Ab initio P-T phase diagram of NaBH4

Abstract

We have studied structural stability of cubic (Fm (3) over barm) and tetragonal (P (4) over bar2(1)c) phases of NaBH4 in the P-T plane. Electronic density of states and dielectric constants (epsilon(infinity)), 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. (c) 2006 Elsevier Ltd. All rights reserved.