Thermophysical–Infrared Emission Synergistic Optimization Mechanism of Sc2O3–CeO2 Co-Doped YSZ Ceramics

Conventional 8YSZ thermal barrier ceramics suffer from limited phase stability and insufficient infrared radiation regulation at high temperatures. Sc2O3 doping can reduce thermal conductivity and improve phase stability, but the improvement remains limited because the fixed-valence substitution of Sc3+ cannot effectively increase defect concentration or regulate carrier behavior. In this work, CeO2 with tunable valence states was incorporated into the Sc-stabilized YSZ system to realize the synergistic modulation of lattice thermal conductivity and photon thermal conductivity. A series of Sc2O3–CeO2 co-doped YSZ ceramics were fabricated via solid-state sintering, and the effects of co-doping on phase structure, defect evolution, thermal conductivity, infrared emissivity, and bandgap characteristics were systematically investigated. The results show that all co-doped samples maintained a stable tetragonal fluorite structure with relative densities higher than 96%. Among them, Sc0.08Ce0.005Y0.005Zr0.91O2 exhibited the best comprehensive performance. Its thermal conductivity at 1000 °C reached 2.073 W·m−1·K−1, which was 11.9% lower than that of conventional 8YSZ. Meanwhile, the average infrared emissivity in the 3–5 μm band increased to 0.779. XPS analysis indicated that Ce incorporation promoted oxygen-vacancy formation, which enhanced phonon scattering and reduced lattice thermal conductivity. In addition, co-doping narrowed the band gap and facilitated carrier excitation, thereby strengthening infrared absorption and emission behavior. The enhanced infrared emissivity further contributed to the suppression of radiative thermal transport at elevated temperatures. This work demonstrates that Sc2O3–CeO2 co-doping provides an effective strategy for simultaneously regulating phonon transport and photon transport in YSZ-based ceramics. The results provide new insight into the design of advanced thermal barrier materials with low thermal conductivity and enhanced high-temperature infrared radiation performance.