Abstract

Ammonia borane (BH3NH3) is a promising hydrogen storage material because of its high gravimetric (19.6 wt.% H2) and volumetric hydrogen density with an accompanying moderate decomposition temperature. Previously reported structures determined by using x-ray and neutron diffraction on hydrides show differences in bond lengths and atomic coordination. Here, the crystal structures of fully and half deuterated ammonia borane were investigated as a function of temperature using powder neutron diffraction. the neutron diffraction patterns show a significant difference due to large difference in the scattering length of D and H. It is evident that an order-disorder phase transition occurs around 225 K for all compounds. at low temperature, the compound crystallizes in the orthorhombic structure with space group Pnm21 and gradually transforms to a high temperature disordered tetragonal structure with space group I/4mm at about 225K. the differential scanning calorimetry studies confirm this phase transformation and also indicate that all compounds melt and decompose at above 370 K. the c cell parameter remains unchanged in the orthorhombic phase from 16 K to 200K and increases lia nearly above 225K. as the temperature is increased, the BH 3-NH3 groups start to reorient along the c axis, and the D/H atoms become disordered, leading to the tetragonal phase transition around 225K.

Department(s)

Chemistry

Second Department

Physics

Keywords and Phrases

Crystal structure; Hydrogen storage; Neutron diffraction; Phase transition

International Standard Book Number (ISBN)

978-087849340-1;978-087849340-1;978-087849340-1

International Standard Serial Number (ISSN)

1662-9752; 0255-5476

Document Type

Article - Conference proceedings

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2024 Trans Tech Publications, All rights reserved.

Publication Date

01 Jan 2009

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