Ab initio – phase diagram of NaBH4

We have studied structural stability of cubic ( F m 3 ̄ m ) and tetragonal ( P 4 ̄ 2 1 c ) phases of NaBH4 in the P – T plane. Electronic density of states and dielectric constants ( ϵ ∞ ) , and phonon dispersion curves are also obtained. Well known disordering of [BH4]− tetrahedra in the cubic phase is approximated by 2:2 ordering along [110]. The resulting transition temperature ( T c ) at 0 is 133 K, which is similar to the experimental value ( T c = 190 K ) . The P – T phase diagram is compared with the recently reported experiment for low pressure range, where our result agrees with the experiment qualitatively.