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Title: Vacancy–Vacancy Interaction Induced Oxygen Diffusivity Enhancement in Undoped Nonstoichiometric Ceria

Abstract

In this paper, molecular dynamics simulations and molecular static calculations have been used to systematically study oxygen vacancy transport in undoped nonstoichiometric ceria. A strong oxygen diffusivity enhancement appears in the vacancy concentration range of 2–4% over the temperature range from 1000 to 2000 K. An Arrhenius ion diffusion mechanism by vacancy hopping along the (100) direction is unambiguously identified, and an increasing trend of both the oxygen migration barrier and the prefactor with increasing vacancy concentration is observed. Within the framework of classical diffusion theory, a weak concentration dependence of the prefactor in oxygen vacancy migration is shown to be crucial for explaining the unusual fast oxygen ion migration in the low concentration range and consequently the appearance of a maximum in oxygen diffusivity. Finally, a representative (100) direction interaction model is constructed to identify long-range vacancy–vacancy interaction as the structural origin of the positive correlation between oxygen migration barrier and vacancy concentration.

Authors:
 [1];  [2];  [2]
  1. Univ. of Tennessee, Knoxville, TN (United States). Dept. of Materials Science and Engineering
  2. Univ. of Tennessee, Knoxville, TN (United States). Dept. of Materials Science and Engineering; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Contributing Org.:
Univ. of Tennessee, Knoxville, TN (United States)
OSTI Identifier:
1265538
Grant/Contract Number:
AC05-00OR22725; AC02-05CH11231
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 119; Journal Issue: 23; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE; Ceria; Vacancy; Oxygen Diffusivity

Citation Formats

Yuan, Fenglin, Zhang, Yanwen, and Weber, William J. Vacancy–Vacancy Interaction Induced Oxygen Diffusivity Enhancement in Undoped Nonstoichiometric Ceria. United States: N. p., 2015. Web. doi:10.1021/acs.jpcc.5b01317.
Yuan, Fenglin, Zhang, Yanwen, & Weber, William J. Vacancy–Vacancy Interaction Induced Oxygen Diffusivity Enhancement in Undoped Nonstoichiometric Ceria. United States. doi:10.1021/acs.jpcc.5b01317.
Yuan, Fenglin, Zhang, Yanwen, and Weber, William J. Tue . "Vacancy–Vacancy Interaction Induced Oxygen Diffusivity Enhancement in Undoped Nonstoichiometric Ceria". United States. doi:10.1021/acs.jpcc.5b01317. https://www.osti.gov/servlets/purl/1265538.
@article{osti_1265538,
title = {Vacancy–Vacancy Interaction Induced Oxygen Diffusivity Enhancement in Undoped Nonstoichiometric Ceria},
author = {Yuan, Fenglin and Zhang, Yanwen and Weber, William J.},
abstractNote = {In this paper, molecular dynamics simulations and molecular static calculations have been used to systematically study oxygen vacancy transport in undoped nonstoichiometric ceria. A strong oxygen diffusivity enhancement appears in the vacancy concentration range of 2–4% over the temperature range from 1000 to 2000 K. An Arrhenius ion diffusion mechanism by vacancy hopping along the (100) direction is unambiguously identified, and an increasing trend of both the oxygen migration barrier and the prefactor with increasing vacancy concentration is observed. Within the framework of classical diffusion theory, a weak concentration dependence of the prefactor in oxygen vacancy migration is shown to be crucial for explaining the unusual fast oxygen ion migration in the low concentration range and consequently the appearance of a maximum in oxygen diffusivity. Finally, a representative (100) direction interaction model is constructed to identify long-range vacancy–vacancy interaction as the structural origin of the positive correlation between oxygen migration barrier and vacancy concentration.},
doi = {10.1021/acs.jpcc.5b01317},
journal = {Journal of Physical Chemistry. C},
number = 23,
volume = 119,
place = {United States},
year = {Tue May 19 00:00:00 EDT 2015},
month = {Tue May 19 00:00:00 EDT 2015}
}

Journal Article:
Free Publicly Available Full Text
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Cited by: 5works
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  • The structural properties of anion deficient ceria, CeO{sub 2-{delta}}, have been studied as a function of oxygen partial pressure, p(O{sub 2}), over the range 0>=log{sub 10p}(O{sub 2})>=-18.9 at 1273(2) K using the neutron powder diffraction technique. Rietveld refinement of the diffraction data collected on decreasing p(O{sub 2}) showed increases in the cubic lattice parameter, a, the oxygen nonstoichiometry, delta, and the isotropic thermal vibration parameters, u{sub Ce} and u{sub O}, starting at log{sub 10p}(O{sub 2}){approx}-11. The increases are continuous, but show a distinct kink at log{sub 10p}(O{sub 2}){approx}-14.5. Analysis of the total scattering (Bragg plus diffuse components) using reverse Montemore » Carlo (RMC) modelling indicates that the O{sup 2-} vacancies preferentially align as pairs in the <111> cubic directions as the degree of nonstoichiometry increases. This behaviour is discussed with reference to the chemical crystallography of the CeO{sub 2}-Ce{sub 2}O{sub 3} system at ambient temperature and, in particular, to the nature of the long-range ordering of O{sup 2-} vacancies within the crystal structure of Ce{sub 7}O{sub 12}. - Graphical abstract: Partial radial distribution function for oxygen vacancies within CeO{sub 1.710} at 1273 K (solid line) showing the increased tendency for local ordering in <111> directions compared to a random distribution (dashed line).« less
  • Kinetic lattice Monte Carlo (KLMC) model is developed for investigating oxygen vacancy diffusion in praseodymium-doped ceria. The current approach uses a database of activation energies for oxygen vacancy migration, calculated using first-principles, for various migration pathways in praseodymium-doped ceria. Since the first-principles calculations revealed significant vacancy-vacancy repulsion, we investigate the importance of that effect by conducting simulations with and without a repulsive interaction. Initially, as dopant concentrations increase, vacancy concentration and thus conductivity increases. However, at higher concentrations, vacancies interfere and repel one another, and dopants trap vacancies, creating a 'traffic jam' that decreases conductivity, which is consistent with themore » experimental findings. The modeled effective activation energy for vacancy migration slightly increased with increasing dopant concentration in qualitative agreement with the experiment. The current methodology comprising a blend of first-principle calculations and KLMC model provides a very powerful fundamental tool for predicting the optimal dopant concentration in ceria related materials. -- graphical abstract: Ionic conductivity in praseodymium doped ceria as a function of dopant concentration calculated using the kinetic lattice Monte Carlo vacancy-repelling model, which predicts the optimal composition for achieving maximum conductivity. Display Omitted Research highlights: {yields} KLMC method calculates the accurate time-dependent diffusion of oxygen vacancies. {yields} KLMC-VR model predicts a dopant concentration of {approx}15-20% to be optimal in PDC. {yields} At higher dopant concentration, vacancies interfere and repel one another, and dopants trap vacancies. {yields} Activation energy for vacancy migration increases as a function of dopant content« less