High‐Strength Micron‐Thick Layered Ceramics with Ultralow Radiation Transmittance for Thermal Shielding Above 1273 K

Porous rare‐earth oxide films are promising for thermal insulation but suffer from high heat‐ray transparency and limited mechanical stability at extreme high‐temperatures. Here, an alternately stacked Y 3 NbO 7 /GdTaO 4 ceramic film is presented for thermal insulation above 1273 K by effectively scattering both phonons and photons. This layered ceramic film has a low thermal conductivity of 0.35 W m −1 K −1 and a minimized near‐infrared transmissivity of 0.5% at a thickness of 500 µm. Broadband photon backscattering (0.5–10 µm) is enabled by the hierarchical pores (1 and 5 µm), effectively suppressing radiative heat transfer while disrupting solid‐phase heat conduction. Heterogeneous interfaces further enhance phonon scattering due to mismatched local lattice vibrations. Additionally, atomic interdiffusion and ferroelastic domain alignment at pore‐free interfaces significantly improve bending strength tenfold to that of the state‐of‐the‐art fiber‐based aerogels with comparable thermal conductivity. These findings provide a design strategy for high‐temperature protection material with high phonon/photon shielding and mechanical robustness.