Structural Study on Ammonia Borane for Hydrogen Storage
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 BH3-NH3 groups start to reorient along the c axis, and the D/H atoms become disordered, leading to the tetragonal phase transition around 225K.
Hydrogen Storage Crystal Structure Neutron Diffraction Phase Transition
W.J. JAMES L. JAGAT Q. CAI W.B. YELON J.B. YANG
Materials Research Center and Department of Chemistry,Missouri University of Science & Technology, R Department of Physics, University of Missouri, Columbia, MO 65211, USA Materials Research Center and Department of Physics,Missouri University of Science & Technology, Rol
国际会议
重庆
英文
425-430
2008-06-09（万方平台首次上网日期，不代表论文的发表时间）