Structural Phase Transitions in the Potential Hydrogen Storage Compound KBH4 under Compression

Angle-dispersive high-pressure powder X-ray diffraction, high-pressure Raman, and ab initio density functional theoretical (DFT) calculations were performed on KBH4 up to 20 GPa. We demonstrate that KBH4 exhibits structural phase transitions from the ambient α-KBH4 phase (cubic Fm3m) to β-KBH4 (tetragonal P421c) at 3.8 GPa and to the γ-KBH4 phase (orthorhombic Pnma) at 6.8 GPa, which is similar to the phase transition sequence observed for NaBH4 earlier. The transition pressure and bulk modulus obtained for KBH4 in our experiments are in good agreement with theoretical calculations. The results further show that the ambient pressure phase of this hydride is reversible.