Low-temperature phase transformation in NaBH4 under pressure

The pressure-temperature structural phase diagram of NaBH4 has been mapped by thermal conductivity measurements below room temperature and up to 2 GPa. The critical transition temperature for the transformation from the low-temperature tetragonal structure to the room temperature cubic one increases from near 190 K at zero pressure to about 235 K at 2 GPa. The thermal conductivity data are consistent with the order-disorder character of the transition.