Structural response of titanate pyrochlores to swift heavy ion irradiation

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• 作者：Jacob Shamblin^a ; ^b ; Cameron L. Tracy^c ; Rodney C. Ewing^c ; Fuxiang Zhang^d ; Weixing Li^e ; Christina Trautmann^f ; ^g ; Maik Lang^a ; ^{mlang2@utk.edu" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Pyrochlore ; Amorphization ; Nuclear waste ; Swift heavy ions ; Track formation
• 刊名：Acta Materialia
• 出版年：2016
• 出版时间：15 September 2016
• 年：2016
• 卷：117
• 期：Complete
• 页码：207-215
• 全文大小：1678 K

文摘

The structure, size, and morphology of ion tracks resulting from irradiation of five different pyrochlore compositions (A₂Ti₂O₇, A = Yb, Er, Y, Gd, Sm) with 2.2 GeV ¹⁹⁷Au ions were investigated by means of synchrotron X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Radiation-induced amorphization occurred in all five materials analyzed following an exponential rate as a function of ion fluence. XRD patterns showed a general trend of increasing susceptibility of amorphization with increasing ratio of A- to B-site cation ionic radii (r_A/r_B) with the exception of Y₂Ti₂O₇ and Sm₂Ti₂O₇. This indicates that the track size does not necessarily increase with r_A/r_B, in contrast with results from previous swift heavy ion studies on Gd₂Zr_2-xTi_xO₇ pyrochlore materials. For Y₂Ti₂O₇, this effect is attributed to the significantly lower electron density of this material relative to the lanthanide-bearing pyrochlores, thus lowering the electronic energy loss (dE/dx) of the high-energy ions in this composition. An energy loss normalization procedure was performed which reveals an initial increase of amorphous track size with r_A/r_B that saturates above a cation radius ratio larger than Gd₂Ti₂O₇. This is in agreement with previous low-energy ion irradiation experiments and first principles calculations of the disordering energy of titanate pyrochlores indicating that the same trends in disordering energy apply to radiation damage induced in both the nuclear and electronic energy loss regimes. HRTEM images indicate that single ion tracks in Yb₂Ti₂O₇ and Er₂Ti₂O₇, which have small A-site cations and low r_A/r_B, exhibit a core-shell structure with a small amorphous core surrounded by a larger disordered shell. In contrast, single tracks in Gd₂Ti₂O₇ and Sm₂Ti₂O₇, have a larger amorphous core with minimal disordered shells.