ABSTRACT Zirconium diboride (ZrB 2 ) is a promising material for extreme‐environment applications, yet its intrinsic high‐temperature thermophysical behavior remains uncertain: Experiments are highly sensitive to processing conditions, simulations omit key mechanisms, and both rarely reach ultrahigh temperatures. Here, we predict the thermal conductivity ( κ ), heat capacity, and thermal expansion of ZrB 2 from 300 to 3500 K using first principles, explicitly incorporating phonon and electron transport, high‐order phonon scattering, and temperature‐dependent force constants. We estimate that the intrinsic room‐temperature polycrystalline κ is ∼169 W m −1 K −1 , exceeding the highest experimental value (∼141 W m −1 K −1 ) limited by microstructural defects, and decreases monotonically to 64.5 W m −1 K −1 at 3500 K. Remarkably, this magnitude rivals that of the most refractory metal, tungsten, whereas ZrB 2 's density is three times lower, underscoring its potential for lightweight thermal management. Importantly, electrons dominate heat transport across the entire temperature range, carrying ∼61% of κ at 300 K and ∼91% at 3500 K, indicating that previous research focused solely on phonon engineering may have overlooked the governing role of electronic conduction. The Lorenz number varies non‐monotonically with temperature, deviating significantly from the Sommerfeld value L 0 , indicating that the common assumption of constant L 0 may lead to inaccurate thermal–electrical correlations. Phonons dominate heat capacity, though electronic contributions become notable above 1300 K (≈6% at 3500 K). For phonon transport, heat is primarily carried by acoustic modes (≈89% at 300 K) and limited by three‐phonon and electron‐phonon scattering. Counter‐intuitively, four‐phonon scattering is negligible at room temperature, despite the large acoustic–optical gap, because broad optical bands preserve key three‐phonon channels, though the four‐phonon scattering becomes significant at high T . Interestingly, isotopic purification would raise phonon thermal conductivity by ∼23%, whereas temperature‐dependent force constants increase it by 28% at room temperature. Finally, compared with related systems, ZrB 2 exhibits nearly twice the thermal conductivity of ZrC at room temperature, mainly because of its significantly higher electronic contribution while maintaining a higher phonon component despite its more complex structure. Although κ for ZrB 2 decreases with temperature, whereas that of ZrC rises, ZrB 2 remains superior across the entire temperature range. This work clarifies the intrinsic thermal transport physics of ZrB 2 and highlights its exceptional potential for high‐temperature thermal‐management and aerospace applications.
Lee et al. (Fri,) studied this question.