We have developed a new 6-axis apparatus in which movement of the six anvils are controlled by the high-tech servo mechanism. It is possible to keep the Kawai cell cubic within accuracy of ± 2 µm during compression and decompression. Pressures up to ca. 60 GPa have been generated by using sintered diamond cubic anvils with 14 mm edge length and 1.5 mm truncation. Comparison of the results with our previous experiments using the DIA-type press demonstrates that significant amount of applied load is lost by friction in squeezing the Kawai-cell by the DIA-type press. The load loss increases with increasing load, and it amounts to 45% of the applied load when compressed up to ca. 6.2 MN.
GSECARS (GeoSoilEnviroCARS, the University of Chicago) operates a bending magnet and an undulator beamlines at Sector 13, Advanced Photon Source. Experimental technique for High Pressure X-ray Tomographic Microscope (HPXTM) using monochromatized X-rays has been developed. The module for HPXTM also has shear deformation capability, which enables us to perform HPXTM experiments for microstructure developed by shear deformation under high pressure. A combination of Deformation DIA (D-DIA) and monochromatic X-rays has been developed for quantitative deformation experiments under pressure above 10 GPa. Deformation experiments of ε-iron was performed at pressures up to 19 GPa and temperatures up to 700 K.
In this article, recent technical developments in high-pressure deformation experiments especially in the field of Earth science are reviewed. The diamond anvil cell has an advantage in performing deformation experiments at very high pressures (up to 160 GPa) compared to other large-volume apparatuses. However, diamond anvil cell has severe limitation in quantitative strain measurements, deformation at high temperatures and deformation with large strain. On the other hand, quantitative rheological measurements at relatively high pressures (up to 10-20 GPa) and high temperatures (up to 1000-2000 K) are possible by using recently developed large-volume deformation apparatuses, rotational Drickamer apparatus, deformation-DIA and “big D-DIA”. Synchrotron X-ray is a powerful tool for in-situ strain and stress measurements in high-pressure deformation experiments using these apparatuses.
Effects of pressure on the physical properties are very important for understanding highly correlated electron systems, in which pressure-induced attractive phenomena such as superconductivity and magnetically ordered non-Fermi liquid have been observed. Up to now, many scientists have developed a lot of high pressure apparatus for each purpose. In this paper, we present the very small “palm cubic-anvil high-pressure apparatus” for precise electric transport measurements under high pressure up to 8 GPa. The most outstanding characteristic of this pressure cell is its compactness. This cell enables us to measure absolute values of electrical resistivity, magneto-resistance and Hall coefficient at various temperatures. The details of our palm cubic high-pressure apparatus are introduced, and some neutron experimental results at room temperature are discussed.
Two post-perovskite oxides were discussed. One is CaPtO3, which is a new analog to the isostructural MgSiO3. By analyzing structural parameters, we elucidate the role of covalency in the post-perovskite compounds. The other is a new solid solution Ca1-xNaxIrO3 (0 ≤ x ≤ 0.37). This system exhibits a filling-control metal-insulator transition on a quasi-two-dimensional lattice. These studies indicate that the post-perovskite structure is an excellent playground to search novel electronic phases of strongly correlated electrons.
X-ray diffraction (XRD) measurement in radial geometry using a diamond anvil cell (DAC) and synchrotron radiation is a powerful tool to investigate lattice preferred orientations (LPO) of high-pressure materials such as post-perovskite (PPv) -type phases. Recent experimental and theoretical reports about LPO of PPv-type phases and problems of deformation experiments were reviewed in this article. Our results of radial and axial XRD measurements and deformation experiments on MgGeO3-PPv were shown also. When the MgGeO3-PPv was formed in DAC, it had strong LPO from the beginning even before making the plastic deformation and the LPO changed depending on the pre-phase before the transformation. Pressure variation of axial diffraction patterns of MgGeO3-PPv during plastic deformation were obtained for the first time by using a diamond gasket technique.
Transformation from perovskite to post-perovskite was observed in MnGeO3 and MgGeO3 in the Kawai-type apparatus equipped with sintered diamond anvils by means of in situ X-ray diffraction method. In MnGeO3, post-perovskite phase was observed at 63.5 GPa and 1233 K. The transition pressure was ∼ 6 GPa higher than previous report by the laser heated diamond anvil cell experiment. In MgGeO3, we observed the transformation from perovskite to post-perovskite and the reversal transformation under the conditions of 61-64 GPa and 1100-1700 K. The phase boundary was determined to be P (GPa) = 5.2×10-3T (K)+55.2, where P is pressure and T is absolute temperature, which is almost consistent with previous result by diamond anvil experiments. However, reliable pressure standard is needed to determine the boundary precisely.
Recently we have measured the electrical conductivity of (Mg0.9Fe0.1)SiO3 perovskite and post-perovskite at high pressure and temperature in a laser-heated diamond-anvil cell (DAC). The results demonstrate that the conductivity of post-perovskite is > 102 S/m, higher by three orders of magnitude than that of perovskite at similar pressure range, and does not vary greatly with temperature. The highly conductive post-perovskite layer above the core-mantle boundary would, by electromagnetic coupling, enhance the exchange of angular momentum between the fluid core and solid mantle, which can explain the observed changes in length of a day on decadal timescales. Heterogeneity in the conductivity of the lowermost mantle is likely to depend on changes in chemistry of the boundary region, not fluctuations in temperature.
High-pressure fluorescence study on the bilayer phase behavior of symmetric and asymmetric phospholipids in my doctoral thesis is briefly reviewed. It has been clarified by the novel analysis of the second derivatives of fluorescent spectra that the fluorescent probe Prodan resides multiple sites in the bilayer membrane of phosphatidylcholines (PCs) depending on the membrane states. Comparing the diagrams of three dimensional fluorescent spectra among them, the present results revealed that the slight difference in acyl chain length between the sn-1 and sn-2 positions in the PC molecules provides significant influence on their bilayer phase behavior, especially in the bilayer interdigitation.
The highly compressed state of metal hydride has been investigated to explore structural and electronic transitions characteristic to hydride. The hydrogen atoms play the lead in the transitions, showing displacement in or transfer between the interstitial sites of a metal lattice. One example is the band gap closing observed for a long period lattice of yttrium tri-hydride, YH3, appearing at pressures above 12 GPa. Another example is photochromic event observed again for yttrium hydride, YHx. The former is likely accompanied by the in-site displacement of hydrogen atoms and the latter by the site-to-site transfer.