Faster Diffusion of Oxygen Along Dislocations in (La,Sr)MnO_3+δ Is a Space‐Charge Phenomenon

Abstract

In displaying accelerated oxygen diffusion along extended defects, (La,Sr)MnO 3+δ is an atypical acceptor-doped perovskite-type oxide. In this study, 18 O/ 16 O diffusion experiments on epitaxial thin films of La 0.8 Sr 0.2 MnO 3+δ and molecular dynamics (MD) simulations are combined to elucidate the origin of this phenomenon for dislocations: Does diffusion occur along dislocation cores or along space-charge tubes? Transmission electron microscopy studies of the films revealed dislocations extending from the surface. 18 O penetration profiles measured by secondary ion mass spectrometry indicated (slow) bulk diffusion and faster diffusion along dislocations. Oxygen tracer diffusivities obtained for temperatures 873 ≤ T [K] ≤ 973were over two orders of magnitude higher for dislocations than for the bulk. The activation enthalpy of oxygen diffusion along dislocations, of (2.95 ± 0.21) eV, is surprisingly high relative to that for bulk diffusion, (2.67 ± 0.13) eV. This result militates against fast diffusion along dislocation cores. MD simulations confirmed no accelerated migration of oxide ions along dislocation cores. Faster diffusion of oxygen along dislocations in La 0.8 Sr 0.2 MnO 3+δ is thus concluded to occur within space-charge tubes in which oxygen vacancies are strongly accumulated. Reasons for and the consequences of space-charge zones at extended defects in manganite perovskites are discussed.

Structural Defects Improve the Memristive Characteristics of Epitaxial La0.8Sr0.2MnO3‐Based Devices

“…On the other hand, during LRS SET process, the re-incorporation of oxygen and drift within LSM might be limited for the LSM/STO devices due to the high quality of the epitaxial LSM film, which does not present many extended defects (Figure 10b-c). [28,29,31] Eventually, the concentration of oxygen in TiOx and oxygen vacancies in LSM/STO will increase with cycles raising the total resistance of the device. of the half-loops dislocations present in LSM/LAO films, in agreement to reference.…”

“…[30,31] Thus, thin-film engineering has emerged as a key strategy to tune functional properties to improve performance in devices such as solid oxide fuel cells [30,31] and memristive devices. [29,32] Table 1 summarizes selected relevant studies where different mechanisms were proposed for LSM-x (x = 20%-33%) memristive devices using different electrodes or by direct contact with the biased probe. Whereas several mechanisms are suggested, many of them rely on oxygen (vacancy) drift to induce the resistance change.…”

The impact of Mn nonstoichiometry on the oxygen mass transport properties of La0.8Sr0.2Mn y O3±δ thin films

“…The model correctly reproduces the main features of the profiles except for the long tails, where a small but systematic difference in the tracer fraction was observed. This behavior is commonly explained in LSM thin films by the presence of dislocations or other types of 2D structural defects, which are known to provide a preferential pathway for oxygen diffusion in manganite perovskites, allowing the tracer to diffuse more deeply into the sample [27,46]. In order to improve the fittings and to avoid uncertainties on the bulk coefficients, 2D FEM simulations based on previous works on fast diffusion in dislocations and grain boundaries were implemented [24,38,46,56].…”

“…Moreover, this local nostoichiometry can be tuned by the overall Mn/(La + Sr) ratio in the layers, offering a way to further enhance its electrochemical properties for large Mn deficiencies [Mn/(La + Sr)<0.9]. Also, faster oxygen transport along dislocations was recently proposed to originate from an accumulation of (negative) cation vacancies at the dislocation core, giving rise to a space charge accumulation of (positive) oxygen vacancies, and thus boosting the oxygen diffusivity [27]. Indeed, cation defects have been experimentally observed near the strained region of the dislocations [28].…”

Enhanced Photoconductivity at Dislocations in SrTiO3

“…Dislocation cores with their attendant space charge regions and strain fields can provide enhanced functional properties, [8] such as ionic or electronic conductivity, [9,10] oxygen diffusion, [11,12] and enable new functionalities. [13,14] Very recent advancements highlight the control of polarization by mechanical dislocation imprint in piezoelectric ceramics [15] and creation of low-dimensional superconductivity in SrTiO 3 single crystals.…”