Spectroscopic and structural investigations of α‐, β‐, and γ‐AlH3 phases

With its reputation as a high-energy density fuel, aluminum hydride (AlH3) has received renewed attention as a material that is particularly suitable, not only for hydrogen storage but also for rocket propulsion. While the various phases of AlH3 have been investigated theoretically, there is a shortage of experimental studies corroborating the theoretical findings. In response to this, we present here an investigation of these compounds based primarily on two research areas in which there is the greatest scarcity of information in the literature, namely Raman and infrared (IR) absorption analysis. To the authors' knowledge, this is the first report of experimental far-IR absorption results on these compounds. Two different samples prepared by broadly similar ethereal reactions of AlCl3 with LiAlH4 were analyzed. Both Raman and IR absorption measurements indicate that one sample is purely γ-AlH3 and that the other is a mixture of α-, β-, and γ-AlH3 phases. X-ray diffraction confirms the spectroscopic findings, most notably for the β-AlH3 phase, for which optical spectroscopic data are reported here for the first time. Copyright © 2010 John Wiley & Sons, Ltd.