Suchergebnisse

Simulations of diffusion in solids often produce poor statistics of diffusion events. We present an analytical expression for the statistical error in ion conductivity obtained in such simulations. The error expression is not restricted to any computational method in particular, but valid in the context of simulation of Poisson processes in general. This analytical error expression is verified numerically for the case of Gd-doped ceria by running a large number of kinetic Monte Carlo calculations. ; Funding Agencies|Swedish Energy Agency (STEM) [35515-1]; Carl Tryggers Foundation [CTS 14:433]; Swedish Research Council (VR) [2014-5993, 2011-42-59]; LiLi-NFM; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-MatLiU) [2009 00971]

Sm-doped ceria is a prospective electrolyte material for intermediate-temperature solid-oxide fuel cells (IT-SOFC). Equilibrium ab initio molecular dynamics (AIMD) studies of oxygen ion diffusion in this material are currently impractical due to the rareness of diffusive events on the accessible timescale. To overcome this issue we have performed ab initio non-equilibrium molecular dynamics calculations of Sm-doped ceria using the color diffusion algorithm. Applying an external force field we have been able to increase the frequency of diffusive events over the simulation time, while keeping the physical mechanism of diffusion intact. We have investigated the temperature dependence of the maximum strength of the applied external field that could be used while maintaining the response of the system in a linear regime. This allows one to obtain the diffusivity at zero field. The bulk ionic conductivity has been calculated and found to match the experimental data well. We have also compared the description of the diffusion process by our method to previous findings and show that the migration mechanism and site preference of oxygen vacancies with respect to the Sm dopants is well reproduced. (C) 2016 Elsevier B.V. All rights reserved. ; Funding Agencies|Swedish Energy Agency (STEM) [35515-1]; Carl Tryggers Foundation [CTS 14:433]; Swedish Research Council (VR) [2014-5993, 2014-4750]; LiLi-NFM; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

A first-principles nonequilibrium molecular dynamics (NEMD) study employing the color-diffusion algorithm has been conducted to obtain the bulk ionic conductivity and the diffusion constant of gadolinium-doped cerium oxide (GDC) in the 850-1150 K temperature range. Being a slow process, ionic diffusion in solids usually requires simulation times that are prohibitively long for ab initio equilibrium molecular dynamics. The use of the color-diffusion algorithm allowed us to substantially speed up the oxygen-ion diffusion. The key parameters of the method, such as field direction and strength as well as color-charge distribution, have been investigated and their optimized values for the considered system have been determined. The calculated ionic conductivity and diffusion constants are in good agreement with available experimental data. ; Funding Agencies|Swedish Energy Agency (STEM) [355151]; Carl Tryggers Foundation [CTS 14:433]; Swedish Research Council (VR) [2014-5993, 2014-4750, 637-2013-7296]; LiLi-NFM; Swedish Government Strategic Research Area Grant in Materials Science