Sandwich‐Like CNTs/Carbon@Si₃N₄ Porous Foam for Temperature‐Insensitive Electromagnetic Wave Absorption

Abstract Despite considerable efforts to tune the morphology and composition from the macroscopic level to the nanoscale level of electromagnetic wave‐absorbing materials (EWMs), achieving strong and wide‐bandwidth absorption under a temperature‐variant environment remains extremely difficult due to the temperature‐sensitive electromagnetic‐absorbing mechanisms that involve dipole polarization and conductive loss. Here, by integrating the highly conductive carbon nanotubes (CNTs) networks and the temperature‐stable silicon nitride (Si₃N₄) protective layer, a CNTs/amorphous carbon@Si₃N₄ (C‐CNT‐Si₃N₄) porous foam composed of sandwich‐like Si₃N₄/C‐CNT/Si₃N₄ strut, which exhibits excellent temperature‐insensitive electromagnetic‐absorbing properties from room temperature to 600 °C, is demonstrated. To be specific, the value of the minimum reflection loss is always lower than −50 dB, and a temperature‐insensitive effective absorbing bandwidth covering the whole X band throughout a thickness range of 4.8–6.1 mm is achieved. The superior temperature‐insensitive electromagnetic‐absorbing property is due to the synergistic effects of irregular polarization loss derived from lattice vacancies and heterogeneous interface, slightly increased conductive loss derived from decreasing carrier mobility, and increasing carrier concentration under a rising temperature environment.