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Title: Density functional theory + U analysis of the electronic structure and defect chemistry of LSCF (La 0.5 Sr 0.5 Co 0.25 Fe 0.75 O 3-δ )

Abstract

Reducing operating temperatures is a key step in making solid oxide fuel cell (SOFC) technology viable. A promising strategy for accomplishing this goal is employing mixed ion–electron conducting (MIEC) cathodes. La 1-xSr xCo 1-yFe yO 3-δ (LSCF) is the most widely employed MIEC cathode material; however, rational optimization of the composition of LSCF requires fundamental insight linking its electronic structure to its defect chemistry. To provide the necessary insight, density functional theory plus U (DFT+U) calculations are used to investigate the electronic structure of LSCF (xSr = 0.50, yCo = 0.25). The DFT+U calculations show that LSCF has a significantly different electronic structure than La 1-xSr xFeO 3 because of the addition of cobalt, but that minimal electronic structure differences exist between La 0.5Sr 0.5Co 0.25Fe 0.75O 3 and La 0.5Sr 0.5Co 0.5Fe 0.5O 3. The oxygen vacancy (V$$-\atop{o}$$) formation energy (ΔEf,vac) is calculated for V$$-\atop{o}$$ residing in different local environments within La 0.5Sr 0.5Co 0.25Fe 0.75O 3. These results show that Co-V$$-\atop{o}$$-Co configurations have the highest ΔEf,vac, while Co-V$$-\atop{o}$$-Fe have the lowest ΔEf,vac and may act as traps for V$$-\atop{o}$$. We conclude that compositions with more Fe than Co are preferred because the additional Co-V$$-\atop{o}$$-Co sites would lead to higher overall ΔEf,vac (and lower V$$-\atop{o}$$ concentrations), while the trapping strength of the Image Co-V$$-\atop{o}$$-Fe sites is relatively weak (~0.3 eV).

Authors:
; ;
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Heterogeneous Functional Materials Center (HeteroFoaM)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1370135
DOE Contract Number:  
SC0001061
Resource Type:
Journal Article
Journal Name:
Physical Chemistry Chemical Physics. PCCP (Print)
Additional Journal Information:
Journal Volume: 18; Journal Issue: 17; Related Information: HeteroFoaM partners with University of South Carolina (lead); University of California, Santa Barbara; University of Connecticut; Georgia Institute of Technology; Princeton University; Rochester Institute of Technology; Savannah River National Laboratory; University of South Carolina; University of Utah; Journal ID: ISSN 1463-9076
Publisher:
Royal Society of Chemistry
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Ritzmann, Andrew M., Dieterich, Johannes M., and Carter, Emily A. Density functional theory + U analysis of the electronic structure and defect chemistry of LSCF (La 0.5 Sr 0.5 Co 0.25 Fe 0.75 O 3-δ ). United States: N. p., 2016. Web. doi:10.1039/c6cp01720g.
Ritzmann, Andrew M., Dieterich, Johannes M., & Carter, Emily A. Density functional theory + U analysis of the electronic structure and defect chemistry of LSCF (La 0.5 Sr 0.5 Co 0.25 Fe 0.75 O 3-δ ). United States. doi:10.1039/c6cp01720g.
Ritzmann, Andrew M., Dieterich, Johannes M., and Carter, Emily A. Fri . "Density functional theory + U analysis of the electronic structure and defect chemistry of LSCF (La 0.5 Sr 0.5 Co 0.25 Fe 0.75 O 3-δ )". United States. doi:10.1039/c6cp01720g.
@article{osti_1370135,
title = {Density functional theory + U analysis of the electronic structure and defect chemistry of LSCF (La 0.5 Sr 0.5 Co 0.25 Fe 0.75 O 3-δ )},
author = {Ritzmann, Andrew M. and Dieterich, Johannes M. and Carter, Emily A.},
abstractNote = {Reducing operating temperatures is a key step in making solid oxide fuel cell (SOFC) technology viable. A promising strategy for accomplishing this goal is employing mixed ion–electron conducting (MIEC) cathodes. La1-xSrxCo1-yFeyO3-δ (LSCF) is the most widely employed MIEC cathode material; however, rational optimization of the composition of LSCF requires fundamental insight linking its electronic structure to its defect chemistry. To provide the necessary insight, density functional theory plus U (DFT+U) calculations are used to investigate the electronic structure of LSCF (xSr = 0.50, yCo = 0.25). The DFT+U calculations show that LSCF has a significantly different electronic structure than La1-xSrxFeO3 because of the addition of cobalt, but that minimal electronic structure differences exist between La0.5Sr0.5Co0.25Fe0.75O3 and La0.5Sr0.5Co0.5Fe0.5O3. The oxygen vacancy (V$-\atop{o}$) formation energy (ΔEf,vac) is calculated for V$-\atop{o}$ residing in different local environments within La0.5Sr0.5Co0.25Fe0.75O3. These results show that Co-V$-\atop{o}$-Co configurations have the highest ΔEf,vac, while Co-V$-\atop{o}$-Fe have the lowest ΔEf,vac and may act as traps for V$-\atop{o}$. We conclude that compositions with more Fe than Co are preferred because the additional Co-V$-\atop{o}$-Co sites would lead to higher overall ΔEf,vac (and lower V$-\atop{o}$ concentrations), while the trapping strength of the Image Co-V$-\atop{o}$-Fe sites is relatively weak (~0.3 eV).},
doi = {10.1039/c6cp01720g},
journal = {Physical Chemistry Chemical Physics. PCCP (Print)},
issn = {1463-9076},
number = 17,
volume = 18,
place = {United States},
year = {2016},
month = {1}
}

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