Ammonia borane at low temperature down to 90 K and high pressure up to 15 GPa

We have studied the phase transformation behavior of the potential hydrogen storage compound ammonia borane at low temperature (from room temperature down to 90 K) and high pressure (from ambient pressure to 9.5 GPa at room temperature and up to 15 GPa at 90 K) region using the diamond anvil cell. This material shows four new phase transitions in this pressure and temperature region. The phase transition phenomenon is evidenced by the splitting of the peak and/or the appearance of the new peak in the Raman spectra as well as by the change of the pressure coefficient of the Raman modes. The phase boundaries between these phases are also established from the data collected during different cooling cycles. These results provide the information about the stability of the bonding characteristics of this potential hydrogen storage material at low temperature and high pressure region.