Structural transition of NaBH 4 under high pressure: Ab initio calculations

Abstract

The pressure induced structural transition of NaBH 4 from β-NaBH 4 (tetragonal- P42 1c ) to γ-NaBH 4 (orthorhombic- Pnma) is investigated by ab initio plane-wave pseudopotential density functional theory method (DFT). The BaSO 4-type structure of orthorhombic high-pressure phase is testified theoretically for the first time. The calculated transition pressure of β-NaBH 4 (tetragonal- P42 1c ) to γ-NaBH 4 (orthorhombic- Pnma) is 9.66 GPa and the orthorhombic high-pressure phase is stable up to 30 GPa. Our results agree well with previous experimental results and demonstrate that high-pressure phase transition from β-NaBH 4 to γ-NaBH 4 may occur at low temperature. At last, the pressure effects on the electronic structures of α-, β- and γ-NaBH 4 are discussed.