Structure, piezoelectric performance and liquid phase aid sintering of SiO_2 doped (K_(0.5)Na_(0.5)) NbO_3 lead-free ceramics

摘要

The structure, piezoelectric and sintering proprieties of Lead-free piezoelectric (K_(0.5)Na_(0.5)) NbO_3 (abbreviated as KNN) ceramic with additive SiO_2 (KNN-xSiO_2, 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 Si02 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 SiO_2 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%.