Solid, hydrogen-rich compounds, such as alkali metal hydrides, MAH4, where
M is an alkali metal and A is boron or aluminium, may be used for hydrogen
storage. We briefly review recent high-pressure work in this field aimed at
exploring the phase behaviour, and especially the possibility to find highly
dense new structures. In particular we present experimental data on the
structure, lattice dynamics, phase diagrams, and thermal properties obtained by
us and others by Raman scattering, x-ray diffraction, and thermal conductivity
measurements under pressure between 100 and 400 K. From these data and the
results of theoretical calculations we map observed structural phases and phase
transitions in the pressure–temperature plane for the materials that have so far
been investigated under pressure.