First-principles calculations of the electronic structure, chemical bonding, and thermodynamic properties of USiO4

Li Su,Bingyun Ao,Tao Gao,Lei Wan

doi:10.1063/5.0018203

Abstract

The density functional theory (DFT) + U method is adopted to study the electronic structure, magnetism, chemical bonding, and thermodynamic properties of USiO4. A bandgap of 3.1 eV is obtained by analyzing the band diagram of USiO4. The calculated structural parameters are consistent with the recent experimental results. The charge density and charge density differences are studied in order to analyze the chemical bonds in USiO4. The results indicate that interactions within USiO4 are mostly ionic and exhibit weak covalent character. In addition, phonon behavior is studied in detail. We predict phonon frequencies and assign and analyze the Raman-active and infrared-active modes at the Γ point. Furthermore, thermodynamic properties such as the internal energy ΔE, Helmholtz free energy ΔF, constant-volume specific heat CV, and entropy S are investigated in the region between 0 K and 1000 K. The results are expected to provide useful information for subsequent experiments on USiO4.

Highlights

With the increasing number of national nuclear energy research programs, the disposal of spent nuclear fuel (SNF) is one of the most vital issues associated with advanced nuclear fuel cycles.[1,2] SNF consists of 90% UO23 and is stored in deep geological repositories.[4]
It is obvious that the generalized gradient approximation (GGA) approach produces the lowest total energy for the FM phase
By comparing our results to the existing experimental values, we found that the parameter U is vitally important to the determination of electronic properties

Summary

Introduction

With the increasing number of national nuclear energy research programs, the disposal of spent nuclear fuel (SNF) is one of the most vital issues associated with advanced nuclear fuel cycles.[1,2] SNF consists of 90% UO23 and is stored in deep geological repositories.[4]. Over the past few years, coffinite (USiO4), a type of actinide-bearing mineral, has been the subject of extensive experimental investigation because of its utility in preventing spent nuclear fuel corrosion and its importance in geophysics. It is an important uraninite alteration mineral that is formed from UO2 in the presence of silica-enriched aqueous solutions and survives reducing conditions. The zircon-type USiO4 structure is an essential mineral phase that plays a vital role in determining the solubility of uranium from nuclear fuel that has been accidentally corroded by geological ground water.[8]. Accurate knowledge of the physical properties of coffinite provides a crucial reference for repository assessment

Methods

Results

Conclusion