A Highly Deficient Medium‐Entropy Perovskite Ceramic for Electromagnetic Interference Shielding under Harsh Environment

Abstract Materials that can provide reliable electromagnetic interference (EMI) shielding in highly oxidative atmosphere at elevated temperature are indispensable in the fast‐developing aerospace field. However, most of conductor‐type EMI shielding materials such as metals can hardly withstand the high‐temperature oxidation, while the conventional dielectric‐type materials cannot offer sufficient shielding efficiency in gigahertz (GHz) frequencies. Here, a highly deficient medium‐entropy (ME) perovskite ceramic as an efficient EMI shielding material in harsh environment, is demonstrated. The synergistic effect of entropy stabilization and aliovalent substitution on A‐site generate abnormally high concentration of Ti and O vacancies that are stable under high‐temperature oxidation. Due to the clustering of vacancies, the highly deficient perovskite ceramic exhibits giant complex permittivity and polarization loss in GHz, leading to the specific EMI shielding effectiveness above 30 dB/mm in X‐band even after 100 h of annealing at 1000 °C in air. Along with the low thermal conductivity, the aliovalent ME perovskite can serve as a bifunctional shielding material for applications in aircraft engines and reusable rockets.