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Response of Gd2Ti2O7 and La2Ti2O7 to swift-heavy ion irradiation and annealing

Park, Sulgiye and Lang, Maik and Tracy, Cameron L. and Zhang, Jiaming and Zhang, Fuxiang and Trautmann, Christina and Rodriguez, Matias D. and Kluth, Patrick and Ewing, Rodney C. (2015):
Response of Gd2Ti2O7 and La2Ti2O7 to swift-heavy ion irradiation and annealing.
In: Acta Materialia, Elsevier Science Publishing, pp. 1-11, 93, ISSN 13596454, [Online-Edition: http://dx.doi.org/10.1016/j.actamat.2015.04.010],
[Article]

Abstract

Swift heavy ion (2 GeV 181Ta) irradiation-induced amorphization and temperature-induced recrystallization of cubic pyrochlore Gd2Ti2O7 (View the MathML sourceFd3¯m) are compared with the response of a compositionally-similar material with a monoclinic-layered perovskite-type structure, La2Ti2O7 (P21). The averaged electronic energy loss, dE/dx, was 37 keV/nm and 35 keV/nm in Gd2Ti2O7 and La2Ti2O7, respectively. Systematic analysis of the structural modifications was completed using transmission electron microscopy, synchrotron X-ray diffraction, Raman spectroscopy, and small-angle X-ray scattering. Increasing ion-induced amorphization with increasing ion fluence was evident in the X-ray diffraction patterns of both compositions by a reduction in the intensity of the diffraction maxima concurrent with the growth in intensity of a broad diffuse scattering halo. Transmission electron microscopy analysis showed complete amorphization within ion tracks (diameter: ∼10 nm) for the perovskite-type material; whereas a concentric, core–shell morphology was evident in the ion tracks of the pyrochlore, with an outer shell of disordered yet still crystalline material with the fluorite structure surrounding an amorphous track core (diameter: ∼9 nm). The radiation response of both titanate oxides with the same stoichiometry can be understood in terms of differences in their structures and compositions. While the radiation damage susceptibility of pyrochlore A2B2O7 materials decreases as a function of the cation radius ratio rA/rB, the current study correlates this behavior with the stability field of monoclinic structures, where rLa/rTi > rGd/rTi. Isochronal annealing experiments of the irradiated materials showed complete recrystallization of La2Ti2O7 at 775 °C and of Gd2Ti2O7 at 850 °C. The annealing behavior is discussed in terms of enhanced damage recovery in La2Ti2O7, compared to the pyrochlore compounds Gd2Ti2O7. The difference in the recrystallization behavior may be related to structural constraints, i.e., reconstructing a low symmetry versus a high symmetry phase.

Item Type: Article
Erschienen: 2015
Creators: Park, Sulgiye and Lang, Maik and Tracy, Cameron L. and Zhang, Jiaming and Zhang, Fuxiang and Trautmann, Christina and Rodriguez, Matias D. and Kluth, Patrick and Ewing, Rodney C.
Title: Response of Gd2Ti2O7 and La2Ti2O7 to swift-heavy ion irradiation and annealing
Language: English
Abstract:

Swift heavy ion (2 GeV 181Ta) irradiation-induced amorphization and temperature-induced recrystallization of cubic pyrochlore Gd2Ti2O7 (View the MathML sourceFd3¯m) are compared with the response of a compositionally-similar material with a monoclinic-layered perovskite-type structure, La2Ti2O7 (P21). The averaged electronic energy loss, dE/dx, was 37 keV/nm and 35 keV/nm in Gd2Ti2O7 and La2Ti2O7, respectively. Systematic analysis of the structural modifications was completed using transmission electron microscopy, synchrotron X-ray diffraction, Raman spectroscopy, and small-angle X-ray scattering. Increasing ion-induced amorphization with increasing ion fluence was evident in the X-ray diffraction patterns of both compositions by a reduction in the intensity of the diffraction maxima concurrent with the growth in intensity of a broad diffuse scattering halo. Transmission electron microscopy analysis showed complete amorphization within ion tracks (diameter: ∼10 nm) for the perovskite-type material; whereas a concentric, core–shell morphology was evident in the ion tracks of the pyrochlore, with an outer shell of disordered yet still crystalline material with the fluorite structure surrounding an amorphous track core (diameter: ∼9 nm). The radiation response of both titanate oxides with the same stoichiometry can be understood in terms of differences in their structures and compositions. While the radiation damage susceptibility of pyrochlore A2B2O7 materials decreases as a function of the cation radius ratio rA/rB, the current study correlates this behavior with the stability field of monoclinic structures, where rLa/rTi > rGd/rTi. Isochronal annealing experiments of the irradiated materials showed complete recrystallization of La2Ti2O7 at 775 °C and of Gd2Ti2O7 at 850 °C. The annealing behavior is discussed in terms of enhanced damage recovery in La2Ti2O7, compared to the pyrochlore compounds Gd2Ti2O7. The difference in the recrystallization behavior may be related to structural constraints, i.e., reconstructing a low symmetry versus a high symmetry phase.

Journal or Publication Title: Acta Materialia
Volume: 93
Publisher: Elsevier Science Publishing
Uncontrolled Keywords: Pyrochlores, Perovskites, Swift heavy ion, Annealing, X-ray diffraction
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Ion-Beam-Modified Materials
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 02 Jul 2015 09:01
Official URL: http://dx.doi.org/10.1016/j.actamat.2015.04.010
Identification Number: doi:10.1016/j.actamat.2015.04.010
Funders: This material is based upon work supported by the US Department of Energy Office of Science, Office of Basic Energy Sciences Energy Frontier Research Center program, Materials Science of Actinides, under Award Number DE-SC0001089., SGYP acknowledges a graduate fellowship from Stanford University., The use of CHESS beam is supported by NSF & NIH/NIGMS via NSF award DMR-0225180., The Electron Micro-beam Analysis Laboratory at the University of Michigan is supported by NSF Grants DMR-987177 and DMR-0723032., PK acknowledges the Australian Research Council for financial support.
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