Browsing by Author "Ren, CL"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Ion beam irradiation of ABO4 compounds with the fergusonite, monazite, scheelite, and zircon structures
    (https://doi.org/10.1111/jace.17288, 2020-06-04) de los Reyes, M; Aughterson, RD; Gregg, DJ; Middleburgh, SC; Zaluzec, NJ; Huai, P; Ren, CL; Lumpkin, GR
    The effects of irradiation on CaWO4, SrWO4, BaWO4, YVO4, LaVO4, YNbO4, and LaNbO4 were investigated on thin crystals using 1.0 MeV Kr ions at 50‐1000 K. All of the ABO4 compounds can be amorphized with calculated damage cross sections (σa = 1/Fc0) in the range of ~0.30‐1.09 × 10‐14 cm2 ion−1 at zero Kelvin. The analysis of fluence‐temperature data returned critical temperatures for amorphization (Tc) of 311 ± 1, 358 ± 90, 325 ± 19, 415 ± 17, 541 ± 6, 636 ± 26, and 1012 ± 1 K, respectively, for the compounds listed above. Compared with previous in situ irradiation of ABO4 orthophosphate samples using 0.8 MeV Kr ions, the Tc values of LaVO4 and YVO4 are higher than those of LaPO4 and YPO4 by 82 K and 124 K, respectively. The Tc values of the three scheelite structures, CaWO4, SrWO4, and BaWO4, indicate that they are the most radiation tolerant compounds under these conditions. The A‐B cation anti‐site energies, EfAB, determined by DFT range from 2.48 to 10.58 eV and are highly correlated with the A‐B cation ionic radius ratio, rA/rB, but are not correlated with Tc across the different structure types, suggesting that the formation and migration energies of Frenkel defects play a more important role in damage recovery in these compounds. We also discuss the role of cation and anion charge/iconicity as determined by DFT. ABO4 compounds with the zircon structure and B = P or V have a distinct advantage over those with B = Si as the damaged regions do not appear to be significantly affected by polymerization of (PO4)3− or (VO4)3− groups which might stabilize the amorphous fraction and ultimately lead to phase separation as observed in zircon (ZrSiO4). © 1999-2020 John Wiley & Sons, Inc.
  • No Thumbnail Available
    Item
    Transmutation of ABO4 compounds incorporating technetium-99 and caesium-137
    (IOP Publishing, 2017-01-13) Kuo, EY; Qin, MJ; Thorogood, GJ; Huai, P; Ren, CL; Lumpkin, GR; Middleburgh, SC
    The stability of a series of ABO4ABO4 minerals incorporating radioactive 99Tc99Tc during the latter’s β-decay to 99Ru99Ru was investigated theoretically using density functional theory (DFT) computations. The compounds investigated were KTcO4KTcO4, RbTcO4RbTcO4 and CsTcO4CsTcO4. The stability of the latter, CsTcO4CsTcO4, during transmutation, when the caesium consists of the radioactive isotope 137Cs137Cs, was also investigated. For each of the compounds, two similar possible crystal structure types—scheelite and pseudoscheelite—were considered. As the 99Tc99Tc decays, or the 137Cs137Cs decays to 137Ba137Ba, reaction enthalpies were calculated for possible decompositions or precipitations of the transmuting compounds. All the possible decompositions or precipitations investigated had positive reaction enthalpies, suggesting that the transmuting compounds are all chemically stable. Volume and lattice parameter changes, however, suggest that KTcO4KTcO4 would also be structurally stable during transmutation to KRuO4KRuO4, but that CsTcO4CsTcO4 would not be structurally stable during its transmutation to BaRuO4BaRuO4. © 2017 IOP Publishing Ltd.