The Intrinsic Structural Resistance of a Grain Boundary to Transverse Ionic Conduction

Abstract

Ion transport across grain boundaries in diverse polycrystalline ionic conductors is often found to be hindered. Such behaviour is commonly attributed to the presence of a highly resistive second phase or to the presence of space‐charge zones, in which mobile charge carriers are strongly depleted. One other possible cause – the severe perturbation of the crystal structure within the grain‐boundary core – is widely ignored. Employing molecular dynamics (MD) simulations of the model Σ5(310)[001] grain boundary in fluorite‐structured CeO2, we demonstrate an approach to extract the intrinsic structural resistance of a grain boundary (to ionic transport across it), and we determine this excess resistance as a function of temperature. Compared with space‐charge resistances predicted for a dilute solution of charge carriers the structural resistance of this interface is orders of magnitude smaller at temperatures below T≈1000 K but at T>1200 K it is no longer negligible.

Emergent ionic conduction in aliovalently-doped fast ion conductors

“…Previous computational studies have used a similar range of electric elds (∼0.1-30 MV cm −1 ). [30][31][32][33][34][35][36] Electric elds as large as 10 MV cm −1 are typical near interfaces, grain boundaries and in the electric double layer region. [46][47][48][49][50][51][52][53] For the ionic conduction measurement (Section 2.1), the periodic box is divided into 98 bins or layers along the x-axis for collection of statistics as shown in Fig.…”

“…While solving the equation of motion, the force due to external eld is added to the interactions between the charged ionsthe latter is calculated using a classical interatomic potential. MD studies in the absence 20,21,24,27,29 and presence of an electric eld (∼0.1-30 MV cm −1 ) [30][31][32][33][34][35][36] have been reported. For any ionic material, the application of an electric eld alters the underlying potential energy landscape.…”

Atomistic calculations of charged point defects at grain boundaries in SrTiO3

“…Note that such electrostatic artifacts are not expected to exist in more symmetric GB structures which have either a glidemirror or a screw-rotation symmetry (non-broken mirror symmetries) [16,17], as e.g. those investigated by Genreith-Schriever et al [18]. However, even though one would expect them to be present, internal electric potentials in simulation cells were not addressed in previous classical atomistic-simulation studies similar to the present work, which deal with GBs without the aforementioned symmetric properties [8,19].…”

Oxygen Diffusion in Ceramic Mixed Conducting La0.6Sr0.4Co0.2Fe0.8O3−δ : The Role of Grain and Twin Boundaries

“…It is important to distinguish between transverse and parallel directions. Grain boundaries have been known to be blocking to transverse oxygen transport in polycrystalline electrolyte materials due to space charge and impurity effects 7,10,12,21,42,43 and a direct observation of this effect has been observed through oxygen diffusion measurements in yttria doped zirconia. [44][45][46] 37 3.…”

“…All these interfaces can play a dominant role in overall device performance, however as lower temperature operation is increasingly of interest, the role played by grain boundaries is receiving more scrutiny. 2,[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Hence an understanding of grain boundary transport in polycrystalline MEIC materials, both of cations 23 and anions (oxygen ions), is becoming necessary. Understanding cation transport is relevant to segregation and degradation effects over the very long timescales necessary for operation and during high temperature processing.…”