Effect of high energy milling process on microstructure and piezoelectric/dielectric properties of K0.475Na0.475Li0.05NbO3 solid solution

K0.475Na0.475Li0.05NbO3 (abbreviated as NKLN) ceramic of near the morphotropic phase boundary (MPB) composition was synthesized by two different processes. The first one is the high energy milling [sometimes abbreviated as HEM hereafter] process, which involves mixing the starting materials and milling the calcined powder using a high energy nano-mill, in order to obtain nano-sized particles. The second one is a conventional mixed oxide method. The HEM process of the starting materials lowered the calcination temperature to the extent of 200 °C as compared with conventionally fabricated NKLN. The particle size of the powder, exposed to the HEM process, reduced to 40 nm, whereas the conventionally ball-milled powder had a larger size of 420 nm after the mixing process. Furthermore, the HEM process improved the reaction activity and homogeneity of the materials used throughout the process, accompanying the enhancement of the sintering density, grain uniformity, and the decrease of grain size. In order to investigate the effects of the HEM process on the electric properties of NKLN ceramics, the dielectric and piezoelectric properties of sintered specimens fabricated by two different processes were evaluated. It was found that the properties of the nano-sized NKLN ceramic near the MPB composition were increased by the modified method, showing the maximum values of d33=179 pC/N, kp=34% and K33T=440 compared with 132 pC/N, 29%, and 400, respectively in the conventional process. Further evidence for the grain size effect was investigated by the polarization–electric field curve at room temperature. The remnant polarization for the nano-sized NKLN specimen had a higher value of 24.3 μC/cm2 compared with that of 13.7 μC/cm2 for conventional NKLN, whereas the coercive field had a similar value. The modified mixing and milling method was considered to be a new and promising process for lead-free piezoelectric ceramics owing to their excellent piezoelectric/dielectric properties.