Research

The density deficit of 10% in the outer core and 4% in the inner core compared to pure iron suggests that hydrogen was dissolved in iron during the early stages of Earth's evolution. We use a very unique technique, high-pressure neutron diffraction, to investigate crystal structure, phase diagram, and thermodynamic properties of iron hydride(s) at high temperatures and high pressures.

Water is the most ubiquitous substance, but has a lot of unresolved problems.

When compressed over 1 GPa at room temperature, water freezes into an ice phase called ice VI. In fact, there are more than 20 ice polymorphs under varying pressure-temperature conditions. Recently, we have discovered a new phase of ice, ice XIX, through in-situ dielectric & neutron-diffraction experiments under high pressure. Moreover, we have succeeded in the preparation of ice Ic without stacking disorder and in elucidation of ice VII's detailed atomic distributions & proton-dynamics crossover at about 10 GPa.

From viewpoints of planetary science, it is important to investigate salty ice to understand deep interior of icy planets because a high-pressure ice phase (ice VII) can incorporate more than 10 mol% of salts in its crystal structure.

Calcium carbonate (CaCO3) is a typical biomineral that we find in, for example, shells. There are three polymorphs in calcium carbonate: calcite, aragonite, and vaterite and they are all biominerals. Additionally, amorphous calcium carbonate (ACC) works as a precursor of biominerals.

We have focused on the fact that heating and/or compression of ACC result in crystallisation of calcium carbonate polymorphs such as calcite. Since ACC is structurally flexible, calcite crystallised from ACC can incorporate large ions such as Sr2+ and Ba2+. These large ions are usually incompatible to calcite structure. We have discovered that such doped calcite shows anomalous statically disordered nature even at room temperature.

We have performed high-pressure experiments for basic organic chemicals, such as benzene and naphthalene, and revealed that they underwent characteristic oligomerisation or amorphisation reactions. For example, naphthalene irreversibly becomes amorphous at approx. 18 GPa. However, even amorphous naphthalene retained some of the original aromatic features.

We also focus on more bio-related materials: amino acids. Peptization reactions were thought to proceed under high-temperature and/or catalytic conditions, but we have discovered that, in alanine systems, it proceed under high pressures even at room temperature.

We are conducting high-pressure experiments to investigate how such biomolecules would form inside icy satellites and moons.