title: First-principles calculated decomposition pathways for LiBH4 nanoclusters.
abstract: We analyze thermodynamic stability and decomposition pathways of LiBH4 nanoclusters using grand-canonical free-energy minimization based on total energies and vibrational frequencies obtained from density-functional theory (DFT) calculations. We consider (LiBH4)n nanoclusters with n = 2 to 12 as reactants, while the possible products include (Li)n, (B)n, (LiB)n, (LiH)n, and Li2BnHn; off-stoichiometric LinBnHm (m ≤ 4n) clusters were considered for n = 2, 3, and 6. Cluster ground-state configurations have been predicted using prototype electrostatic ground-state (PEGS) and genetic algorithm (GA) based structural optimizations. Free-energy calculations show hydrogen release pathways markedly differ from those in bulk LiBH4. While experiments have found that the bulk material decomposes into LiH and B, with Li2B12H12 as a kinetically inhibited intermediate phase, (LiBH4)n nanoclusters with n ≤ 12 are predicted to decompose into mixed LinBn clusters via a series of intermediate clusters of LinBnHm (m ≤ 4n). The calculated pressure-composition isotherms and temperature-pressure isobars exhibit sloping plateaus due to finite size effects on reaction thermodynamics. Generally, decomposition temperatures of free-standing clusters are found to increase with decreasing cluster size due to thermodynamic destabilization of reaction products.
authors.affiliation: Department of Physics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan.
authors.forename: Zhi-Quan
authors.initials: ZQ
authors.lastname: Huang
authors.affiliation: Department of Physics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan.
authors.forename: Wei-Chih
authors.initials: WC
authors.lastname: Chen
authors.affiliation: Department of Physics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan.
authors.forename: Feng-Chuan
authors.initials: FC
authors.lastname: Chuang
authors.affiliation: Center for Nanoscience and Department of Physics and Astronomy,University of Missouri-St. Louis, St. Louis, Missouri 63121, United States.
authors.forename: Eric H
authors.initials: EH
authors.lastname: Majzoub
authors.affiliation: Department of Materials Science and Engineering, University of California Los Angeles, Los Angeles, California 90095-1595, USA.
authors.forename: Vidvuds
authors.initials: V
authors.lastname: Ozoliņš