Do dislocations act as atomic autobahns for oxygen in the perovskite oxide SrTiO₃?

Abstract

The transport properties of edge dislocations comprising a symmetrical 6° [001] tilt grain boundary in weakly acceptor-doped SrTiO3 were investigated by means of various experimental and computational techniques. Oxygen transport along the dislocation array was probed by means of (18)O/(16)O exchange experiments under (standard) oxidising conditions (pO2 = 5 × 10(-1) bar) and also under reducing conditions (pO2 = 7 × 10(-22) bar) at T = 973 K. In both cases, isotope profiles obtained by Secondary Ion Mass Spectrometry (SIMS) indicated no evidence of fast diffusion along the dislocation array. Charge transport across the dislocation array was probed in equilibrium electrical conductivity measurements as a function of oxygen partial pressure, 10(-23) ≤ pO2/bar ≤ 1 at temperatures of T/K = 950, 1050, 1100. A significant decrease in the conductivity of the bicrystal (relative to that of a single crystal) was observed under oxidising conditions, but not under reducing conditions. These studies were complemented by static lattice simulations employing empirical pair-potentials. The simulations predict, that the tilt boundary comprises two types of dislocation cores, that the formation of oxygen vacancies is energetically preferred at both cores relative to the bulk, and that the migration of oxygen ions along both cores is hindered relative to the bulk. Combining all results and literature reports, we present a comprehensive and consistent picture of the transport properties of dislocations in SrTiO3.

Atomic structure and chemistry of dislocation cores at low-angle tilt grain boundary in SrTiO3 bicrystals

“…3c, which has consistently been found from different dislocations along the boundary. This feature agrees well with the dissociated core structures proposed for the same type of edge dislocations [12,26]. Moreover, dissociation has also been found in other different types of dislocations [25,27].…”

Influence of Dislocations in Transition Metal Oxides on Selected Physical and Chemical Properties

“…By employing a concurrent atomistic continuum simulation Yang et al [95] also confirmed the importance of easy glide planes in SrTiO 3 resulting in a preference of the <110> directions for dislocation nucleation and revealed that the presence of an agglomeration of dislocations in form of bicrystalline boundaries in SrTiO 3 has a significant effect on the mechanical properties and the crack evolution [97]. Bicrystals have also been widely investigated in order to determine whether dislocations have an impact on the ionic transport of oxygen [45] or not [17]. By molecular dynamics simulations of dislocations it was found that the formation enthalpy of oxygen vacancies is significantly lower compared to the bulk [31].…”

Local crystallographic shear structures in a[201] extended mixed dislocations of SrTiO3 unraveled by atomic-scale imaging using transmission electron microscopy and spectroscopy

“…[6][7][8][9][10] In order to systematically elucidate the microstructure-property relationships in perovskite oxides, dislocations at bicrystal grain boundaries have been extensively studied. [11][12][13] This is mainly because, as model systems, the type and the density of dislocations at bicrystal grain boundaries can be controlled to a large extent by adjusting the misorientation between the two crystal parts. Strontium titanate (SrTiO 3 ) is a representative perovskite oxide and is a well-known prototype material for resistive switching.…”