軽元素錯体水素化物 LiBH_4の高圧構造相転移とイオン伝導特性

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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 Fm<span style="text-decoration:overline;">3</span>m 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.
2011-08-20