New Structures Of AlH₃ At High Pressure Predicted By A First-principles Study

Since the situation of global warming and the fossil fuel depletion become more and more serious, the development of hydrogen energy, as the next generation of secondary clean energy, is an urgent need. However, in the realization of hydrogen energy utilization, the hydrogen storage and transportation are the main issues which are needed to be solved at present.At all times, different and new programs of the hydrogen storage appear successively. Recently, as a technology of solid hydrogen storage, the new hydrogen storage alloy is developing quickly. Now, AIH3 as a hydrogen storage material has got actively developed. This material is an hydride which has a higher hydrogen content. Its density of hydrogen storage is 10.1wt.% (Quality percentage) much higher than previous hydrogen storage alloy 2～3 wt.% quality storage density. What's more, its hydrogen storage density also reached 149g/L (which is more than double the density of liquid hydrogen).Therefore, the material has aroused great interest. In recent years, a lot of researches about AIH3 have been done at room temperature. The present results show that:this material has existed at least 10 different phase at room temperature. At the same time, from the early seventies, people began to explore the possibility of using the solid state hydride as a beginning way to get the metallic hydrogen, and whether the conditions can be obtained the high capacity of hydrogen and the stable solid hydride fuel under high pressure. Then people began to study the nature of the AlH3 under high pressure.Currently, through the theoretical and experimental results, it shows that in the process of increasing pressure;AlH3 phase transition will occur as the following process:the most stable phase under the atmospheric pressure a phase→Pnma→P m-3n and their corresponding transition pressures were 34GPa and 73GPa. In this article, we apply the first-principle to continue to study that AlH3 possible happen the phase transition and exist of a more stable structure under a higher pressure (>73GPa). By the stable phase R-3C, Pnma, Pm-3n and Pbcm at atmospheric pressure, we have done the molecular dynamics simulation and the optimization, so getting some new stable phase. Then we get the graph which can manifest the total energy of these structures change with the different sizes of the structures by calculating. The analysis shows that there is a structure P1 but without symmetry and the transitional pressure is 370GPa when Pm-3n phase turns into P1 phase.