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Title: Crystal Morphology and Phase Transformation of LiAlO 2: Combined Experimental and First-Principles Studies

Abstract

Layered α-LiAlO 2 matrix often suffers from detrimental structural and morphological changes during its lifetime, especially under H 2 containing fuel inlet environments of molten carbonate fuel cell systems. However, the underlying mechanism of this phase and morphological transformations has rarely been explored. In this study, transmission electron microscopy (TEM) techniques were used to determine the changes in structure and morphology of LiAlO 2 samples lifted by a focused ion beam (FIB). In accordance with X-ray diffraction (XRD) analysis, TEM images show that under H-rich conditions the rhombohedral α-LiAlO 2 transforms to tetragonal γ-LiAlO 2 phase with the appearance of the (101) terminated octahedral shaped γ-LiAlO 2 crystallites. We further support, and plausibly rationalize, the observed transformations using density functional theory (DFT) calculation. The DFT computed surface energies of γ-LiAlO 2 reveal that the {101} surface becomes the lowest energy surface upon H-adsorption, thus leading to formation of observed octahedral geometry. Contrary to stabilization of γ-LiAlO 2 surfaces upon H passivation, DFT revealed H-adsorption on α-LiAlO 2 surfaces to be energetically unfavorable. Furthermore, this contrasting behavior of α-LiAlO 2 and γ-LiAlO 2 under H-rich environments could be a potential driving force for the observed α-LiAlO 2 to γ-LiAlO 2 phasemore » transformation.« less

Authors:
 [1];  [2];  [2];  [1]
  1. Univ. of Connecticut, Storrs, CT (United States)
  2. Georgia Inst. of Technology, Atlanta, GA (United States)
Publication Date:
Research Org.:
Univ. of Connecticut, Storrs, CT (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
Contributing Org.:
FuelCell Energy, Inc., Center for Clean Energy Engineering at the University of Connecticut
OSTI Identifier:
1484282
Grant/Contract Number:  
EE0006606
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Name: Journal of Physical Chemistry. C; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; LiAlO2; crystal growth; surface energy; density functional theory; transmission electron microscopy; layered metal oxide

Citation Formats

Heo, Su Jeong, Batra, Rohit, Ramprasad, Rampi, and Singh, Prabhakar. Crystal Morphology and Phase Transformation of LiAlO2: Combined Experimental and First-Principles Studies. United States: N. p., 2018. Web. doi:10.1021/acs.jpcc.8b09716.
Heo, Su Jeong, Batra, Rohit, Ramprasad, Rampi, & Singh, Prabhakar. Crystal Morphology and Phase Transformation of LiAlO2: Combined Experimental and First-Principles Studies. United States. doi:10.1021/acs.jpcc.8b09716.
Heo, Su Jeong, Batra, Rohit, Ramprasad, Rampi, and Singh, Prabhakar. Wed . "Crystal Morphology and Phase Transformation of LiAlO2: Combined Experimental and First-Principles Studies". United States. doi:10.1021/acs.jpcc.8b09716.
@article{osti_1484282,
title = {Crystal Morphology and Phase Transformation of LiAlO2: Combined Experimental and First-Principles Studies},
author = {Heo, Su Jeong and Batra, Rohit and Ramprasad, Rampi and Singh, Prabhakar},
abstractNote = {Layered α-LiAlO2 matrix often suffers from detrimental structural and morphological changes during its lifetime, especially under H2 containing fuel inlet environments of molten carbonate fuel cell systems. However, the underlying mechanism of this phase and morphological transformations has rarely been explored. In this study, transmission electron microscopy (TEM) techniques were used to determine the changes in structure and morphology of LiAlO2 samples lifted by a focused ion beam (FIB). In accordance with X-ray diffraction (XRD) analysis, TEM images show that under H-rich conditions the rhombohedral α-LiAlO2 transforms to tetragonal γ-LiAlO2 phase with the appearance of the (101) terminated octahedral shaped γ-LiAlO2 crystallites. We further support, and plausibly rationalize, the observed transformations using density functional theory (DFT) calculation. The DFT computed surface energies of γ-LiAlO2 reveal that the {101} surface becomes the lowest energy surface upon H-adsorption, thus leading to formation of observed octahedral geometry. Contrary to stabilization of γ-LiAlO2 surfaces upon H passivation, DFT revealed H-adsorption on α-LiAlO2 surfaces to be energetically unfavorable. Furthermore, this contrasting behavior of α-LiAlO2 and γ-LiAlO2 under H-rich environments could be a potential driving force for the observed α-LiAlO2 to γ-LiAlO2 phase transformation.},
doi = {10.1021/acs.jpcc.8b09716},
journal = {Journal of Physical Chemistry. C},
number = ,
volume = ,
place = {United States},
year = {Wed Nov 28 00:00:00 EST 2018},
month = {Wed Nov 28 00:00:00 EST 2018}
}

Journal Article:
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