Improving high-field strain and temperature stability on KNN-based ceramics sintered in reducing atmosphere via defect engineering

High-field strain and its temperature stability of (1–x) K0.48Na0.52Nb0.96Ta0.04O3-xBaZrO3+8%MnO+3%ZrO2 (in mole, KNNT-xBZ+8Mn) ceramics sintered in reducing atmosphere are improved simultaneously via defect design in A and B site. There is a conducting type transition from n-type to p-type at x = 0.07. The BaZrO3 dopant not only induces the increase of defects (ZrNb′, BaNa·, BaK·) concentration, but also results in the increase of defect (MnNb‴) concentration, because more Mn ions as +2 oxidation state in ceramics is triggered by BaZrO3 doping modification. Defect dipoles (MnNb′′′−Vo··, ZrNb′-Vo··, BaNa·-VNa′, BaK·-VK′) in poled and aged ceramics enhance the reversibility of the non–180° domains switching, which increases the high-field strain of KNNT-xBZ+8Mn ceramics. The reversibility of non–180° domain switching can be preserved to high temperature due to stable defect dipoles (BaNa·-VNa′, BaK·-VK′) in A-site. The KNNT-xBZ+8Mn ceramics at x = 0.07 show the largest high-field strain coefficient (543 pm/V@20 kV/cm) and the highest temperature stability (125 °C). The KNNT-xBZ+8Mn ceramic is a lead-free material with great potential to be applied in the fabrication of multilayer ceramic actuators with Ni inner electrodes in the future.