Hierarchical architectures in Cr³⁺-doped GdTaO₄ for boosted high-temperature thermal protection performance

The main purpose of thermal protection materials is to minimize heat conduction toward the substrate interior through low thermal conductivity, and to enhance heat radiation to the external environment via high emissivity. Herein, novel thermal barrier ceramic materials based on (Gd_1-xCr_x)TaO₄ with high emissivity and low thermal conductivity were synthesized via a solid-phase method. Among these samples, (Gd_0.95Cr_0.05)TaO₄ exhibited the lowest phonon thermal conductivity of 1.03 W·m^–1·K^–1 at 1600 °C and the highest emissivity of 0.80 across the 1–14 μm wavelength range at 800 °C, both of which enhanced its thermal insulation performance. The low phonon thermal conductivity of (Gd_0.95Cr0_.05)TaO₄ originated from the hierarchical architectures’ defect phonon scattering, including point defects, dislocations, domain boundaries and grain boundaries. The high emissivity of (Gd_0.95Cr_0.05)TaO₄ was dominated by high free-carrier absorption (band gap of 0.98 eV) and vibrational absorption (lattice distortion of 1.552%). Moreover, the introduction of Cr³⁺ induced d–d electron transitions and generated new absorption bands in the infrared region, thus enhancing thermal radiation. These results indicate that (Gd0.95Cr0.05)TaO4 is a promising candidate for use as an innovative thermal protection coating material at elevated temperatures.