I have developed Mito-system —a temperature-pressure variable system for neutron scattering experiments, which contributes recent studies on ice polymorphs. Here I review the current understanding for ice polymorphs including my recent studies, particularly on the following topics: (1) Static and dynamic crystal structure of ice Ih, (2) preparation of ice Ic without stacking disorder, (3) stability and crystal structure of ice XI, (4) symmetry, crystal structure and (potential) order-disorder transition in ice II and III, (5) relation between ice IV and high density amorphous ice, and (6) discovery of ice XVIII at extreme pressure-temperature conditions. Remained open questions for respective polymorphs are also discussed.
Fluid inclusions in high-pressure type metamorphic rocks provide direct information of the deep fluid activity. However, their small size occasionally prevent detailed geochemical study of fluid inclusions. To overcome this difficulty, we applied crush-leach method to quartz veins developed during or near the peak metamorphic stage. Another possible solution is a focused ion beam that allows us precise machining of the solid material. The fluid inclusion study combined with conventional petrographic studies revealed the nature of fluid (and related material) cycle in the subduction zone.
Another powerful approach to investigate the material transfer is so-called “data-driven approach” that employs high-dimension dataset and machine-learning techniques. NMF analysis applied to the Sanbagawa metapelite dataset revealed an evolutional change of the whole-rock composition with metamorphic grade.
Calcium carbonate is the main inorganic component of nonvertebrate hard tissues such as coral and shells. It has also attracted attention for its applications in biomaterials and cancer therapy because of its excellent biocompatibility. Various polymorphs of calcium carbonate exhibit different physicochemical properties which greatly affect their metabolisms in vivo. Therefore, a method for controlling the polymorphism of calcium carbonate could benefit the field of biomineralization and biomaterials in general. In this study, the difference between nonvertebrate calcium carbonate and vertebrate calcium phosphate and the roles of PO4 in calcium carbonate formation were investigated. Three roles of PO4 in the formation of calcium carbonate were identified: an amorphous phase stabilization, a pinning effect of the crystalline phases and inducing that phases are sensitive to PO4. The results of the study indicated that as the concentration of PO4 in the system increased, the calcium carbonate phases were more likely to form thermodynamically unstable phases.