Developing Excellent Thermo‐Optical Properties in Bi/Ta Doped AgNbO ₃ Ceramics for Adaptive Thermal Management

ABSTRACT Effective regulation of optical and thermal properties remains a crucial challenge for materials in variable temperature environments. Conventional thermal control materials, characterized by static thermo‐optical properties, often fail to meet the demands under dynamic thermal conditions. In this study, we achieve exceptional thermo‐optical properties in AgNbO ₃ ‐based ceramics (Ag _1‐x Bi _x/3 NbO ₃ with x = 0.20, ABN0.20), demonstrating a high emittance variation (Δε = 0.298) and temperature‐stable absorptance (Δα = 0.046) across a broad temperature range. Through integrated experimental analysis and DFT calculations, we investigate the effects of doping on lattice structure, phase transition temperature, and thermo‐optical properties. Key findings include: (i) The phase transition temperature decreases with decreasing ionic radius of the dopant, particularly that Bi ³⁺ and Ta ⁵⁺ ion doping significantly lowers the M ₁ –M ₂ phase transition temperature, stabilizing the antiferroelectric phase near room temperature. (ii) Dopants effectively narrow the bandgap of AgNbO ₃ , enhancing solar absorption. (iii) The d–p orbital hybridization between Ag(Nb)─O bonds governs emissivity through thermal disruption susceptibility. Strengthened hybridization expands the resonant area, thereby increasing infrared emission. These results demonstrate that orbital hybridization‐mediated tuning in doped AgNbO ₃ ceramics offers a promising pathway for developing adaptive thermal control systems, particularly for applications requiring real‐time emissivity modulation and solar‐thermal regulation.