Understanding pressure-driven structural changes in FePO4-II

The room temperature high pressure behaviour of FePO4-I has been investigated and a phase transition at around 2.5 GPa to the orthorhombic phase (FePO4-II) accompanied by a significant amount of amorphisation is observed but remains a mixture of phase II and amorphous FePO4. Such behaviour is similar to that seen in SiO2, and it is this reason why this material is studied at high pressure as it is an analogue for geologically relevant materials. The presence of the amorphous material means that studying the behaviour of FePO4-II at high pressure is hindered. It is the aim of this study to study the high pressure behaviour of FePO4-II without the presence of the amorphous contaminant. Also utilising the unique properties of neutrons it will be possible to determine accurate oxygen positions and hence the tilting mechanisms of the two type of polyhedra.