Disordered Structure in Ice VII Observed by Neutron Technique

Ice VII is one of numerous ice polymorphs and is stable at room temperature between 2 and 60 GPa. Its structure can be described using a simple cubic model, so-called a single-site model, sufficient to reproduce its diffraction behaviours for most purposes. At the same time, its disordered nature of molecular orientations associated with slight displacements has been of interest. This article reviews historical challenges to elucidate its disordered structure beyond the simple model and recent achievements from in-situ neutron diffraction under high pressure with “model-free” analyses.