Supercritical Relaxor Nanograined Ferroelectrics for Ultrahigh‐Energy‐Storage Capacitors

Supercritical relaxor nanograined ferroelectrics are demonstrated for high-performance dielectric capacitors, showing record-high overall properties of energy density ≈13.1 J cm-3 and field-insensitive efficiency ≈90% at ≈74 kV mm-1 and superior charge-discharge performances of high power density ≈700 MW cm-3 , high discharge energy density ≈6.67 J cm-3 , and ultrashort discharge time <40 ns at 55 kV mm-1 . Ex/in situ transmission electron microscopy, Raman spectroscopy, and synchrotron X-ray diffraction provide clear evidence of the supercritical behavior in (Na,K)(Sb,Nb)O3 -SrZrO3 -(Bi0.5 Na0.5 )ZrO3 ceramics, being achieved by engineering the coexistence of multiple local symmetries within the ergodic relaxor zone. The vanished difference between the ground relaxor state and the high-field supercritical state eliminates polarization hysteresis. The supercritical evolution with electric field enables a highly delayed polarization saturation with continuously increased polarization magnitudes. The results demonstrate that such a design strategy of compositionally induced and field-manipulated supercritical behavior can be generalizable for developing desirable energy-storage dielectrics for applications in ceramic/film capacitors.