Masaaki Yamakata

High-pressure science with a multi-anvil apparatus at SPring-8

Since first opening its doors to public research in 1997, SPring-8 has seen the accomplishment of many important studies in a wide variety of fields through its stable operation and cutting edge technology. High-pressure experiments have been carried out on a number of beamlines using a diamond anvil cell or a multi-anvil press. Here, we review the multi-anvil presses installed on the SPring-8 beamlines and a few research projects currently utilizing this technology. The significant difference in post-spinel boundary between multi-anvil experiments and diamond anvil studies will also be discussed.

An apparatus to load gaseous materials to the diamond‐anvil cell

An apparatus to load gases to the sample chamber of the diamond‐anvil cell has been devised. The apparatus is driven by a conventional 50 ton hydraulic press and no gas compressor is required. The gas from a commercial gas bomb is compressed to 150 MPa and loaded into the diamond‐anvil cell sample chamber. After loading, the pressure of the diamond‐anvil cell is increased further using the lever and spring mechanism. This kind of gas loading apparatus will become indispensable not only for studying gaseous materials themselves, but also for making precision measurements at high pressures and high temperatures under hydrostatic conditions.

Performance of different types of detectors in a high-pressure X-ray study of phase transition

Abstract Phase transitions in praseodymium and lanthanum under pressure have been studied using a synchrotron powder X-ray diffraction technique. A structure refinement of the distorted fcc phase of Pr using diffraction data collected with an imaging plate (IP) detector demonstrate that among some possible structures the rhombohedral structure with space group R3m best reproduces the observed diffraction pattern. The distorted fcc-fcc phase transition in La was observed as a function of the temperature at 23 GPa using a CCD-based detector. A five-minute exposure sufficiently long to measure the intensities of very weak superlattice reflections from the distorted fcc phase, which has been found to transform to the fcc phase at 550 K. The performance of the IP and a CCD-based detector are compared and their future developments discussed.

In situ X‐ray diffraction study of the phase transition from graphite to hexagonal diamond under high pressures and high temperatures

High pressure and high temperature in situ x‐ray diffraction experiments were carried out to study the phase transition from graphite to hexagonal diamond and the quenchability of hexagonal diamond to ambient conditions. When well crystallized graphite was compressed under quasi‐hydrostatic conditions, the phase transition to hexagonal diamond started at 18 GPa at room temperature, and this transition accelerated rapidly with increasing temperature. The hexagonal diamond formed at room temperature converted to graphite during the release of pressure, but when the sample was heated to more than 800 °C under high pressure, the hexagonal diamond phase became quenchable to ambient conditions. The observed 002 d‐spacing of the quenched hexagonal diamond is slightly larger than 111 d‐spacing of cubic diamond. Therefore, the c‐axis of hexagonal diamond is slightly expanded from an ideal structure based on the bond length in cubic diamond.

Formation and structure of iron hydride under the condition of the Earth’s interior

High pressure and high temperature in situ X‐ray diffraction studies on the systems of Fe‐H and Fe‐MgSiO3‐H2O were carried out to investigate the effect of water on the property of iron under the condition of the Earth’s interior. It was clarified that when water is added to the mixture of Fe and MgSiO3, then both FeHx and FeO are formed. Resulting FeHx has much lower melting temperature and has smaller density compared to those of pure iron. This reaction may affect a lot to the chemical composition and the formation process of the core.

Electrical conductivity and crystal structure of iron hydride under high pressure and high temperature

Electrical resistance and crystal structure of iron hydride were observed simultaneously under high pressure and high temperature using multi‐anvil type of high pressure apparatus. Various new phases of iron hydride were observed up to 1200 °C and 6 PGa. It was found that the temperature dependence of electrical resistance differs significantly from that of iron.