Polymorphism and Thermodynamics of Y(BH4)3 from First Principles
- Polymorphism and Thermodynamics of Y(BH4)3 from First Principles
- 이영수; 심재혁; 조영환
- hydrogen storage
- Issue Date
- The journal of physical chemistry. C, Nanomaterials and Interfaces.
- VOL 114, NO 29, 12833-12837
- 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.
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