La₂Hf₂O₇ Based TBC Materials with Near-Infrared Ultra-Low Transmittance for Thermal Radiation Shielding

As the thrust-weight ratios of aero-engines increase, the severe thermal radiation emitted by high-temperature gases (≥1800 K) poses a significant challenge for thermal barrier coating (TBC) materials. Traditional TBC materials, despite their reliable thermal insulation properties, are nearly transparent to infrared radiation, which leads to direct radiative heating of the metallic substrate, consequently reducing its service life. In response, a La₂Hf₂O₇-based ceramic doped with a NiFe₂O₄ second phase is developed to prevent the penetration of thermal radiation and achieve exceptional thermal radiation shielding properties. The experimental results exhibit that 85%La₂Hf₂O₇/15%NiFe₂O₄ possesses high absorptivity exceeding 0.85 across a broad wavelength range (0.2-14 µm), and ultra-low transmittance of 0.001 in the range of 0.4-2.5 µm. It attributes to the presence of multi-valent transition elements (Ni⁺/Ni²⁺ and Fe²⁺/Fe³⁺) in NiFe₂O₄, which significantly reduce the band gap width, enhancing photon absorption, scattering, and electron transition probability following infrared radiation absorption. These multifaceted contributions minimize radiative thermal conductivity to 1.55 W m⁻¹ K⁻¹, effectively shielding the radiative heat transfer. These advantages make this high-temperature thermal shielding strategy highly competitive for the next generation of TBC materials development and application.