Investigation of surface segregation and cation diffusion of (La0.8Sr0.2)0.95Cr0.5Fe0.5O3-d
File(s)
Author(s)
Xu, Jingdong
Type
Thesis
Abstract
In the background of increasing global demand for electricity, together with dependence on conventional energy, the solid oxide fuel cell is a novel choice for the transition toward a clean and sustainable future. Working at approximately 800°C, cathode of mixed ionic and electronic conductivity enables SOFC with promising high energy efficiency. However, performance loss resulting from degradation of cathode is becoming one of the major challenges.
In this doctoral research, a model MIEC perovskite oxide, (La0.8Sr0.2)0.95Cr0.5Fe0.5O3-d (LSCrF8255) has been investigated. Secondary ion mass spectrometry (SIMS) was performed to examine the high-temperature surface behavior under various thermal histories. In addition, a series of diffusion couples were fabricated, covering cathode-electrolyte and composite cathode. Characterization provided insight into cation diffusion and interfacial evolution.
Regarding high-temperature surface behavior, it was demonstrated that temperature was the dominant factor governing A-site enrichment, while B-site cation was influenced by surface rearrangement and demixing. Under oxygen-deficient atmosphere, it was observed that at lower temperature led to more severe Sr segregation compared to oxidizing condition. The difference gradually diminished with increasing temperature. Also, Sr segregation exhibited a saturation effect due to limited availability on surface sites. The kinetics of Sr segregation revealed strong dependence on oxygen partial pressure, with the activation energy reduced by approximately 0.6 eV under oxygen-deficient atmosphere.
In terms of interfacial evolution, the GDC–LSCrF and LSGM–LSCrF diffusion couples exhibited strong interdiffusion at elevated temperature. The activation energy of bulk diffusion was approximately 2 eV, while grain boundary diffusion was 3–4 orders of magnitude faster than bulk diffusion with a higher activation energy. For the interface of the composite cathode, the LSCF–LSCrF diffusion couple displayed lower bulk diffusion barrier of ~1.5 eV, accompanied by accelerated grain boundary transport.
In this doctoral research, a model MIEC perovskite oxide, (La0.8Sr0.2)0.95Cr0.5Fe0.5O3-d (LSCrF8255) has been investigated. Secondary ion mass spectrometry (SIMS) was performed to examine the high-temperature surface behavior under various thermal histories. In addition, a series of diffusion couples were fabricated, covering cathode-electrolyte and composite cathode. Characterization provided insight into cation diffusion and interfacial evolution.
Regarding high-temperature surface behavior, it was demonstrated that temperature was the dominant factor governing A-site enrichment, while B-site cation was influenced by surface rearrangement and demixing. Under oxygen-deficient atmosphere, it was observed that at lower temperature led to more severe Sr segregation compared to oxidizing condition. The difference gradually diminished with increasing temperature. Also, Sr segregation exhibited a saturation effect due to limited availability on surface sites. The kinetics of Sr segregation revealed strong dependence on oxygen partial pressure, with the activation energy reduced by approximately 0.6 eV under oxygen-deficient atmosphere.
In terms of interfacial evolution, the GDC–LSCrF and LSGM–LSCrF diffusion couples exhibited strong interdiffusion at elevated temperature. The activation energy of bulk diffusion was approximately 2 eV, while grain boundary diffusion was 3–4 orders of magnitude faster than bulk diffusion with a higher activation energy. For the interface of the composite cathode, the LSCF–LSCrF diffusion couple displayed lower bulk diffusion barrier of ~1.5 eV, accompanied by accelerated grain boundary transport.
Version
Open Access
Date Issued
2025-09-14
Date Awarded
2026-03-01
Copyright Statement
Attribution-Non Commercial-No Derivatives 4.0 International Licence (CC BY-NC-ND)
Advisor
Skinner, Stephen
Marquardt, Katharina
Publisher Department
Department of Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)