Structure, piezoelectric performance and liquid phase aid sintering of SiO 2 doped (K 0.5 Na 0.5 ) NbO 3 lead-free ceramics

The structure, piezoelectric and sintering proprieties of Lead-free piezoelectric (K0.5Na0.5) NbO3 (abbreviated as KNN) ceramic with additive SiO2 (KNN–xSiO2, x = 0, 0.25, 0.50, 0. 75, 1.00, 1.50, 2.00 and 3.00 mol%) were investigated. Though it has a high melting point, the SiO2 was found to be effective on the sintering and piezoelectric performance of KNN lead-free ceramics. The structure characterization indicating that low concentration doping (<2.00 mol%) may not change KNN perovskite structure and liquid phase have appeared between crystalline grains. Furthermore, the sizes of crystalline grains gradually increased and reached to maximum when x = 0.75 mol% with indistinct grain boundaries on account of liquid phase. And the density properties of KNN ceramic were dramatically enhanced because of occurrence of liquid phase. The dielectric properties have achieved improvement obviously due to large resistivity and decreased structure loss results from the appearance of liquid phase as well. And ferroelectric properties have still achieved to enhancement including increased remnant polarization P r and decreased coercive field E c when appropriate SiO2 was added into KNLTN ceramic. We obtained the maximum value of piezoelectric coefficient d 33 (115 pC/N) and converse piezoelectric coefficient d * 33 when doping concentration approached to 0.75 mol%.