Local Atom Clusters Drive Supercritical Relaxor State in Lead‐Free Dielectrics for Giant Energy Storage

Perovskite relaxor ferroelectrics have emerged as the leading capacitive energy‐storage materials in pulsed‐power electronics and integrated energy systems. However, conventional relaxor design strategies encounter a fundamental trade‐off, wherein increasing compositional complexity to suppress hysteresis typically weakens local polar strength, thereby hindering the simultaneous realization of ultrahigh recoverable energy density ( W rec ) and efficiency ( η ). Herein, we demonstrate that sublattice‐hierarchical local atom clustering provides an effective approach to overcoming this limitation. By combining strong A ‐site disorder with Mg/Hf‐rich nanoregions on B ‐site sublattices, we embed atomic clusters within a relaxor ferroelectric matrix to stabilize a supercritical relaxor state. Through neutron total scattering techniques and atomic‐resolution electron microscopy, we reveal that local atom clusters not only enhance lattice distortion to form ultrafine polar nanodomains but, more importantly, strengthen the local random field to enable strong and highly reversible polarization. As a result, the designed lead‐free ceramic achieves an ultrahigh W rec of 17.03 J cm −3 and an excellent η of 93.5%, resulting in a superior figure of merit up to 262. The fast‐discharging capability and robust stability against temperature, frequency, and cycling further evidence its strong application potential. These findings identify local atom clustering as a general and powerful approach for designing high‐performance dielectric ceramic capacitors.