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Amorphization of Ta 2 O 5 under swift heavy ion irradiation

Cusick, Alex B. ; Lang, Maik ; Zhang, Fuxiang ; Sun, Kai ; Li, Weixing ; Kluth, Patrick ; Trautmann, Christina ; 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, 407, pp. 25-33. Elsevier Science Publishing, ISSN 0168583X,
DOI: 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. ; Lang, Maik ; Zhang, Fuxiang ; Sun, Kai ; Li, Weixing ; Kluth, Patrick ; Trautmann, Christina ; 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
Journal 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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