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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]