In Situ Measurement of Full‐Spectrum Emissivity for Thermoelectric Materials below Room Temperature

Abstract Accurate determination of emissivity is essential for reliable thermal conductivity measurements in thermoelectric materials. Current spectroscopic techniques are restricted by limited wavelength ranges and cannot provide comprehensive characterization. This study develops a robust in situ method to measure full‐spectrum emissivity of solid‐state materials between 160 and 300 K. For Bi 2 Te 3 ‐based thermoelectric materials, emissivity values of 0.62–0.65 (N‐type) and 0.46–0.66 (P‐type) are obtained, with precision of 4%. Validation experiments using standard quartz samples with and without gold coating, and P‐type (Bi,Sb) 2 Te 3 samples with different roughness demonstrate critical influence of surface conditions on emissivity. Importantly, measurements of thermal conductivity and emissivity of the same Bi 2 Te 3 sample under identical condition show that ignoring radiative correction leads to a dramatic 40% overestimation of thermal conductivity at 300 K. This work provides a practical method for precise emissivity characterization that enables more accurate thermoelectric material evaluation.