The influence of lattice defects, recombination, and clustering on thermal transport in single crystal thorium dioxide

Abstract

Thermal transport is a key performance metric for thorium dioxide in many applications where defect-generating radiation fields are present. An understanding of the effect of nanoscale lattice defects on thermal transport in this material is currently unavailable due to the lack of a single crystal material from which unit processes may be investigated. In this work, a series of high-quality thorium dioxide single crystals are exposed to 2 MeV proton irradiation at room temperature and 600 °C to create microscale regions with varying densities and types of point and extended defects. Defected regions are investigated using spatial domain thermoreflectance to quantify the change in thermal conductivity as a function of ion fluence as well as transmission electron microscopy and Raman spectroscopy to interrogate the structure of the generated defects. Together, this combination of methods provides important initial insight into defect formation, recombination, and clustering in thorium dioxide and the effect of those defects on thermal transport. These methods also provide a promising pathway for the quantification of the smallest-scale defects that cannot be captured using traditional microscopy techniques and play an outsized role in degrading thermal performance.

Phase and defect evolution in uranium-nitrogen-oxygen system under irradiation

“…However, other loop nucleation and destruction mechanisms could be at play. One of them includes in-cascade formation of loops that results in continued increase of loop density, which has been reported in proton irradiated ThO2 [88].…”

Thermal conductivity reduction in (Zr$_{0.25}$Ta$_{0.25}$Nb$_{0.25}$Ti$_{0.25}$)C high entropy carbide from extrinsic lattice defects

“…Fig. 2 is calculated for a baseline set of parameters D = 3.70 mm 2 /s and κ = 9.14 W/m•K for the pristine materials, with a 10% reduction in D and κ in the defect-bearing layer, and assuming a 14 nm thick deposited gold film (with corresponding thermal conductivity [28,29]). An ∼10 nm gold film was chosen as the set point as the sensitivity to a "sandwiched" thermal layer is higher when the transducer layer is thin; 14 nm was eventually deposited on these irradiated samples.…”

“…The general trend of a larger decrease in thermal conductivity at lower irradiation temperatures is consistent with expectations from most material systems where extrinsic structural defect production is driven by radiation bombardment. Namely, higher irradiation temperatures increase the mobility and therefore the recombination of any Frenkel defects or small clusters generated due to displacement damage, leaving fewer thermal scattering sites [28,35,36]. Using the simplified assumption that κ e is unaffected by structural defects and the entire reduction is due to phonon scattering, the fractional reduction in lattice thermal conductivity is plotted in Fig.…”

The In Situ Ion Irradiation Toolbox: Time-Resolved Structure and Property Measurements

“…Of possible methods to record thermophysical material properties, laser-based photothermal or photoacoustic methods have been identified as some of the most promising to deploy as in situ ion irradiation tools. A variety of these methods have been used to study ion irradiation effects ex situ including time domain thermoreflectance (TDTR), 117 spatial domain thermal reflectance (SDTR), 118 and laser-based resonant ultrasound spectroscopy. 119 Each of these methods share characteristics of being all-optical, non-destructive measurements conducted without contact with the specimen of interest.…”