Local Chemical Clustering Enabled Ultrahigh Capacitive Energy Storage in Pb-Free Relaxors

Designing Pb-free relaxors with both a high capacitiveenergy density(W (rec)) and high storage efficiency (& eta;)remains a remarkable challenge for cutting-edge pulsed power technologies.Local compositional heterogeneity is crucial for achieving complexpolar structure in solid solution relaxors, but its role in optimizingenergy storage properties is often overlooked. Here, we report thatan exceptionally high W (rec) of 15.2 J cm(-3) along with an ultrahigh & eta; of 91% can be achievedthrough designing local chemical clustering in Bi0.5Na0.5TiO3-BaTiO3-based relaxors.A three-dimensional atomistic model derived from neutron/X-ray totalscattering combined with reverse Monte Carlo method reveals the presenceof subnanometer scale clustering of Bi, Na, and Ba, which host differentiatedpolar displacements, and confirming the prediction by density functionaltheory calculations. This leads to a polar state with small polarclusters and strong length and direction fluctuations in unit-cellpolar vectors, thus manifesting improved high-field polarizability,steadily reduced hysteresis, and high breakdown strength macroscopically.The favorable polar structure features also result in a unique field-increased & eta;, excellent stability, and superior discharge capacity. Ourwork demonstrates that the hidden local chemical order exerts a significantimpact on the polarization characteristic of relaxors, and can beexploited for accessing superior energy storage performance.