Enrique Ruiz-Trejo

Atomistic simulation of defects and ion migration in LaYO3

Abstract Atomistic simulation techniques have been used to investigate the energetics of defects, oxygen migration and proton incorporation in the high temperature proton conductor LaYO 3 . The interatomic potentials have reproduced the observed unit cell parameters. Defect calculations indicate that Schottky-type defects have unfavourable energies of formation. The calculation of the energies of solution for alkaline-earth dopants revealed that Sr has the highest solubility in accord with experiment. It was estimated that oxygen migration takes place via a curved route with an activation energy of 1.22 eV. The enthalpies for the incorporation of water into alkaline earth doped LaYO 3 were also calculated.

Structure, point defects and ion migration in LaInO3

Abstract This article deals with the energetics of point defects, oxygen migration and proton incorporation in LaInO3. We have used atomistic simulation methods to determine the most possible structure for this oxide and compare this result with Rietveld analysis of a sample. Defect energy calculations show that substitution of La by Sr is conducive to the production of oxygen vacancies. We have calculated the energy of oxygen migration between different oxygen sites that takes place through various paths. With the methods utilised, we also found that the incorporation of water into a LaInO3 cell is favourable being this a necessary condition for the occurrence of proton conduction in this system. These results are compared to both experimental and previous calculations and their validity is discussed.

Deuterium conductivity, diffusion and implantation in Sr-doped LaYO3

Abstract A study of deuterium conductivity and diffusion in the oxide perovskite La 0.9 Sr 0.1 YO 3− δ is presented in this work. Deuterium ions were implanted into La 0.9 Sr 0.1 YO 3− δ (50 keV, 1×10 16 atoms/cm 2 ) and the corresponding deuterium depth profile was determined by SIMS and compared with a Monte Carlo simulation (TRIM96). This implant was used as a standard for the determination of deuterium concentration in a La 0.9 Sr 0.1 YO 3− δ sample pre-treated in D 2 O atmosphere. In this way, it was fully confirmed that La 0.9 Sr 0.1 YO 3− δ incorporates water at high temperatures. The conductivity of La 0.9 Sr 0.1 YO 3− δ was measured in D 2 O atmosphere and compared with other proton (deuteron) conductors. Concentration and conductivity data were used in conjunction to estimate the deuterium diffusivity and the constant of reaction of (heavy) water incorporation into LaYO 3 . Some comments on the catalytic activity of this oxide are made.

Nanoparticles and Nanograin-Sized Y-Doped CeO2 Ceramics

In this article we discuss the synthesis of nanoparticles and the preparation of dense nanoceramics of Y-doped CeO 2 . We prepared the nanoparticles by combustion synthesis and characterized the nanopowders by X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy. The good sintering properties of these nanopowders allowed us to obtain very dense ceramics of Y-doped CeO 2 (>90% theoretical density) and keep the grain size small, in some cases around 100 nm, by using sintering temperatures as low as 1250°C and very short annealing times between 5 and 60 min. The microstructure of these nanoceramics was analyzed by atomic force microscopy and SEM. The most interesting feature of these nanoceramics is that the electrical measurements in N 2 (Po 2 = 3.5 X 10 -6 atm) carried out by the four-point dc technique showed a considerable increase in total conductivity in comparison with the measurements in air or oxygen in the range 700-900°C. This conductivity enhancement might be associated with the electronic contribution to the total conductivity and it is clearly higher than the ionic conductivity in the same temperature range.

On the superconductivity suppression in Ln1−xPrxBa2Cu3O7

Abstract The critical praseodymium concentration X c sc for superconductivity suppression in the Ln 1− x Pr x Ba 2 Cu 3 O 7 solid solutions has been determined. By means of electric resistivity and magnetic susceptibility measurements we found that for Ln = Y, Er, Sm and Gd the X c sc is 0.57, 0.60, 0.45, and 0.40 resectively. We establish a transparent correlation between this critical concentration and the ionic radii of the rare earth and the cell volume. We included in our analysis recent experimental published data on the Ln = Nd, Sm, Eu, Gd and Tm series; the trend is preserved. A volume dependent hole trapping effect stands out from these correlations. A linear trend seems to be followed by the rare earths in Ln x Pr x Ba 2 Cu 3 O 7 . We speculate about the suppression of the superconductivity in these solid solutions.