Structural dynamics of Schottky and Frenkel defects in ThO2: a density-functional theory study

Samuel Moxon, Jonathan Skelton, Joshua S. Tse, Joseph Flitcroft, A. Togo, David J. Cooke, E. Lora Da Silva, Robert M. Harker, Mark T. Storr, Stephen C. Parker, Marco Molinari

Research output: Contribution to journalArticlepeer-review

Abstract

Thorium dioxide (ThO²) is a promising alternative to mixed-oxide nuclear fuels due to its longer fuel cycle and resistance to proliferation. Understanding the thermal properties, in particular the thermal conductivity, under reactor conditions is critical to the success of any candidate fuel material. ThO2 has a higher thermal conductivity and thus a lower operating temperature than other fuel systems. However, the presence of defects in real materials directly influencesthe structural dynamics and physical properties, and the impact of defects on the properties of ThO2 are largely unexplored. We have employed densityfunctional theory calculations to study the structure and energetics of the intrinsic Schottky and Frenkel defects in ThO2 and their impact on the thermophysical properties. We identify the anion Frenkel defect to be the most stable, and we identify characteristic spectral signatures of the defects in the phonon dispersions and infrared spectra. We further employ two approximate models developed in previous work to assess the impact of the defects on the thermal transport and find that both types of defect are predicted significantly to reduce the thermal conductivity. The methodology we present facilitates prediction of thethermophysical and transport properties of defective materials at an atomistic level, and should be readily transferrable to other
existing and in-development nuclear fuel systems.

Keywords: nuclear fuels, thorium dioxide, defect chemistry, defect energetics, structural dynamics, phonon spectra, thermal
transport
Original languageEnglish
JournalJournal of Materials Chemistry A
Early online date7 Jan 2022
DOIs
Publication statusPublished - 7 Jan 2022

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