Crystal Morphology and Phase Transformation of LiAlO₂: Combined Experimental and First-Principles Studies

Journal Article · Mon Dec 03 04:00:00 EST 2018 · Journal of Physical Chemistry. C

DOI:https://doi.org/10.1021/acs.jpcc.8b09716· OSTI ID:1484282

Heo, Su Jeong ^[1]; Batra, Rohit ^[2]; Ramprasad, Rampi ^[2]; Singh, Prabhakar ^[3]

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1. Univ. of Connecticut, Storrs, CT (United States); University of Connecticut
2. Georgia Inst. of Technology, Atlanta, GA (United States)
3. Univ. of Connecticut, Storrs, CT (United States)

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.

• Research Organization: Univ. of Connecticut, Storrs, CT (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE)
• Contributing Organization: FuelCell Energy, Inc., Center for Clean Energy Engineering at the University of Connecticut
• Grant/Contract Number: EE0006606
• OSTI ID: 1484282
• Journal Information: Journal of Physical Chemistry. C, Journal Name: Journal of Physical Chemistry. C Journal Issue: 50 Vol. 122; ISSN 1932-7447
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
LiAlO2
crystal growth
density functional theory
layered metal oxide
surface energy
transmission electron microscopy