Ultrahigh energy storage in high-entropy ceramic capacitors with polymorphic relaxor phase Ultrahigh–power-density multilayer ceramic capacitors (MLCCs) are critical components in electrical and electronic systems. However, the realization of a high energy density combined with a high efficiency is a major challenge for practical applications. We propose a high-entropy design in barium titanate (BaTiO 3 )–based lead-free MLCCs with polymorphic relaxor phase. This strategy effectively minimizes ...