Browsing by Author "Guagliardo, PR"

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    Cation antisite disorder in uranium-doped gadolinium zirconate pyrochlores
    (Elsevier, 2014-09-01) Gregg, DJ; Zhang, ZM; Thorogood, GJ; Kennedy, BJ; Kimpton, JA; Griffiths, GJ; Guagliardo, PR; Lumpkin, GR; Vance, ER
    The incorporation of uranium into gadolinium zirconate (Gd2Zr2O7) is investigated by synchrotron X-ray powder diffraction and X-ray absorption near-edge structure (XANES) spectroscopy. The results suggest that the uranium cation is largely located on the pyrochlore B-site instead of the targeted A-site. Cation disorder in Gd2Zr2O7 and U-doped Gd2Zr2O7 is investigated by positron annihilation lifetime spectroscopy (PALS) which demonstrates the absence of cation vacancies in these systems. This work provides direct evidence for cation antisite (A- and B-site mixing) disorder in U-doped and off-stoichiometric Gd2Zr2O7 pyrochlore. © 2014, Elsevier B.V.
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    Positron annihilation in off-stoichiometric and ta-doped Zn2TiO4
    (John Wiley and Sons, 2013-08-08) Guagliardo, PR; Vance, ER; Lumpkin, GR; Blackford, MG; Sudarshan, K; Davis, J; Samarin, S; Williams, JF
    While Zn vacancies are regarded as the charge compensators in Ti-rich Zn2TiO4, no evidence of cation vacancies in essentially single-phase samples containing up to 13 wt% excess TiO2 was evident from positron annihilation lifetime spectroscopy (PALS). Nor was there strong evidence of cation vacancies in Ta-doped samples targeted to contain either tetrahedral or octahedral vacancies, although there was a small increase in the lifetime as the doping level increased and the structure changed from cubic to tetragonal. © 2013, The American Ceramic Society.