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Abstract
A high-pressure Raman study was carried out on NaAlH4 up to 17 GPa using the diamond anvil cell method. In the pressure region 2–5 GPa, several of the original modes split. Although this might be a sign of some structural change, the spectral changes do not allow us to claim the existence of a clear phase transition in this pressure range. The spectra revert to their ambient pressure forms on decreasing pressure below<3.0–1.4 GPa. A phase transition to β-NaAlH4 was found at 14–16 GPa. This phase transition is also reversible with an unusually strong hysteresis: the β-NaAlH4 can be followed upon decompression down to 3.9 GPa. Analysis of Raman data shows that this phase transition is compatible with a theoretical prediction of a strong volume collapse.
