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arXiv · 2603.02441

The contribution of nitrogen Frenkel-pair formation to the high-temperature heat capacity of uranium mononitride

Mohamed AbdulHameed·Benjamin Beeler
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Abstract

The high-temperature heat capacity of uranium mononitride (UN) remains uncertain due to conflicting measurements and models above ~1700 K. To assess whether intrinsic defect formation contributes to the observed superlinear behavior of $C_P(T)$, we perform large-scale molecular dynamics simulations using two interatomic potentials to quantify nitrogen diffusion and Frenkel-pair populations from 1800--2600 K. Both models show increasing anion mobility, but the Tseplyaev potential yields substantially larger Frenkel concentrations, producing a defect heat-capacity contribution of up to ~10 J/(mol-K). This defect-driven term is consistent with the curvature seen in historical correlations and recent ab initio results, suggesting that nitrogen sublattice disorder provides a plausible intrinsic mechanism for the high-temperature heat capacity of UN.

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Mohamed AbdulHameed, Benjamin Beeler. 2026-03-02. The contribution of nitrogen Frenkel-pair formation to the high-temperature heat capacity of uranium mononitride. https://arxiv.org/abs/2603.02441

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