skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Disorder-induced transition from grain boundary to bulk dominated ionic diffusion in pyrochlores

Abstract

In this paper, we use molecular dynamics simulations to investigate the role of grain boundaries (GBs) on ionic diffusion in pyrochlores, as a function of the GB type, chemistry of the compound, and level of cation disorder. We observe that the presence of GBs promotes oxygen transport in ordered and low-disordered systems, as the GBs are found to have a higher concentration of mobile carriers with higher mobilities than in the bulk. Thus, in ordered samples, the ionic diffusion is 2D, localized along the grain boundary. When cation disorder is introduced, bulk carriers begin to contribute to the overall diffusion, while the GB contribution is only slightly enhanced. In highly disordered samples, the diffusive behavior at the GBs is bulk-like, and the two contributions (bulk vs. GB) can no longer be distinguished. There is thus a transition from 2D/GB dominated oxygen diffusivity to 3D/bulk dominated diffusivity versus disorder in pyrochlores. Finally, these results provide new insights into the possibility of using internal interfaces to enhance ionic conductivity in nanostructured complex oxides.

Authors:
ORCiD logo [1];  [1]; ORCiD logo [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1402631
Report Number(s):
LA-UR-17-23205
Journal ID: ISSN 2040-3364; TRN: US1703116
Grant/Contract Number:
AC52-06NA25396
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nanoscale
Additional Journal Information:
Journal Volume: 9; Journal Issue: 20; Journal ID: ISSN 2040-3364
Publisher:
Royal Society of Chemistry
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Perriot, Romain, Dholabhai, Pratik P., and Uberuaga, Blas P.. Disorder-induced transition from grain boundary to bulk dominated ionic diffusion in pyrochlores. United States: N. p., 2017. Web. doi:10.1039/C7NR01373F.
Perriot, Romain, Dholabhai, Pratik P., & Uberuaga, Blas P.. Disorder-induced transition from grain boundary to bulk dominated ionic diffusion in pyrochlores. United States. doi:10.1039/C7NR01373F.
Perriot, Romain, Dholabhai, Pratik P., and Uberuaga, Blas P.. Thu . "Disorder-induced transition from grain boundary to bulk dominated ionic diffusion in pyrochlores". United States. doi:10.1039/C7NR01373F. https://www.osti.gov/servlets/purl/1402631.
@article{osti_1402631,
title = {Disorder-induced transition from grain boundary to bulk dominated ionic diffusion in pyrochlores},
author = {Perriot, Romain and Dholabhai, Pratik P. and Uberuaga, Blas P.},
abstractNote = {In this paper, we use molecular dynamics simulations to investigate the role of grain boundaries (GBs) on ionic diffusion in pyrochlores, as a function of the GB type, chemistry of the compound, and level of cation disorder. We observe that the presence of GBs promotes oxygen transport in ordered and low-disordered systems, as the GBs are found to have a higher concentration of mobile carriers with higher mobilities than in the bulk. Thus, in ordered samples, the ionic diffusion is 2D, localized along the grain boundary. When cation disorder is introduced, bulk carriers begin to contribute to the overall diffusion, while the GB contribution is only slightly enhanced. In highly disordered samples, the diffusive behavior at the GBs is bulk-like, and the two contributions (bulk vs. GB) can no longer be distinguished. There is thus a transition from 2D/GB dominated oxygen diffusivity to 3D/bulk dominated diffusivity versus disorder in pyrochlores. Finally, these results provide new insights into the possibility of using internal interfaces to enhance ionic conductivity in nanostructured complex oxides.},
doi = {10.1039/C7NR01373F},
journal = {Nanoscale},
number = 20,
volume = 9,
place = {United States},
year = {Thu May 04 00:00:00 EDT 2017},
month = {Thu May 04 00:00:00 EDT 2017}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Save / Share:
  • An illustration of the diffusion of potassium through the bulk and along the grain boundaries of PMO.
  • In the present work the authors investigate both diffusion induced grain boundary migration and grain boundary chemical diffusion in the Au/Ag system at an unusually low temperature, i.e., at room temperature. At this temperature the diffusion distance in the lattice during all experiments is very much smaller than an atomic jump distance, i.e., smaller by a factor of at least 10{sup 4}. Lattice diffusion is therefore completely frozen out. Nevertheless, the authors find that measurable DIGM occurs. The current models (at least in their present form) cannot explain these results, and some discussion is devoted to this result.
  • The purpose of this paper is to examine the microscopic nature of the contact angles that dissociated boundary segments make with undissociated boundary segments in grain boundaries which have undergone DIGM. Ig local equilibrium exists at these grain boundary intersections, this study will reveal information about the nature of the driving force for grain boundary dissociation during DIGM. Evidence will then be presented which suggests that an applied stress can result in grain boundary migration and dissociation in a manner analogous to that observed during DIGM.
  • We use molecular dynamics simulations to investigate the role of cation disorder on oxygen diffusion in Gd 2Zr 2O 7 (GZO) and Gd 2Ti 2O 7 (GTO) pyrochlores, a class of complex oxides which contain a structural vacancy relative to the basic fluorite structure. The introduction of disorder has distinct effects depending on the chemistry of the material, increasing the mobility of structural carriers by up to four orders of magnitude in GZO. In contrast, in GTO, there is no mobility at zero or low disorder on the ns timescale, but higher disorder liberates the otherwise immobile carriers, allowing diffusionmore » with rates comparable to GZO for the fully disordered material. Here, we show that the cation disorder enhances the diffusivity by both increasing the concentration of mobile structural carriers and their individual mobility. The disorder also influences the diffusion in materials containing intrinsic carriers, such as additional vacancies VO or oxygen interstitials OI. And while in ordered GZO and GTO the contribution of the intrinsic carriers dominates the overall diffusion of oxygen, OI in GZO contributes along with structural carriers, and the total diffusion rate can be calculated by assuming simple additive contributions from the two sources. Although the disorder in the materials with intrinsic defects usually enhances the diffusivity as in the defect-free case, in low concentrations, cation antisites AB or BA, where A = Gd and B = Zr or Ti, can act as traps for fast intrinsic defects. The trapping results in a lowering of the diffusivity, and causes a non-monotonic behavior of the diffusivity with disorder. Conversely, in the case of slow intrinsic defects, the main effect of the disorder is to liberate the structural carriers, resulting in an increase of the diffusivity regardless of the defect trapping.« less
  • Ionic liquid gating has a number of advantages over solid-state gating, especially for flexible or transparent devices and for applications requiring high carrier densities. But, the large number of charged ions near the channel inevitably results in Coulomb scattering, which limits the carrier mobility in otherwise clean systems. We develop a model for this Coulomb scattering. We then validate our model experimentally using ionic liquid gating of graphene across varying thicknesses of hexagonal boron nitride, demonstrating that disorder in the bulk ionic liquid often dominates the scattering.