Order-to-disorder transformation in d-phase Sc 4 Zr 3 O 12 induced by light ion irradiation
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Yongqiang Wang, Ming Tang, Jonghan Won, James A. Valdez, and Kurt E. Sickafus Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (Received 9 June 2009; accepted 8 October 2009)
Polycrystalline d-phase Sc4Zr3O12 was irradiated with 200 keV Ne+ ions at cryogenic temperature to fluences ranging from 2 1018 to 1 1021 Ne/m2. Irradiation-induced structural evolution was examined by using grazing incidence x-ray diffraction and crosssectional transmission electron microscopy. An order-to-disorder (O-D) crystal structure transformation (from an ordered d-phase to a disordered, fluorite phase) was observed to initiate by a fluence of 2 1018 Ne/m2, corresponding to a peak ballistic damage dose of 0.075 displacements per atom. This displacement damage dose is much lower than the O-D transformation dose threshold found in previous heavy ion irradiation experiments on d-Sc4Zr3O12 [J.A. Valdez et al., Nucl. Instrum. Methods B 250, 148 (2006); K.E. Sickafus et al., Nat. Mater. 6, 217 (2007)]. In this study, we contrast the O-D transformation efficiency of the light Ne ions used in these experiments, to the heavy (Kr) ions used previously, and interpret the differences in terms of enhanced damage efficiency for light ions (greater fraction of surviving defects per defect produced). To better quantify this surviving defect phenomenon, we also present new, additional ion irradiation results on d-Sc4Zr3O12, obtained from 300 keV Kr2+ and 100 keV He+ ion irradiation experiments. I. INTRODUCTION
Crystalline oxides with structures related to fluorite (CaF2) have received considerable attention as potential nuclear fuel forms1,2 and waste forms.3 In certain fluorite derivative structures, it has been shown that structural stability under irradiation is highly dependent on compound composition. For instance, in A2B2O7 pyrochlore oxides (where A and B are metal cations and O are oxygen anions), compounds with B = Ti were found to be far more susceptible to radiation-induced amorphization than those with B = Zr.4,5 In addition, A4B3O12 fluorite derivative oxides known as delta (d) phases have been tested for radiation stability, and, so far, no “4:3:12” d-phase compounds have exhibited irradiation-induced amorphization susceptibility.6 However, d-phase compounds do undergo order-to-disorder (O-D) transformations when exposed to high fluence, heavy ion irradiation.6,7 In particular, d-Sc4Zr3O12 has been shown to undergo an O-D transformation after 300 keV Kr2+ ion irradiation (cryogenic temperature) to an ion fluence a)
Address all correspondence to this author. e-mail: [email protected]; [email protected] DOI: 10.1557/JMR.2010.0027
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J. Mater. Res., Vol. 25, No. 2, Feb 2010 Downloaded: 04 Apr 2015
between 1 and 3 1020 Kr/m2 (the ballistic damage dose in this fluence range was estimated to be 23–70 displacements per atom or dpa).7 The purpose of the study presented here is to test for possible “spectrum” effects in d-Sc4Zr3O12, by irradiatin
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