Valence‐State Engineering in Praseodymium‐Yttria‐Zirconia for Radiative Heat Suppression

Above 1000 °C, radiative heat transfer can dominate in semi‐transparent thermal protection ceramics such as yttria‐stabilized zirconia (YSZ). Here, we demonstrate a Pr valence engineering strategy in the Pr 0.2 Y x Zr 0.8‐x O 2‐δ (x = 0, 0.2, 0.4, 0.6) system that reduces the transmittance of the semitransparent ceramic in 0.4–2.5 µm, making it nearly radiation‐opaque. By tuning x to increase the Pr 4+ fraction, unoccupied Pr 4f states shift into the bandgap, yielding a maximum broadband absorptance exceeding 90% (0.4–2.5 µm), an optical gap as low as 0.62 eV, and an extinction coefficient > 10 5 m −1 . At 1573 K, the photon thermal conductivity of the highly absorbing composition reaches only < 5% of that of 8YSZ, while its phonon thermal conductivity is even lower. This work establishes a design strategy for suppressing radiative heat transfer in high‐temperature thermal protection materials.