A model for electron scattering in irradiated pyrochlore-fluorite systems

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dc.contributor.authorLumpkin, GRen_AU
dc.contributor.authorBlackford, MGen_AU
dc.contributor.authorSmith, KLen_AU
dc.contributor.authorWhittle, KRen_AU
dc.contributor.authorZaluzec, NJen_AU
dc.date.accessioned2023-01-13T01:16:13Zen_AU
dc.date.available2023-01-13T01:16:13Zen_AU
dc.date.issued2009-07-26en_AU
dc.date.statistics2022-10-20en_AU
dc.description.abstractCertain minerals, materials for energy, and high technology devices may undergo irradiation, either internally through alpha decay, or externally by neutrons or ions [1]. Many of these materials become amorphous when irradiated beyond a critical dose level. Electron diffraction patterns are routinely used to study the structure of these materials, including the observation of order-disorder phenomena during irradiation [2]. Here we show how the intensities of Bragg beams change from a dynamical to a kinematic-like state during the accumulation of amorphous domains in the material. The transition from the crystalline to the amorphous state can be considered as a two-phase problem, with fc + fa = 1, where fc and fa are the fractions of the crystalline and amorphous phases, both having the same composition. For fc = 1 the perfect crystal scatters into the nodes of the reciprocal lattice according to the many-beam dynamical equations and for fa = 1 the amorphous phase scatters according to the Debye equation. Figure 1 shows the strong Bragg-Bragg interactions that occur in the perfect crystal according to relationships like (hkl)1 + (hkl)2 = (hkl)3. However, once there are sufficient amorphous domains in the material, the diffuse scattering from these domains will begin to attenuate the double diffraction relationship between Bragg beams via relationships like (hkl)1 + (am)1 = (am)2 and (am)1 + (hkl)1 = (am)2. Multiple diffuse scattering, e.g., (am)1 + (am)2 = (am)3, will eventually come into play as shown in Figure 1. Thus, the relative intensities of the Bragg beams change dramatically with increasing radiation dose as fa increases. The above model also suggests that the intensity scattered from the amorphous phase will be dependent upon the orientation of the specimen and that Bragg-diffuse interactions may be observed. We tested this model by irradiating TEM samples of Gd2Ti2O7 in the IVEM-Tandem Facility at Argonne National Laboratory using 1.0 MeV Kr ions. The top row of Figure 2 reveals a systematic change in the Bragg beam intensities of the crystalline fraction from a dynamical pattern toward a kinematic-like pattern for the [110] zone axis with increasing dose. The weaker superlattice beams are lost in the amorphous background or in the enhanced small angle scattering. As shown previously [3], kinematically strong beams always the last to disappear during irradiation. Additional dynamical scattering effects are shown in the bottom row of Figure 2, in which the specimen is tilted to a 〈111〉 systematic row. These SAED patterns exhibit stronger scattering at lower dose levels from the amorphous fraction due to the removal of numerous Bragg beams from the Ewald sphere upon tilting, together with multiple Bragg-diffuse scattering along the systematic row. Certain superlattice beams (e.g., 333) can be observed to high dose levels, indicating that the crystalline domains retain the ordered pyrochlore structure. The model provides a general description of changes in Bragg beam intensities during the crystalline-amorphous transformation, but it is especially relevant to pyrochlore-fluorite systems in which the superlattice beams are very weak in the kinematic-like state. This has major implications for the interpretation of order-disorder phenomena for different damage mechanisms. References [1] Ewing, R.C., Weber, W.J., Lian, J., J. Appl. Phys. 95, 5949-5972 (2004). [2] Lian, J., Chen, J., Wang, L.M., Ewing, R.C., Farmer, J.M., Boatner, L.A., Helean, K.B., Phys. Rev. B 68, 134107 (2003). [3] Smith, K.L., Zaluzec, N.J., Lumpkin, G.R., In situ studies of ion irradiated zirconolite, pyrochlore, and perovskite. J. Nucl. Mater. 250, 36-52 (1997). © 2009 Microscopy Society of Americaen_AU
dc.identifier.citationLumpkin, G. R., Blackford, M. G., Smith, K. L., Whittle, K. R., & Zaluzec, N. J. (2009). A model for electron scattering in irradiated pyrochlore-fluorite systems. Paper presented at Microscopy and Microanalysis 2009, Richmond, Virginia, USA, July 26 – July 30, 2009. In Microscopy and Microanalysis, 15(S2), 1358-1359. doi:10.1017/S1431927609092836en_AU
dc.identifier.conferenceenddate30 July 2009en_AU
dc.identifier.conferencenameMicroscopy and Microanalysis 2009en_AU
dc.identifier.conferenceplaceRichmond, Virginiaen_AU
dc.identifier.conferencestartdate26 July 2009en_AU
dc.identifier.issn1435-8115en_AU
dc.identifier.issueS2en_AU
dc.identifier.journaltitleMicroscopy and Microanalysisen_AU
dc.identifier.pagination1358-1359en_AU
dc.identifier.urihttps://doi.org/10.1017/S1431927609092836en_AU
dc.identifier.urihttps://apo.ansto.gov.au/dspace/handle/10238/14339en_AU
dc.identifier.volume15en_AU
dc.language.isoenen_AU
dc.publisherCambridge University Pressen_AU
dc.subjectSimulationen_AU
dc.subjectIrradiationen_AU
dc.subjectPyrochloreen_AU
dc.subjectFluoriteen_AU
dc.subjectMineralsen_AU
dc.subjectAlpha decayen_AU
dc.titleA model for electron scattering in irradiated pyrochlore-fluorite systemsen_AU
dc.typeConference Abstracten_AU
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