge to develop high piezoelectric sensitivity and lead-free composition ferro-piezoelectric ceramics has recently dragged new attention to some classic ferroelectrics. Here, Ba(CexTi1-x)O3 (Ce-BT) and 0.94(Bi1/2Na1/2)TiO3-0.06BaTiO3 (BNBT6) ceramics were piezoelectrically characterized from measurements of complex impedance at electromechanical resonances and their analysis by Alemany et al. software. The reconstruction of the spectra for each resonance is used as an accuracy test of the set of calculated coefficients, quantitatively characterized by the regression factor (R2) of such reconstruction to the experimental spectrum. Piezoelectric activity at room temperature (RT) was observed for Ce-BT with x=0.06 and 0.1, ferroelectrics with T(ε´max)>RT, but also for x=0.2 with T(ε´max)<RT, which confirms its relaxor character (Ps¹0 for T³T(ε´max)). BNBT6 fine grained ceramics (~1 μm) were prepared from nanopowder obtained by sol-gel autocombustion. Results obtained for the fine grained ceramic hot-pressed at 800ºC for 2 h and recrystallized at 1050°C for 1 h are d33=148 pCN-1 and kp=26.8%. Despite of its lower grain size, the properties of this material are comparable with those reported for coarse grained ceramics obtained by sintering at T>1100°C. Some measurement issues, as the role of the mode coupling on the characterization results, illustrated for the shear mode of a thickness poled plate, are discussed