Synergistic Electron Density and Oxygen Defect Regulation in Fluorite High‐Entropy Oxides for Superior Ionizing Radiation Shielding

Lightweight and lead‐free radiation shielding materials remain urgently needed. This work designed a fluorite high‐entropy oxide (FHEO) system through a combined computational–experimental route. Density functional theory based on special quasi‐random structures was used to identify thermodynamically stable fluorites from a wide compositional space. Their γ‐ray attenuation potential in polypropylene (PP) composites was then evaluated, and the best candidates were selected for ultrafast Joule‐heating synthesis. Guided by this workflow, LaSm‐1000/PP composite showed broad‐spectrum shielding performance and surpassed PbO/PP at identical loadings. Its linear attenuation coefficients were 5.67, 0.48, 0.38, and 0.34 cm −1 at 59.5, 662, 1173, and 1332 keV, respectively. X‐ray photoelectron spectroscopy and projected density of states revealed an electron density–oxygen defect synergy in optimized FHEO. Lattice distortion and uniform cation distribution suppressed oxygen defects, stabilized Bi 3+ and W 6+ , and broadened O 2p states. These electronic features enhanced photoelectric absorption at low energies and promoted Compton scattering at medium and high energies. The proposed design route provides an efficient and scalable strategy for next‐generation lead‐free radiation shielding materials.