Composition-driven electronic-state engineering of refractory Zr1-xHfxN for broadband space thermal control

Refractory broadband reflectors are desirable for reducing radiative heat loads in long-duration space cryogenic systems. Here, composition-dependent radiative regulation in rocksalt Zr 1-x Hf x N is investigated using first-principles calculations combined with an experimentally calibrated intraband Drude correction. Hf substitution continuously transfers near-Fermi metal-d orbital weight from Zr-4d to Hf-5d states while producing non-monotonic changes in the electronic and dielectric responses. These effects generate a broadband optical optimum at Zr 0.25 Hf 0.75 N, which exhibits an AM0-weighted solar reflectance of 85.80%, a solar absorptance of 0.1420, and a Planck-weighted infrared emittance of 0.0448 at 300 K that remains nearly unchanged from 300 to 400 K. The coincident solar and infrared optima demonstrate that composition engineering can simultaneously suppress solar absorption and thermal-infrared emission, providing a design route for refractory reflective surfaces for space cryogenic thermal management.