Marcela A. Taylor

Density Functional Theory (DFT) based ab-initio calculations were performed for several Zr compounds. In a first stage we compute the Electric Field Gradient (EFG) tensor at the Zr site of α-Zr using the well-established all-electron full-potential linearized augmented plane waves (FP-LAPW) method. Using the nuclear quadrupole coupling constant C Q determined at 4.2 K at the Zr site of α-Zr by means of 91 Zr-nuclear quadrupole resonance (NMR), the nuclear quadrupole moment Q of the 5/2+ ground state of 91 Zr was determined with a well-justified error bar. The obtained value, Q ( 90 Zr)=0.44(3) b is 14% smaller than those reported in the literature. The main goal of our study is to determine the capability and accuracy of the GIPAW method for computing the EFG at the Zr sites compound. We show here that the GIPAW method predicts EFG´s that are in excellent agreement with the well-trusted FP-LAPW results.

"Montmorillonite (MMT) clays are 2:1 layered structures which in natural state may allocate different hydrated cations such as M-nH2O (M= Na, Ca, Fe, etc.) in its interlayer space. Depending on the capability for ion sorption, these materials are interesting for environmental remediation. In this work we experimentally study the Co sorption in a natural Na-MMT using UV-visible spectrometry and XRD on semi-oriented samples, and then analyze the sorption ability of this clay by means of ab initio calculation performed on pristine MMT. The structural properties of Na-MMT and Co-adsorbed MMT, and the hyperfine parameters at different atomic sites were analyzed and compared with the experimental ones for the first clay. For the case of the Co-MMT, the hyperfine parameters are presented for the first time. The theoretical predictions based on total energy considerations confirm that Co incorporation replacing Na is energetically favorable. Also, the basal spacing d001 experimentally obtained is well reproduced by the ab initio calculation."

The diffusion of all stable lanthanides was measured both in calcia stabilized zirconia (CSZ) and in yttria stabilized zirconia (YSZ) in the temperature range between 1286 and 1600 °C. The lanthanide diffusion coefficients obtained increase with increasing ionic radius. The experimental activation enthalpy of diffusion is near 6 eV for CSZ and between 4 and 5 eV for YSZ and is not strongly affected by the type of lanthanide. The results were correlated with defect energy calculations of the lanthanide diffusion enthalpy using the Mott-Littleton approach. An association enthalpy of cation vacancies with oxygen vacancies of about 1 eV (96 kJ/mol) was deduced in the case of CSZ, while there is no association in the case of YSZ. Furthermore, the change in diffusion coefficients can be correlated to the interaction parameter for the interaction between the lanthanide oxide with zirconia: The higher the interaction parameter, the higher the lanthanide diffusion coefficient.