Synthesis of novel hydrogen-storage materials, low-Z ternary hydrides, using supercritical fluid hydrogen

This study has been accomplished for ternary light-element(low-Z)hydrides，which have been paid attention to as new hydrogen-storage materials recently.We have explored synthesis of a new high-density low-Z hydride under high-pressure(HP)and high-temperature(HT)conditions and observation of the reaction process using an outer-heated diamond-anvil-cell.Especially，we aimed at the synthesis a novel low-Z hydride like LiBeH_3，which is quite difficult to be produced，using with supercritical fluid of hydrogen.As regarding the synthesis of LiBeH_3，HP Raman scattering suggested a synthesis of a new hydride in a reaction product between LiH and Be，which has been treated in hydrogen of 7 GPa and 300·C.However，no diffraction peak was between LiH and Be，Higher pressure/temperature conditions may promote the reaction of LiH+Be and to make the product improved in crystallinity.As related studies，HP behaviors of amorphous BeH_2，LiBH_4，LiALH_4，and NaAlH_4have been examined using HP XRD，Raman scattering，infrared absorption and Brillouin scattering measurements.As regards amorphous BeH_2，the polymerization of BeH_2molecules was suggested at about50 GPa。LiBH_4was transformed to some HP phases at1，16 and 30 GPa and the structures of the HP phases were analyzed by means of HP XRD.The structure above 30 GPa was the same with the structure of NaBH_4at ambient pressure，which revealed the structural sequence of alkali-metal borohydrides under HP.In the case of the two alanates，LiALH_4 and NaAlH_4，some HP transformations were observed but it was difficult to analyze the structures because they showed broad XRD patterns.However，it is worthy to note that a new HP/HT phase of NaAlH_4was produced under the conditions of 13 GPa and 280·C.It suggests that HP/HT conditions even below300·C have the potential to produce various kinds of novel interesting phases in the low-Z hydrides already know.

This study has been accomplished for ternary light-element (low-Z) hydrides, which have been paid attention to as new hydrogen-storage materials recently. We have explored synthesis of a new high-density low-Z hydride under high-pressure (HP) and high-temperature (HT) conditions and observation of the reaction process using an outer-heated diamond-anvil- cell. Especially, we aimed at the synthesis a novel low-Z hydride like LiBeH_3, which is quite difficult to be produced, using with supercritical fluid of hydrogen.As regarding the synthesis of LiBeH_3, HP Raman scattering suggested a synthesis of a new hydride in a reaction product between LiH and Be, which has been treated in hydrogen of 7 GPa and 300・C. However, no diffraction peak was observed from the product using HP x-ray diffraction (XRD). Higher pressure/temperature conditions may promote the reaction of LiH + Be and to make the product improved in crystallinity.As related studies, HP behaviors of amorphous BeH_2, LiBH_4, LiALH_4, and NaAlH_4 have been examined using HP XRD, Raman scattering, infrared absorption and Brillouin scattering measurements. As regards amorphous BeH_2, the polymerization of BeH_2 molecules was suggested at about 50 GPa. LiBH_4 was transformed to some HP phases at 1, 16 and 30 GPa and the structures of the HP phases were analyzed by means of HP XRD. The structure above 30GPa was the same with the structure of NaBH_4 at ambient pressure, which revealed the structural sequence of alkali-metal borohydrides under HP. In the case of the two alanates, LiALH_4 and NaAlH_4, some HP transformations were observed but it was difficult to analyze the structures because they showed broad XRD patterns. However, it is worthy to note that a new HP/HT phase of NaAlH_4 was produced under the conditions of 13 GPa and 280・C. It suggests that HP/HT conditions even below 300・C have the potential to produce various kinds of novel interesting phases in the low-Z hydrides already known.