This is a short review of the history of developments in high pressure in situ X-ray diffraction experiments using multi-anvil apparatus, and the role of the late Professor Syun-iti Akimoto in this field. A “DIA-type” apparatus developed in Japan has combined with synchrotron radiation and successfully completed as “MAX-80” apparatus. This technique was transferred to other countries and have made further progress. Prof. Akimoto has played a very important role in these developments.
The first system with DIA type apparatus for synchrotron radiation study named MAX80 was installed at the Photon Factory in 1982. In this article, progress of the kick-off, planning, designing, construction and commissioning of MAX80 is briefly introduced. High pressure X-ray studies have suffered from the weak diffraction intensities, and synchrotron radiation was greatly expected to be a bright X-ray source. This makes the construction of MAX80 as a nation-wide project for high pressure community. Prof. S. Akimoto played an inevitable role, especially in the stage of beginning, in the construction of MAX80.
In this article, the recent standard scenario for formation of the solar system was briefly reviewed, focusing on accretion of the terrestrial planets. The final stage of accreting Earth is characterized by an impact of a Mars-sized planetary embryo, which results in lunar formation. The giant impact, on the other hand, brings extensive melting to the Earth, and a deep magma ocean covers the early Earth. Therefore the primordial state of the evolving Earth is to be decisively controlled through a cooling process of the magma ocean. Chemical fractionation of the mantle in the magma ocean was discussed based on the results of high-pressure melting experiments on mantle materials up to 35 GPa. Importance of melting experiment on Earth’s materials at higher pressure was emphasized in understanding the evolution of the Earth.
Phase equilibria of materials at high pressures and high temperatures are determined by high-pressure and high-temperature experiments, and also by thermodynamic calculation with calorimetric data. The thermodynamic calculation is very useful to examine whether the experimentally determined phase relations are in equilibrium with sufficient accuracy, and to determine the equilibrium phase boundary at pressure-temperaure conditions where equilibrium is difficult to attain in high-pressure experiments. The issues are illustrated in coesite-stishovite transition and rutile-αPbO2 transition in TiO2. Calculated boundaries of postspinel transition in Mg2SiO4 are shown to compare with experimentally determined boundaries along with evaluating effect of cation-disorder in spinel on the boundary slope.
Presence of molecules in a crystal structure produces structural and electronic anisotropy. Such anisotropy can be a cause to yield various novel high-pressure phenomena in molecular crystals. They include pressure-induced metallization, amorphization and recrystallization, molecular formation/dissociation, superconductivity and amorphous-amorphous transition. This report reviews high-pressure behavior of molecular crystal SnI4 which does show those phenomena.
Crystals with both dielectric and magnetic ordering simultaneously have attracted much interest of the researchers for a long time. In such crystals, we can expect various phenomena coming from strong interplay between the two different orders, such as suppression of dielectric constant and electric polarization reversal by magnetic field, etc.. Recent developments in this field are reviewed in this article, which is particularly concentrated on BiMnO3 and related perovskites, and rare earth manganites RMn2O5.
Efforts to synthesize and characterize metal-hydrogen alloys over wide ranges of composition, temperature and hydrogen pressure are described, taking examples mostly from our own experiments. General trends in the phase diagram of M-H systems include (a) drastic melting-point reduction, (b) transition to close-packed structures (hcp, dhcp and fcc) with dissolution of hydrogen, and (c) appearance of an eutectic liquid phase at high H concentrations. Thus, possibilities of synthesizing H-rich alloys at high hydrogen pressures are envisaged. A brief recollection of collaborative work with Professor Akimoto on the Fe-H2O reaction and its implication for the Earth’s core formation is also made.
This article reviews the density and viscosity of magma and metallic liquid at high pressure and high temperature. Because magma and metallic liquid have played important roles in the Earth’s history, we have investigated the physical properties of such liquids at high pressures and high temperatures. Density measurement of liquid is now mainly carried out by the sink/float method and the X-ray absorption method. Falling sphere method is applied to measure the viscosity. The newly established radiography system at SPring-8 enables us to measure the viscosity in situ up to 13.1 GPa and 2470 K.
We investigate pressure-induced structural changes in liquids of tetrahedrally bonded materials by synchrotron x-ray diffraction. The liquids show various structural changes, depending on their ionic characters in the chemical bonds. The liquids with a small ionic character, such as GaSb, InSb, and InAs, show continuous structural changes over a wide pressure region of about 20 GPa. In contrast, those with a large ionic character, such as CdTe and AgI, show drastic structural changes within a narrow pressure region of about 2 GPa. We discuss the effect of the ionicity on the pressure-induced structural changes in the liquids and compare the effect with that in the crystalline phases.