Negative temperature dependence of ultra-low near-infrared emissivity induced by oxygen ion migration

Achieving stable low infrared emissivity at high temperatures remains a challenge, because thermally activated electronic and lattice excitations generally lead to increased infrared emission. Here, we report a class of defective fluorite ceramics, Ln₃NbO₇ (Ln = Y, Yb, Ho, Er), that exhibit an anomalous negative temperature dependence of infrared emissivity, characterized by a decrease in emissivity with increasing temperature. Notably, these ceramics maintain an ultra-low near-infrared emissivity (1–6 μm) of approximately 0.1 across a broad temperature range from 298 K to 1275 K, significantly outperforming existing advanced ceramics such as ZrB₂. This unique behavior is attributed to the thermal activation of long range oxygen ion migration, which disrupts phonon transport and suppresses radiative heat dissipation. Confirmed by temperature resolved spectroscopy and simulations demonstrate that enhanced ionic mobility at elevated temperatures induces strong phonon scattering, thereby minimizing radiative losses. These findings offer a new design pathway for advanced thermal protection ceramics.