Polymorphism and Thermodynamics of Y(BH4)3 from First Principles

Title
Polymorphism and Thermodynamics of Y(BH4)3 from First Principles
Authors
이영수심재혁조영환
Keywords
hydrogen storage
Issue Date
2010-07
Publisher
The journal of physical chemistry. C, Nanomaterials and Interfaces.
Citation
VOL 114, NO 29, 12833-12837
Abstract
Structure and thermodynamics of the recently discovered two polymorphs of Y(BH4)3 are investigated by first-principles calculation. Simulated X-ray and neutron diffraction patterns combined with structure analysis from first principles enable us to assign a space group Fm3c to the high-temperature polymorph among the several proposed space groups. An orientational disorder of [BH4]- groups is considered and compared with NaBH4, which has a disordered [BH4]- arrangement at room temperature. In the case of NaBH4, the structure stays in a local energy minimum irrespective of the [BH4]- orientation, but in Y(BH4)3, [BH4]- reorientation is suppressed by a strong repulsive force created by close H-H contacts and the structure becomes unstable, thus favoring an ordered [BH4]- arrangement. The calculated high energy barrier for the [BH4]- reorientation partly accounts for the slow phase transition observed in Y(BH4)3, again making a good contrast with the facile [BH4]- flipping in NaBH4. The thermodynamics of Y(BH4)3 appears quite attractive, exhibiting a lower dissociation temperature than Mg(BH4)2 under 1 bar of H2.
URI
http://pubs.kist.re.kr/handle/201004/37725
ISSN
1932-7447
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KIST Publication > Article
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