Compositionally engineered core@shell Ba(Zr, Ti)O3 for concurrent giant electrocaloric effect and ultra-wide operational window

Simultaneously achieving large adiabatic temperature change (ΔT) and broad temperature span (T_span) remains a key challenge in eco-friendly electrocaloric ceramics. This work demonstrates a compositionally ordered core-shell design in Zr-doped BaTiO₃ (BaZr_xTi_1-xO₃, 0.10 ≤ x ≤ 0.25) that synergistically enhances both parameters. Precise Zr gradient engineering induces phase transition overlap and strengthens relaxor behavior through controlled diffusion. The compositionally sandwiched core@double-shell architecture achieves a record ΔT of 6.6 K maintained over an ultra-wide T_span > 70 °C (ΔT ≥ 90 % ΔT_max), representing a ∼ 2-fold T_span extension compared to conventional homogeneous counterparts. Remarkably, the system exhibits the highest EC efficiency (η, 19.81) and refrigerant capacity (RC, 603.1 J kg⁻¹) among lead-free electrocaloric ceramics. These breakthroughs originate from the coupled effects of Zr-modulated phase transition characteristics and interfacial polarization enhancement in the hierarchical structure. Our findings provide a generalizable microstructural design strategy for high-performance solid-state cooling materials.