Structural transition of NaBH4 under high pressure: Ab initio calculations

The pressure induced structural transition of NaBH4 from β-NaBH4 (tetragonal-P421c) to γ-NaBH4 (orthorhombic-Pnma) is investigated by ab initio plane-wave pseudopotential density functional theory method (DFT). The BaSO4-type structure of orthorhombic high-pressure phase is testified theoretically for the first time. The calculated transition pressure of β-NaBH4 (tetragonal-P421c) to γ-NaBH4 (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-NaBH4 to γ-NaBH4 may occur at low temperature. At last, the pressure effects on the electronic structures of α-, β- and γ-NaBH4 are discussed.