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Examination of pressure,temperature (P,T)-conditions necessary for aluminium hydride preparation reveals that high pressure favors the formation of thermodynamically unstable AlH3. Both elemental reactions and solid-state Schlesinger exchange reactions facilitate the preparation of AlH3 at high pressures. Experimental data suggests alpha-AlH3 as the most stable phase. Formation of AlH3 from AlCl3 and LiH occurs only at temperatures and pressures higher than 5.6 GPa and 550 degrees Celsius, respectively.

Aluminum trihydride (alane) crystallizing in the [gamma]-Al[H.sub.3] polymorphic modification was combined and structurally characterized by synchrotron X-ray powder diffraction. The crystal structure of [gamma]-Al[H.sub.3] is composed of Al[H.sub.6] octahedra as the building blocks and it forms a bifurcated double-bridge bond Al-2H-Al.

Single-phase ternary deuteride Li2BeD4 was synthesized by a high-pressure high-temperature technique from LiD and BeD2. The crystal structure of Li2BeD4 was solved from X-ray and neutron powder diffraction data. The compound crystallizes in the monoclinic space group P21/c with lattice parameters a = 7.06228(9) Å, b = 8.3378(1) Å, c = 8.3465(1) Å, β =93.577(1)°, and Z = 8. Its structure contains isolated BeD4 tetrahedra and Li atoms that are located in the structure interstices. Li2BeD4 does not undergo any structural phase transitions at temperatures down to 8 K. [ABSTRACT FROM AUTHOR]

Powder samples of cristobalite-I are loaded with hydrogen at pressures up to 90 kbar and T = 250 °C and quenched under pressure to the liquid N2 temperature. The quenched samples are examined at ambient pressure by X-ray diffraction, Raman spectroscopy, and thermal desorption analysis. The hydrogen content of the samples is found to increase with pressure and reach a molecular ratio of H2/SiO2 ∼ 0.10 at P = 90 kbar. At ambient pressure, the samples consist of a mixture of approximately 80% cristobalite-I phase and 20% cristobalite-II-like phase, the crystal lattices of both phases being slightly expanded due to the hydrogen uptake. According to Raman spectroscopy, the hydrogen is dissolved in these phases in the form of H2 molecules.

The solubility of hydrogen in amorphous silica at a temperature of 250 °C and pressures up to 75 kbar is studied using a quenching technique. The molar ratio H(2)/SiO(2) is found to linearly increase with pressure from X = 0.16 at P = 6 kbar to X = 0.53 at P = 75 kbar. An investigation of a sample with X = 0.47 by Raman spectroscopy demonstrated that hydrogen dissolves in silica in the form of H(2) molecules, and these molecules occupy voids of, at least, two different types in the silica network. An X-ray diffraction study showed that the hydrogen molecules penetrating in the silica glass network prevented its irreversible densification occurring if the silica glass is compressed to the same pressure without hydrogen.

Single-phase ternary deuteride Li(2)BeD(4) was synthesized by a high-pressure high-temperature technique from LiD and BeD(2). The crystal structure of Li(2)BeD(4) was solved from X-ray and neutron powder diffraction data. The compound crystallizes in the monoclinic space group P2(1)/c with lattice parameters a = 7.06228(9) A, b = 8.3378(1) A, c = 8.3465(1) A, beta =93.577(1) degrees, and Z = 8. Its structure contains isolated BeD(4) tetrahedra and Li atoms that are located in the structure interstices. Li(2)BeD(4) does not undergo any structural phase transitions at temperatures down to 8 K.