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A new method for synthesis of metal polyhydrides via high‐pressure thermal decomposition of corresponding amidoboranes in diamond anvil cells is proposed. Within this approach, molecular semiconducting cesium (P4/nmm‐CsH7, P1‐CsH15+x) and rubidium (RbH9‐x) polyhydrides with a very high hydrogen content reaching 93 at.% are synthesized. Preservation of CsH7 at near ambient conditions, confirmed both experimentally and theoretically, represents a significant advance in the stabilization of hydrogen‐rich compounds. In addition, two crystalline modifications of RbH9‐x with pseudohexagonal and pseudotetragonal structures identified by synchrotron X‐ray diffraction, and Raman measurements are synthesized. Both phases are stable at 8–10 GPa. This is an unprecedentedly low stabilization pressure for polyhydrides. These discoveries open up possibilities for modifying existing hydrogen storage materials to increase their efficiency. [ABSTRACT FROM AUTHOR]

Electrical resistivity measurements on oriented FeTiO3 ilmenite using single crystals at high pressures proves that FeTiO3 ilmenite shows anisotropic electrical resistivity. The resistivity in the direction perpendicular to the c-axis decreased monotonously with increasing pressure. In contrast, the resistivity in the parallel direction to the c-axis initially decreased and slightly increased with increasing pressure above 6 GPa. It then resumed decreasing above 8 GPa. The hallow-shape of the curvature was observed. Neutron and synchrotron X-ray diffraction experiments provided an accurate picture of the pressure-induced changes of the FeTiO3 ilmenite structure. FeTiO3 transforms neither into perovskite nor LiNbO3 phase under pressures up to 28 GPa. However, different compression curves were observed for both FeO6 and TiO6 octahedra below 8 GPa. FeO6 is more compressible and flexible than TiO6. Among Fe–Fe, Ti–Ti and Fe–Ti interatomic distances, the shortest Fe–Ti distance presents the highest electrical restivity and electron mobility according to Fe2+Ti4+ and Fe3+Ti3+ by electron super-exchange mechanism, which is enhanced during compression. At high pressure, the electron configuration of Fe2+ (3d6) is more strongly changed than Ti4+ (3d0) and the former cation is the emphasized by Jahn–Teller effect in the ligand field of C3v molecular symmetry. The anisotropic electrical resistivity and non-uniform structure change of Fe–Ti interatomic distance can be explained by possible spin transition. The spin transition of FeKβ from high-spin to intermediate-spin state is possible in the electronic state change of FeTiO3. [ABSTRACT FROM AUTHOR]

Author(s): Kenji Ohta (corresponding author) [1]; Yasuhiro Kuwayama [2]; Kei Hirose [3, 4]; Katsuya Shimizu [5]; Yasuo Ohishi [6] Earth continuously generates a dipole magnetic field in its convecting liquid [...]

A sharp focus of current research on superconducting superhydrides is to raise their critical temperature Tc at moderate pressures. Here, we report a discovery of giant enhancement of Tc in CeH9 obtained via random substitution of half Ce by La, leading to equal-atomic (La,Ce)H9 alloy stabilized by maximum configurational entropy, containing the LaH9 unit that is unstable in pure compound form. The synthesized (La,Ce)H9 alloy exhibits Tc of 148–178 K in the pressure range of 97–172 GPa, representing up to 80% enhancement of Tc compared to pure CeH9 and showcasing the highest Tc at sub-megabar pressure among the known superhydrides. This work demonstrates substitutional alloying as a highly effective enabling tool for substantially enhancing Tc via atypical compositional modulation inside suitably selected host crystal. This optimal substitutional alloying approach opens a promising avenue for synthesis of high-entropy multinary superhydrides that may exhibit further increased Tc at even lower pressures.Superconductivity was recently discovered in the clathrate hydride CeH9 with superconducting temperature (Tc) of 57 K at pressures below 1 megabar. Here, the authors show that Tc can be increased to 148 K in the substitutional alloy (La,Ce)H9, while maintaining a pressure below 1 megabar. [ABSTRACT FROM AUTHOR]

Lithium, the lightest metal, has long been considered to have a 'simple' electronic structure that can be well explained within the nearly-free-electron model. But lithium does not stay 'simple' under compression: rather than becoming more free-electron-like as pressure is increased, first-principles calculations (1,2) suggest that it transforms into a semi-metal or semiconductor. Experimentally, it has been shown that dense lithium adopts low-symmetry structures (3,4); there is also evidence that its resistivity increases with pressure (5-8).However, the electronic transport properties of lithium have so far not been directly monitored as a function of increasing static pressure. Here we report electrical resistance measurements on lithium in a diamond anvil cell up to pressures of 105 GPa, which reveal a significant increase in electrical resistivity and a change in its temperature dependence near 80 GPa. Our data thus provide unambiguous experimental evidence for a pressure-induced metal-to-semiconductor transition in a 'simple' metallic element., Ever since it was predicted (1,2) that the light alkali metal lithium (Li) may form pairs of atoms ('dimers') and transform to a semi-metal or semiconductor in its highly compressed [...]

At pressures above one million atmospheres (100 GPa), oxygen becomes a shining metal, and moreover, it exhibits superconductivity. In this study, we have investigated the material properties at high pressures, focusing on the change in the crystal structure and appearance of superconductivity. We use a high-pressure device, diamond anvil cell (DAC) and we develop technology for superconductivity detection. One of the goals of this high-pressure research is to realize the metallic hydrogen accompanied by the room temperature superconductivity. The recently discovered hydride superconductors with the transition temperatures exceeding 200 K is a significant example achieved in high-pressure technologies. [ABSTRACT FROM AUTHOR]

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]

In this study, we performed electrical resistance measurements for a superconductive H3S synthesized from elemental sulfur and hydrogen (2S + 3H2 → 2H3S). The H3S was synthesized by heating a piece of sulfur in solid hydrogen at 150 GPa. Powder X-ray diffraction (XRD) studies using a synchrotron X-ray revealed that the synthesized H3S possessed a considerably improved crystalline quality and no residual sulfur compared to the H3S synthesized from H2S. Further, a superconducting transition with a sharp drop of resistance at \(T_{\text{c}}^{\text{onset}} = 200\) K was observed in resistance measurements at low temperature, and the highest \(T_{\text{c}}^{\text{offset}}\) of 186 K was obtained in H3S. [ABSTRACT FROM AUTHOR]