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Amorphization of Ta 2 O 5 under swift heavy ion irradiation

Cusick, Alex B. and Lang, Maik and Zhang, Fuxiang and Sun, Kai and Li, Weixing and Kluth, Patrick and Trautmann, Christina and Ewing, Rodney C. (2017):
Amorphization of Ta 2 O 5 under swift heavy ion irradiation.
In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Elsevier Science Publishing, pp. 25-33, 407, ISSN 0168583X,
DOI: 10.1016/j.nimb.2017.05.036,
[Online-Edition: https://doi.org/10.1016/j.nimb.2017.05.036],
[Article]

Abstract

Crystalline Ta2O5 powder is shown to amorphize under 2.2 GeV 197Au ion irradiation. Synchrotron X-ray diffraction (XRD), Raman spectroscopy, small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) were used to characterize the structural transition from crystalline to fully-amorphous. Based on Rietveld refinement of XRD data, the initial structure is orthorhombic (P2mm) with a very large unit cell (a = 6.20, b = 40.29, c = 3.89 Å; V = 971.7 Å3), ideally containing 22 Ta and 55 O atoms. At a fluence of approximately 3 × 1011 ions/cm2, a diffuse amorphous background becomes evident, increasing in intensity relative to diffraction maxima until full amorphization is achieved at approximately 3 × 1012 ions/cm2. An anisotropic distortion of the orthorhombic structure occurred during the amorphization process, with an approximately constant unit cell volume. The amorphous phase fraction as a function of fluence was determined, yielding a trend that is consistent with a direct-impact model for amorphization. SAXS and TEM data indicate that ion tracks exhibit a core-shell morphology. Raman data show that the amorphous phase is comprised of TaO6 and TaO5 coordination-polyhedra in contrast to the TaO6 and TaO7 units that exist in crystalline Ta2O5. Analysis of Raman data shows that oxygen-deficiency increases with fluence, indicating a loss of oxygen that leads to an estimated final stoichiometry of Ta2O4.2 at a fluence of 1 × 1013 ions/cm2.

Item Type: Article
Erschienen: 2017
Creators: Cusick, Alex B. and Lang, Maik and Zhang, Fuxiang and Sun, Kai and Li, Weixing and Kluth, Patrick and Trautmann, Christina and Ewing, Rodney C.
Title: Amorphization of Ta 2 O 5 under swift heavy ion irradiation
Language: English
Abstract:

Crystalline Ta2O5 powder is shown to amorphize under 2.2 GeV 197Au ion irradiation. Synchrotron X-ray diffraction (XRD), Raman spectroscopy, small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) were used to characterize the structural transition from crystalline to fully-amorphous. Based on Rietveld refinement of XRD data, the initial structure is orthorhombic (P2mm) with a very large unit cell (a = 6.20, b = 40.29, c = 3.89 Å; V = 971.7 Å3), ideally containing 22 Ta and 55 O atoms. At a fluence of approximately 3 × 1011 ions/cm2, a diffuse amorphous background becomes evident, increasing in intensity relative to diffraction maxima until full amorphization is achieved at approximately 3 × 1012 ions/cm2. An anisotropic distortion of the orthorhombic structure occurred during the amorphization process, with an approximately constant unit cell volume. The amorphous phase fraction as a function of fluence was determined, yielding a trend that is consistent with a direct-impact model for amorphization. SAXS and TEM data indicate that ion tracks exhibit a core-shell morphology. Raman data show that the amorphous phase is comprised of TaO6 and TaO5 coordination-polyhedra in contrast to the TaO6 and TaO7 units that exist in crystalline Ta2O5. Analysis of Raman data shows that oxygen-deficiency increases with fluence, indicating a loss of oxygen that leads to an estimated final stoichiometry of Ta2O4.2 at a fluence of 1 × 1013 ions/cm2.

Journal or Publication Title: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
Volume: 407
Publisher: Elsevier Science Publishing
Uncontrolled Keywords: Swift heavy Ions, Irradiation, Phase Transformation, Tantalum oxide, Amorphization
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: 29 Dec 2017 12:30
DOI: 10.1016/j.nimb.2017.05.036
Official URL: https://doi.org/10.1016/j.nimb.2017.05.036
Funders: This work was supported by the Office of Basic Energy Sciences of the US-DOE under Grant DE-FG02-97ER45656; NSF COMPRES under Grant EAR01-35554; and US-DOE under Contract DE-AC02-10886., HPCAT operations are supported by DOE-NNSA under Award #DE-NA0001974 and DOE-BES under Award #DE-FG02-99ER45775, with partial instrumentation funding by NSF., We would also like to acknowledge the support of NSF grant #DMR-0723032 for access to the JEOL 3100R05 electron microscope., Part of the research was performed at the SAXS/WAXS beamline at the Australian Synchrotron., PK acknowledges the Australian Research Council for financial support.
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