Raman Spectroscopy Measurements of the Pressure−Temperature Behavior of LiAlH₄

Abstract

The pressure/temperature phase diagram of LiAlH 4 has been constructed by using Raman spectroscopy data. In situ high pressure-temperature experiments were carried out using resistively heated diamond anvil cells up to 150 °C and 7 GPa. Room temperature phase transitions of monoclinic R-LiAlH 4 f δ-LiAlH 4 were observed at ∼3.2 GPa. As the temperature is increased to ∼100 °C, both the R and δ phases transform to β-LiAlH 4 and remain stable up to 5.5 GPa. At temperatures greater than 300 °C, a new γ-LiAlH 4 phase forms. Data of Konovalov (1995) has been used to define the phase boundary between βand γ-LiAlH 4 phases. We present a pressure-temperature phase diagram of LiAlH 4 based using diamond anvil cells coupled with Raman spectroscopy.

Hydrogen release from Li alanates originates in molecular lattice instability emerging at ∼100 K

“…For example, a Raman spectroscopy study of LiAlH 4 showed alpha, beta, gamma, and delta-phases and their coexisting phases in the pressure-temperature phase diagram of 0-7.5 GPa and 0-600 C. This suggests the existence of many meta-stable atomic positions. 22 Further, neutron diffraction studies of LiAlD 4 at 8 K reported that the DebyeWaller factor (displacement factors) for D is much larger than those for Li and Al, which are anisotropic. 4,23 This also suggests that the stable atomic positions are quite complex and uncertain.…”

Enhanced hydrogen storage properties of LiAlH4 catalyzed by CoFe2O4 nanoparticles

“…Among numerous possible hydrogen storage materials, lithium aluminum hydride [7][8][9][10] (LiAlH 4 ) is a promising candidate due to its relatively large theoretical hydrogen storage capacity and high potential reversible hydrogenation capability.…”

Mobility and dynamics in the complex hydrides LiAlH4 and LiBH4

“…Again, the vibrations split due to the distortion of the AlH À 4 units and crystal field (see symmetry analysis published in the supporting information of ref. 36). Bureau et al, 37 Hagemann et al 36 and Chellappa et al 38 have extensively studied and assigned the corresponding Raman transitions.…”

“…36). Bureau et al, 37 Hagemann et al 36 and Chellappa et al 38 have extensively studied and assigned the corresponding Raman transitions.…”