Abstract
Revealing whether dislocations accelerate oxygen ion transport is important for providing abilities in tuning the ionic conductivity of ceramic materials. In this study, we report how dislocations affect oxygen ion diffusion in Sr-doped LaMnO3 (LSM), a model perovskite oxide that serves in energy conversion technologies. LSM epitaxial thin films with thicknesses ranging from 10 nm to more than 100 nm were prepared by pulsed laser deposition on single-crystal LaAlO3 and SrTiO3 substrates. The lattice mismatch between the film and substrates induces compressive or tensile in-plane strain in the LSM layers. This lattice strain is partially reduced by dislocations, especially in the LSM films on LaAlO3. Oxygen isotope exchange measured by secondary ion mass spectrometry revealed the existence of at least two very different diffusion coefficients in the LSM films on LaAlO3. The diffusion profiles can be quantitatively explained by the existence of fast oxygen ion diffusion along threading dislocations that is faster by up to 3 orders of magnitude compared to that in LSM bulk.
Highlights
Dislocations play a crucial role in many semiconductor applications and are well investigated
One study on La1−xSrxMnO3 (LSM) thin films reported a dependence of the surface exchange coefficient on the strain state of the films, with higher values in relaxed LSM layers, and this outcome was attributed to dislocations.[15]
The structure of the as-prepared LSM thin films on STO and LAO substrates with thicknesses (d) between 10 and 140 nm was investigated by X-ray diffraction (XRD), as shown in Figure 1a,d. (We denote the LSM films on STO as LSM/STO and the LSM films on LAO as LSM/LAO.) These XRD measurements indicate that the LSM films are (100) oriented
Summary
Dislocations play a crucial role in many semiconductor applications and are well investigated. We believe the effect of dislocations is two-fold: properties may change in the core, which has under-coordinated atoms and excess space, and in the zone surrounding the dislocation, which can exhibit segregation of point defects either due to the dislocation strain field[20] or due to space charge formation under the effect of the core potential.[9,11] In this contribution, we quantify the role of dislocations for oxygen ion transport in LSM epitaxial thin films. LSM is an important model of mixed ionic electronic conducting oxides and is widely studied due to its functionality as a cathode in solid oxide fuel cells (SOFCs) It has suitably high electronic conductivity but a rather low ionic conductivity.[21−23] LSM thin films were prepared on single-crystalline substrates, SrTiO3 (STO) and LaAlO3 (LAO), providing tensile and compressive strain in the films, respectively. Dislocations can provide fast pathways for accelerating oxygen ion diffusion in nanoscale LSM thin films where a high density of dislocations is achievable
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