Stability enhancement by particle size reduction in AlH3

Phase stability of nano-structures and possible low energy surfaces of AlH3 polymorphs from thin film geometry have been investigated using all electron density-functional total energy calculations. The calculated structural data for alpha-, alpha'-, beta-, and gamma-AlH3 modifications are in very good agreement with experimental values. The electronic structures based on parameterized HCTH functionals reveal that all polymorphs are insulators with calculated band-gap varying between 2.53 and 4.41 eV. From our theoretical simulation we have found that the (0 1 0) in alpha-, (1 0 0) in alpha'-, (1 0 1) in beta-, and (1 0 1) in gamma-AlH3 surfaces are the most stable surface in the corresponding polymorphs. We have predicted that the critical size for the AlH3 nano-cluster is less than 1 nm. As opposite to complex hydrides we have investigated so far, the calculated formation energy as a function of particle size reveal that the nano particles of AlH3 are relatively stable than the corresponding decomposed phases. (C) 2010 Elsevier B.V. All rights reserved.