In this paper, I review my previous research which was designed and conducted for understanding the roles of hydrogen in the evolution of Earth and planets. I first describe the research on hydrogen incorporation reaction into metallic core of the Earth, which occurred while iron and water reacted during the accretion stage of the early Earth. It was conducted as a PhD thesis, and since then my research was dedicated for understanding hydrogen's behaviors at high pressure conditions, as collectively summarized here. The other described research includes high-pressure high-resolution nuclear magnetic resonance spectroscopy using diamond anvil cells, laser-driven shock compression experiments of planetary ice materials, and structural analysis of deep-Earth hydrous minerals using time-of-flight neutron diffraction.
Brief history and the current status of synthesis and applications of nano-polycrystalline diamond (NPD) have been reviewed, as an example of serendipity in basic science, which led to a novel material useful in both scientific and industrial applications. NPD was first witnessed as a tiny piece of glassy transparent material in the wreckage product of an unsuccessful high-pressure experiment, when the author was studying phase transitions of a basaltic composition in a graphite capsule in the mid-1980s. Since then, a number of trial-and-error experiments were made over 15 years, and the author found it was well-sintered polycrystalline material made of nano-crystalline diamond directly converted from graphite under very high pressure and temperature. The NPD was also found to be extremely hard, even harder than natural single crystal diamond. Efforts were made to produce the NPD samples with higher quality and larger sizes, and those with dimensions up to 1 cm in both diameter and length became available by using a large-volume Kawai-type multianvil apparatus (KMA) in the early 2010s. Since then, successful applications of this novel ultra-hard material have been made in high-pressure geoscience, physics, chemistry, and materials science. NPD has also been used for some industrial applications, and known as the very first material successfully commercialized using ultrahigh-pressure synthesis method with the KMA technology. Some novel materials such as Transparent Nano-Ceramics have been synthesized using the similar technique of ultrahigh-pressure synthesis, leading to the development of a new research field “ultra-high pressure materials science”.
Hitachiite (IMA2018-027), ideally Pb5Bi2Te2S6, has been discovered from the Hitachi mine, Ibaraki Prefecture, Japan. Hitachiite commonly occurs as small size of crystals (∼ 30-50 μm) with euhedral hexagonal plate form within pyrite crystals, and co-exists with pyrite, chalcopyrite, sphalerite, pyrrhotite, and galena. Hitachiite shows a metallic luster and black streak, and its macroscopic color is silver grey. Hitachiite has a Mohs' hardness of 2½-3, and its calculated density is 7.54 g/cm3. The discovered hitachiite has trigonal symmetry with a = 4.2200(13) Å, c = 27.02(4) Å. Its space group is P3m1. Hitachiite has a layer-type structure based on ABC-type closed packing of each single element atomic sheet stacked along the c-axis. The stacking sequence is -Te-Bi-S-Pb-S-Pb-S-Pb-S-Pb-S-Pb-S-Bi-Te- (15 layers). It is possible that hitachiite would be forming a homologous series expressed as Bi2Te2S・nPbS with tetradymite (n = 0), aleksite (n = 1), and suddlebackite (n = 2).