Structural transitions in NaBH4 under pressure

The structure of the technologically important hydrogen storage compound NaBH$_{4}$ has been investigated under pressures up to 30 GPa by \textit{in situ} angle dispersive high pressure x-ray diffraction using synchrotron x-rays and a diamond anvil cell. Our experimental results show pressure-induced structural transitions of $\alpha $-NaBH$_{4}$ (cubic -- \textit{Fm3m}) to $\beta $ -- NaBH$_{4}$ (tetragonal -- $P42_{1}c)$ at 6.3 GPa and further to orthorhombic phase (\textit{Pnma}) at 8.9 GPa. The high pressure orthorhombic phase is found to be stable up to 30 GPa. The cubic phase is completely recovered on releasing the pressure to the ambient.