Study of phonons in irradiated epitaxial thin films of UO2

Abstract

We report experiments to determine the effect of radiation damage on the phonon spectra of the most common nuclear fuel, UO2. We have irradiated thin (∼ 300 nm) epitaxial films of UO2 with 2.1 MeV He 2+ ions to 0.15 dpa and a lattice swelling of ∆a/a ∼ 0.6 %, and then used grazingincidence inelastic X-ray scattering to measure the phonon spectrum. We succeeded to observe the acoustic modes, both transverse and longitudinal, across the Brillouin zone. The phonon energies, in both the pristine and irradiated samples, are unchanged from those observed in bulk material. On the other hand, the phonon linewidths (inversely proportional to the phonon lifetimes), show a significant broadening when comparing the pristine and irradiated samples. This effect is shown to increase with phonon energy across the Brillouin zone. The decreases in the phonon lifetimes of the acoustic modes are roughly consistent with a 50% reduction in the thermal conductivity.

Tuneable correlated disorder in alloys

“…% Mo) to investigate the effect of correlated static distortions on the dynamic properties. The data were collected in grazing-incidence inelastic x-ray scattering studies [34,44]. Representative constant Q scans along q = [001] p are shown in Fig.…”

“…The GI-IXS technique is one we have used previously with epitaxial films of UO 2 [34]. The data were collected over two experiments using Si(999) and Si(888) monochromator reflections, respectively.…”

X-ray synchrotron radiation studies of actinide materials

“…16 and Wong et al (2003)] was a major achievement, especially since the theoretical work was actually published in advance (Dai et al, 2003), and gave the first major 'credibility test' to the DMFT theory at that time (2003). More recently, the development of grazing-incidence IXS has led to important new information on the radiation damage in UO 2 (Rennie et al, 2018a) and on the complexity of the U-Mo alloy system . The sensitivity of these experiments is outstanding; especially considering the sample mass is less than 100 mg.…”

“…High-resolution inelastic X-ray scattering (IXS) at thirdgeneration synchrotron radiation sources is a well established technique for mapping phonon branches with meV energy resolution. High-performance spectrometers using crystals in near-backscattering geometry and efficient focusing optics (Burkel, 2000) allow one to measure phonon dispersion curves in crystals with volumes as small as 10 À4 mm 3 and in epitaxial thin films less than 500 nm thick (d 'Astuto et al, 2002;Rennie et al, 2018a). Compared with neutrons, this is a crucial advantage for studying radioactive materials or, in general, systems for which large single crystals are not available, or high pressure limits the crystal size.…”

Phonon Lifetimes throughout the Brillouin Zone at Elevated Temperatures from Experiment andAb Initio

“…Experimental determinations of phonon linewidths Γ (which are inversely related to phonon lifetimes as τ ¼ 1=πΓ) employ for instance Raman and infrared spectroscopy, which are highly accurate but restricted to the Γ point [13]. Probing the linewidth over the full Brillouin zone requires to use neutrons or x rays (specifically for small sample volumes [14]) as probes, where the focus lies often on electron-phonon scattering [12,15] or defect scattering [16]. In contrast, investigations of anharmonic phonon-phonon scattering over large regions of reciprocal space for unary elements at high temperatures have been reported up to now only for K [17], Li [18], and Cu [19].…”