# The First Principal Calculation of the Temperature-Dependent Crystalline Defect Evolution in UN

## TL;DR

This study uses first-principles calculations to explore how temperature affects defect formation in uranium nitride crystals, revealing that high temperatures promote spontaneous defect formation.

## Contribution

The paper presents the first principal calculation of temperature-dependent crystalline defect evolution in UN.

## Key findings

- Elevated temperatures significantly reduce defect formation energies in UN crystals.
- Interstitial and divacancy defects show negative formation energies at 1780 K, suggesting spontaneous formation.
- U interstitial defects cause a 5.1% lattice expansion at 0 K and significant lattice distortions.

## Abstract

This study systematically investigates the influence of temperature on the defect formation mechanisms in uranium nitride (UN) crystals using first-principles calculations. The formation energies and lattice distortion characteristics of various defects at 0 K and 1780 K were calculated by constructing models of perfect crystals as well as vacancy, interstitial, antisite, and divacancy defects. The results demonstrate that elevated temperatures significantly reduce defect formation energies, with interstitial and divacancy defects exhibiting negative formation energies at 1780 K, indicating a tendency for spontaneous formation. The U interstitial defect induces the most pronounced lattice expansion of 5.1% at 0 K. Furthermore, interstitial defects cause the most significant lattice distortions, while Schottky defects exhibit the lowest formation energy. The current study provides theoretical insights into the defect behavior of UN fuel under high-temperature service conditions and offers valuable guidance for optimizing sintering process parameters.