Pressure-Temperature Phase Diagram of LiAlH4

Abstract

High pressure behavior of complex hydrides is investigated in this thesis. Raman spectroscopy was performed at different temperatures and pressures to determine structural changes in LiAlH4. In situ high-pressure/high-temperature Raman spectroscopy experiments were carried out using resistively heated diamond anvil cells up to 150°C and 7 GPa. High pressure experiments performed at room temperature showed transformation of the monoclinic alpha-LiAlH4 to delta-LiAlH4 phase at ~3.25 GPa. As the temperature is increased to ~100°C both the alpha and delta phases transform to beta-LiAlH4 and remain stable up to 5.5 GPa. At temperatures greater than 300°C a new gamma-LiAlH4 phase forms. The data obtained in this thesis was used along with that of Konovalov (1995) to construct the PT phase diagram of LiAlH4 and to define beta and gamma-LiAlH4 phase boundaries. Decomposition data of Block and Gray (1965) was also analyzed to define the decomposition boundary.