Unraveling bulk and grain boundary electrical properties in La0.8Sr0.2Mn1−yO3±δ thin films

Abstract

Grain boundaries in Sr-doped LaMnO3±δ thin films have been shown to strongly influence the electronic and oxygen mass transport properties, being able to profoundly modify the nature of the material. The unique behaviour of the grain boundaries can be correlated with substantial modifications of the cation concentration at the interfaces, which can be tuned by changing the overall cationic ratio in the films. In this work, we study the electronic properties of La0.8Sr0.2Mn1-yO3±δ thin films with variable Mn content. The influence of the cationic composition on the grain boundary and grain bulk electronic properties is elucidated by studying the manganese valence state evolution using spectroscopy techniques and by confronting the electronic properties of epitaxial and polycrystalline films. Substantial differences in the electronic conduction mechanism are found in the presence of grain boundaries and depending on the manganese content. Moreover, the unique defect chemistry of the nanomaterial is elucidated by measuring the electrical resistance of the thin films as a function of oxygen partial pressure, disclosing the importance of the cationic local nonstoichiometry on the thin films behavior. † Institute of Engineering Univ. Grenoble Alpes

Visualizing local fast ionic conduction pathways in nanocrystalline lanthanum manganite by isotope exchange-atom probe tomography

“…Note that the observed strong dopant segregation is expected to have a stronger impact on the electronic conductivity and magnetic properties of LSM. [32][33][34] Overall, such ndings (and similar observations previously reported by our group for nanocrystalline lanthanum chromite) 20 call attention to the need of accurate models which capture the different driving forces for a proper description of local chemistry and relevant cation non-stoichiometry in nondilute systems. A Poisson-Cahn approach, accounting for the electrostatic, but also structural and elastic contributions in nondiluted system, could in principle provide the rationale for the observed ion accumulation at the grain boundaries.…”

Engineering Transport in Manganites by Tuning Local Nonstoichiometry in Grain Boundaries

“…This epitaxial film is expected to behave mostly like the grain interior of polycrystalline LSM 0.85 and is taken as a reference to ensure that the effects observed are associated with the GBs. Indeed, the polycrystalline and epitaxial LSM 0.85 thin films present the same bulk cationic composition, Mn oxidation state, and consequently, oxygen content . As shown in Figure c, the epitaxial LSM 0.85 film (blue open symbols) indeed presents a metal–insulator (M–I) transition typical of bulk stoichiometric manganites.…”

“…In these Mn‐rich GBs, the decrease of La is not supposed to affect the electronic transport, while the progressive increase of Mn helps to restore the metallic long‐range order, gradually improving the metallic behavior. It is worth mentioning that also an enhancement of the bulk conductivity was measured in the epitaxial thin films increasing the Mn content (see Figure S19 in the Supporting Information) . Nevertheless, the conductivity of the polycrystalline thin films is orders of magnitude lower than the corresponding epitaxial one, meaning that the GB contribution is always dominating the macroscopic electronic transport.…”

Pushing the Study of Point Defects in Thin Film Ferrites to Low Temperatures Using In Situ Ellipsometry

“…It must be noted here that the presence of high angle grain boundaries in the LSF20 thin film may locally modify the point defect concentration, as was previously found in other MIEC materials (see Section S3, Supporting Information, for the discussion about the effects of homogeneity of the thin films and its effects on the ellipsometric parameters). [ 9,35 ] Overall, it is possible to conclude that the deposited LSF layers provide a representative set of samples for the study of the defect chemistry in LSF thin films.…”