First-principles study of a hydrogen storage material CaSi

Journal Article · Mon Aug 15 04:00:00 EDT 2005 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PhysRevB.72.075104· OSTI ID:20719324

Ohba, Nobuko; Aoki, Masakazu; Noritake, Tatsuo; Miwa, Kazutoshi; Towata, Shin-ichi ^[1]

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1. Toyota Central Research and Development Laboratories, Inc., Nagakute, Aichi 480-1192 (Japan)

We report the results of the first-principles calculation on the hydrogen storage material CaSi. The stability and bonding nature of CaSi hydride have been investigated theoretically with the ultrasoft pseudopotential method based on the density functional theory before experimentation. Theoretical prediction has suggested that CaSi hydride is thermodynamically stable. In actual measurements [M. Aoki et al., Appl. Phys. Lett. 85 387 (2004)] it is confirmed that CaSi reversibly absorbs and desorbs hydrogen, and the maximum hydrogen content is 1.9 wt % which means CaSi forms CaSiH{sub 1.3}. The hydriding reaction enthalpy of CaSiH{sub 1.3} is estimated as -42 kJ/mol H{sub 2} from the calculation based on the crystal structure symmetry determined by the Rietveld refinements of synchrotron x-ray diffraction data, which is in fairly good agreement with an experimental value of -62 kJ/mol H{sub 2}. From the calculation results of density of states, CaSiH{sub 1.3} has an energy gap of 0.013 eV and the electronic structure is nonmetallic. The charge-density distribution indicates that one Si atom and one H atom are bonding covalently. It is thought that these electronic structures cause the stability of CaSiH{sub 1.3}.

• OSTI ID: 20719324
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Journal Name: Physical Review. B, Condensed Matter and Materials Physics Journal Issue: 7 Vol. 72; ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ATOMS
CALCIUM SILICIDES
CHARGE DENSITY
CHEMICAL BONDS
CRYSTAL STRUCTURE
CRYSTALS
DENSITY FUNCTIONAL METHOD
DISTRIBUTION
ELECTRONIC STRUCTURE
ENERGY GAP
ENERGY LEVELS
ENERGY-LEVEL DENSITY
ENTHALPY
EV RANGE
HYDRIDES
HYDROGEN
HYDROGEN STORAGE
STABILITY
SYMMETRY
X-RAY DIFFRACTION