High-pressure transformations and Ionic conductivity in Low-Z Complex hydride LiBH4

Abstract

An X-ray diffraction measurement and a density functional theory (DFT) calculation of the pressure-induced transformation in LiBH4 were performed. The structure of its first high pressure phase at room temperature (phase-III) was determined to be I41/acd structure, whose unit cell was a √2 × √2 ×2 supercell of Ama2 structure proposed previously. Pressure-induced transformation from phase-III took place at 16 GPa and the structure of the second high-pressure phase was analyzed as I4/mmm structure (phase-V′), in which hydrogen atoms were disordered. However, an annealing treatment for phase-V′under high-pressure suggested that it was a metastable phase. With the pressure elevated up to 30 GPa, the tetragonal I4/mmm structure was gradually transformed to a cubic Fm3m structure, which has been reported as a stable phase of phase-V previously. The P- T diagram was examined using high-pressure/high-temperature Raman scattering, and pressure/temperature dependence of the relative ionic conductivity was observed across the phase boundaries. © 2011 The Japan Society of High Pressure Science and Technology.