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Both micro-paired and conical support type double-stage diamond anvil cells (ds-DAC) were tested using a newly synthesized ultra-fine nano-polycrystalline diamond (NPD). Well-focused X-ray sub-micron beam and the conically supported 2nd stage anvils (micro-anvils) with 10 μm culet enable us to obtain good quality X-ray diffraction peaks from the sample at around 400 GPa. The relationship between confining pressure and sample pressure depends heavily on the initial height (thickness) of micro-anvils, the difference of a few micrometers leads to a quite different compression path. The conical support type is a solution to retain both enough thickness and strength of micro-anvils at higher confining pressure conditions. All conical support ds-DAC experiments terminated by the failure of the 1st stage anvil instead of 2nd one. The combination of ultra-fine NPD 2nd stage anvil and NPD 1st stage anvil opens a new frontier for measurement of the X-ray absorption spectrum above 300 GPa. [ABSTRACT FROM AUTHOR]

We present two distorted face-centered cubic (dfcc) structures of yttrium under high pressure, which have been found by a first-principles genetic algorithm technique. The structures are a tetragonalP43(dfcc-I) and a triclinicP1¯ (dfcc-II), formed by slight distortions from a trigonalR3¯mstructure reported as the dfcc phase earlier. The enthalpy difference between the two dfcc structures is less than 0.2 mRy/atom, and dfcc-I is marginally more stable than dfcc-II in lower pressure region. The enthalpy comparison among candidate structures indicates the structural phase transitions into dfcc-I at 41 GPa, into dfcc-II at 81 GPa, and into an orthorhombicFdddstructure at 106 GPa. [ABSTRACT FROM PUBLISHER]

Metallization of solid iodine has carefully been investigated using X-ray diffraction (XRD) measurements, electrical resistance measurements, andab initiocalculations based on the density functional theory. The XRD and electrical resistance measurements have clarified that iodine takes the insulator-to-metal transition at 14–16 GPa in the diatomic molecular solid phase. Theab initiocalculations have predicted that the electronic band gap decreases monotonically with increasing pressure, and it completely closes at around 11–12 GPa in the molecular phase, which is consistent with the experimental observations. At the metallization, we also experimentally and theoretically found the anomaly in the decrease of lattice constants along with pressurization. [ABSTRACT FROM AUTHOR]

We present the first successful in situ simultaneous measurement of the electrical resistance and X-ray diffraction of FeHx (x∼ 1) under high-pressure H2 up to 25.5 GPa and low temperatures down to 9 K. The electrical resistivity ρ showed a sharp increase with the formation of iron-hydride FeHx (x∼ 1) at 3.5 GPa. The ε'-phase of FeHx was found to be metallic up to 25.5 GPa. The ρ vs. T curves up to 16.5 GPa approximately follow Fermi-liquid law below 25 K. However, T5 was found to be better fitting at 25.5 GPa. This change can be considered to be related to the previously reported ferromagnetism collapse at corresponding pressure. [ABSTRACT FROM AUTHOR]