Alpha-recoil damage in zirconolite (CaZrTi<sub>2</sub>O<sub>7</sub>)

Lumpkin, G. R.; Ewing, Rodney C.; Chakoumakos, Bryan C.; Greegor, R.B.; Lytle, F. W.; Foltyn, E.M.; Clinard, F.W.; Boatner, L. A.; Abraham, M. M.

doi:10.1557/jmr.1986.0564

Cited by 89 publications

(35 citation statements)

References 12 publications

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“…Synthetic and to a smaller extent natural pyrochlores with a broad range of different cation substitutes have been thoroughly investigated [16,[34][35][36][37][38][39][40][41]. Gregg et al [42] observed additional Raman modes between 700 and 800 cm −1 related to U-impurities in the pyrochlore structure.…”

Section: Hementioning

confidence: 99%

“…Gregg et al [42] observed additional Raman modes between 700 and 800 cm −1 related to U-impurities in the pyrochlore structure. The annealing-induced recrystallization behavior of moderately to fully metamict, altered natural pyrochlores has been followed among others by differential thermal and thermogravimetric analysis (DTA/TG), revealing strong exothermic reactions and a noticeable weight loss [37,38,43].…”

Section: Hementioning

confidence: 99%

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Thermal annealing of natural, radiation-damaged pyrochlore

Zietlow

Beirau

Mihailova

et al. 2016

Zeitschrift Für Kristallographie - Crystalline Materials

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Radiation damage in minerals is caused by the α-decay of incorporated radionuclides, such as U and Th and their decay products. The effect of thermal annealing (400-1000 K) on radiation-damaged pyrochlores has been investigated by Raman scattering, X-ray powder diffraction (XRD), and combined differential scanning calorimetry/thermogravimetry (DSC/TG). The analysis of three natural radiation-damaged pyrochlore samples from Miass/Russia [6.4 wt% Th, 23.1 · 10 18 α-decay events per gram (dpg)], Panda Hill/Tanzania (1.6 wt% Th, 1.6 · 10 18 dpg), and Blue River/Canada (10.5 wt% U, 115.4 · 10 18 dpg), are compared with a crystalline reference pyrochlore from Schelingen (Germany). The type of structural recovery depends on the initial degree of radiation damage (Panda Hill 28 %, Blue River 85 % and Miass 100 % according to XRD), as the recrystallization temperature increases with increasing degree of amorphization. Raman spectra indicate reordering on the local scale during annealing-induced recrystallization. As Raman modes around 800 cm −1 are sensitive to radiation damage . The most radiation damaged pyrochlore (Miass) shows an abrupt recovery of both, its short-(Raman) and long-range order (X-ray) between 800 and 850 K, while the weakly damaged pyrochlore (Panda Hill) begins to recover at considerably lower temperatures (near 500 K), extending over a temperature range of ca. 300 K, up to 800 K (Raman). The pyrochlore from Blue River shows in its initial state an amorphous X-ray diffraction pattern superimposed by weak Bragg-maxima that indicates the existence of ordered regions in a damaged matrix. In contrast to the other studied pyrochlores, Raman spectra of the Blue River sample show the appearance of local modes above 560 K between 700 and 800 cm −1 resulting from its high content of U and Ta impurities. DSC measurements confirmed the observed structural recovery upon annealing. While the annealing-induced ordering of Panda Hill begins at a lower temperature (ca. 500 K) the recovery of the highly-damaged pyrochlore from Miass occurs at 800 K. The Blue-River pyrochlore shows a multi-step recovery which is similarly seen by XRD. Thermogravimetry showed a continuous mass loss on heating for all radiation-damaged pyrochlores (Panda Hill ca. 1 %, Blue River ca. 1.5 %, Miass ca. 2.9 %).

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Section: Hementioning

confidence: 99%

Section: Hementioning

confidence: 99%

Thermal annealing of natural, radiation-damaged pyrochlore

Zietlow

Beirau

Mihailova

et al. 2016

Zeitschrift Für Kristallographie - Crystalline Materials

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“…The decrease in the L-L* energy difference is associated with a change in the titanium coordination number from an octahedral (pristine region) to a tetrahedral (amorphous region) coordination [4] [24]. The correlation between the decrease of cation coordination number and amorphisation has been reported previously in studies performed by Extended X-ray Absorption Fine structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES) on similar materials [39][40] [41]. No significant change in the L-L* energy difference is observed in the partly damaged regions.…”

Section: Kr Irradiated Samplesmentioning

confidence: 75%

Krypton irradiation damage in Nd-doped zirconolite and perovskite

Davoisne

Stennett

Hyatt

et al. 2011

Journal of Nuclear Materials

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Understanding the effect of radiation damage and noble gas accommodation in potential ceramic hosts for plutonium disposition is necessary to evaluate the long-term behaviour during geological disposal. Polycrystalline samples of Nd-doped zirconolite and Nd-doped perovskite were irradiated ex-situ with 2 MeV Kr + at a dose of 5x10 15 ions.cm -2 to simulate plutonium nuclei recoil during alpha decay. The feasibility of thin section preparation of both pristine and irradiated samples by Focussed Ion Beam sectioning was demonstrated. After irradiation, the Nd-doped zirconolite revealed a well defined amorphous region separated from the pristine material by a thin (40-60 nm) damaged interface. The Nd-doped perovskite contained a defined irradiated region composed of an amorphous region surrounded by damaged regions. In both samples, as revealed by electron diffraction, the damaged regions and interface have a structure in which the fluorite sublattice is present while the pristine lattice is absent. In addition in Nddoped perovskite, the amorphisation dose depended on crystallographic orientation and possibly sample configuration (thin section and bulk). In Nd-doped perovskite, Electron Energy Loss Spectroscopy study revealed a change in Ti coordination associated with the crystal to amorphous transition.

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“…The defects along the twin boundaries may become sites at which actinide elements are incorporated. In some instances [44], there was evidence for the formation of crystals (5-100 nm) with d -spacings similar to those of the fluorite structure type. Lumpkin et al [a] suggested that metamict zirconolite may recrystallize initially with a disordered, fluorite-type structure.…”

Section: Waste Forms For Piutoniummentioning

confidence: 98%