Significantly enhanced recoverable energy storage density in potassium-sodium niobate-based lead free ceramics

Ceramic-based dielectric materials are regarded as the best candidates for advanced pulsed power capacitors because of their excellent mechanical and thermal properties. Nevertheless, lead-free bulk ceramics show relatively low recoverable energy storage density (W-rec < 2 J cm(-3)) owing to their low dielectric breakdown strength (DBS < 200 kV cm(-1)). In order to significantly increase W-rec, we proposed a strategy (compositions drive the grain size to submicrometer) to improve the DBS of lead-free ceramics. In this work, (1-x)(K0.5Na0.5) NbO3-xSrTiO(3) (KNN-ST) ceramics were chosen as a representative to verify the validity of this strategy. The (1-x) KNN-xST ceramics (x-0.15 and 0.20) with submicrometer grains (about 0.3 mu m) were prepared using pressureless solid state sintering. A large W-rec (4.03 J cm(-3)) and DBS (400 kV cm(-1) with a thickness of 0.2 mm) were achieved for 0.85KNN-0.15ST ceramics. The value of 4.03 J cm(-3) is superior to all other W-rec in lead-free bulk ceramics and 2-3 times larger than that of other lead-free bulk ceramics. A large W-rec (3.67 J cm(-3)) and energy storage efficiency (72.1%) were simultaneously achieved for 0.80KNN-0.20ST ceramics. The results confirm that the (1-x) KNN-xST ceramics (x-0.15 and 0.20) are desirable materials for advanced pulsed power capacitors. The findings in this study could push the development of a series of KNN-based ceramics with enhanced DBS and W-rec in the future. On the other hand, this work could broaden the applications of KNN materials in a new field.