Structural Evolution and Thermo‐Optical Dynamics in Bi 3+ /Ta 5+ Co‐Doped AgNbO 3 for Intelligent Thermal Management

ABSTRACT Intelligent thermal control materials with adaptable thermo‐optical properties are critical for variable‐temperature thermal management. Silver niobate (AgNbO 3 ) is a promising candidate due to its phase‐transition‐linked thermo‐optical behavior. Herein, Bi 3+ and Ta 5+ co‐doped (Ag 1‐ x Bi x /3 )(Nb 1‐ y Ta y )O 3 ceramics were investigated using a combined experimental and DFT calculation approach. From this, a high‐performance ANBi20Ta15 smart thermal control material was successfully synthesized, which achieved an emittance variation as high as Δ ε = 0.304 while maintaining good thermal cycling stability. Structural characterizations confirmed a pure orthorhombic perovskite phase and successful dopant incorporation, with lattice distortion and increased oxygen vacancies. The co‐doping strategy has tuned phase transition temperatures and stabilized the antiferroelectric M 2 phase to room temperature. The bandgap was reduced to 2.47 eV, enhancing solar absorptivity, while total hemispherical emittance exhibited strong temperature dependence. The magnitude of emittance variation is strongly correlated with the evolution of the Ag–O and Nb–O bonds, with a large variation resulting from extensive bond evolution. Concurrently, temperature‐induced bandgap narrowing and enhanced O–Ag/O–Nb orbital resonance promote infrared‐active phonon vibrations, which govern the thermo‐optical response. This work provides an effective co‐doping strategy for optimizing AgNbO 3 ‐based ceramics, offering a feasible route for high‐performance intelligent thermal control materials.