Search

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]

The discovery of superconductivity at 260 K in hydrogen-rich compounds like LaH10 re-invigorated the quest for room temperature superconductivity. Here, we report the temperature dependence of the upper critical fields μ0Hc2(T) of superconducting H3S under a record-high combination of applied pressures up to 160 GPa and fields up to 65 T. We find that Hc2(T) displays a linear dependence on temperature over an extended range as found in multigap or in strongly-coupled superconductors, thus deviating from conventional Werthamer, Helfand, and Hohenberg (WHH) formalism. The best fit of Hc2(T) to the WHH formalism yields negligible values for the Maki parameter α and the spin–orbit scattering constant λSO. However, Hc2(T) is well-described by a model based on strong coupling superconductivity with a coupling constant λ ~ 2. We conclude that H3S behaves as a strong-coupled orbital-limited superconductor over the entire range of temperatures and fields used for our measurements. The discovery of over 200 K superconductivity excites the community to search for room temperature superconductivity. Here, Mozaffari et al. report the temperature dependence of the upper critical fields of superconducting H3S under a record-high combination of pressures up to 160 GPa and magnetic fields up to 65 T. [ABSTRACT FROM AUTHOR]

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]

We investigated the phase transformation of hot dense fluid hydrogen using static high-pressure laser-heating experiments in a laser-heated diamond anvil cell. The results show anomalies in the heating efficiency that are likely to be attributed to the phase transition from a diatomic to monoatomic fluid hydrogen (plasma phase transition) in the pressure range between 82 and 106 GPa. This study imposes tighter constraints on the location of the hydrogen plasma phase transition boundary and suggests higher critical point than that predicted by the theoretical calculations. [ABSTRACT FROM AUTHOR]

The pressure dependence of the superconducting transition temperature (Tc) and unit cell metrics of tetragonal (NH3)yCs0.4FeSe were investigated in high pressures up to 41 GPa. The Tc decreases with increasing pressure up to 13 GPa, which can be clearly correlated with the pressure dependence of c (or FeSe layer spacing). The Tc vs. c plot is compared with those of various (NH3)yMxFeSe (M: metal atoms) materials exhibiting different Tc and c, showing that the Tc is universally related to c. This behaviour means that a decrease in two-dimensionality lowers the Tc. No superconductivity was observed down to 4.3 K in (NH3)yCs0.4FeSe at 11 and 13 GPa. Surprisingly, superconductivity re-appeared rapidly above 13 GPa, with the Tc reaching 49 K at 21 GPa. The appearance of a new superconducting phase is not accompanied by a structural transition, as evidenced by pressure-dependent XRD. Furthermore, Tc slowly decreased with increasing pressure above 21 GPa, and at 41 GPa superconductivity disappeared entirely at temperatures above 4.9 K. The observation of a double-dome superconducting phase may provide a hint for pursuing the superconducting coupling-mechanism of ammoniated/non-ammoniated metal-doped FeSe. [ABSTRACT FROM AUTHOR]

Abstract: Pure boron has two allotropes of -rhombohedral boron (-boron) and -rhombohedral boron (-boron) based on icosahedral clusters unit. Pressure-induced metallization and superconductivity of -boron was already reported at pressures above 160GPa. Here we investigate the electrical properties of -boron at Mbar (100GPa) pressure and low temperature. At room temperature the electrical resistivity of -boron decreased with 5 orders by applying pressures up to 160GPa. The temperature dependence of the electrical resistivity recorded at around 160GPa showed superconducting transition at 6K. [ABSTRACT FROM AUTHOR]

Adv. Energy Mater. 2024, 14, 2400077DOI: 10.1002/aenm.202400077In the phrase "D.S. and D.Z. thank the National Natural Science Foundation of China (NSFC, grant No. 1231101238)..." of the Acknowledgements section, the NSFC grant number was incorrect. The correct NSFC grant number is 12350410354.The authors apologize for this error.By Di Zhou; Dmitrii Semenok; Michele Galasso; Frederico Gil Alabarse; Denis Sannikov; Ivan A. Troyan; Yuki Nakamoto; Katsuya Shimizu and Artem R. OganovReported by Author; Author; Author; Author; Author; Author; Author; Author; Author [Extracted from the article]

We report the pressure dependence of electrical resistance R(T) of a frustrated pyrochlore oxide Nd2Ir2O7, which shows a second-order metal-insulator transition (MIT) at 36 K. This MIT is monotonically suppressed by the application of pressure. The insulating phase disappears at around 10 GPa. Then, in the pressure-induced metallic state above 10 GPa, a new pressure-induced phase transition emerges at around 3 K, which is characterized by a resistance drop. The new phase transition is due to a ferromagnetic (FM) ordering, which is suggested to be an ordered spin ice (two-in two-out) state of the Nd moment via the RKKY interaction. We succeeded in observing the phase competition between the MIT and the FM ordering by the application of high pressure. [ABSTRACT FROM AUTHOR]

Abstract: We have measured the electrical resistance of (Mg0.9Fe0.1)SiO3 perovskite with increasing pressure in a diamond-anvil cell (DAC). Results demonstrate that the electrical conductivity increased with pressure to about 70GPa, then conversely decreased to around 85GPa, and again increased mildly to 135GPa. As inferred from the previous studies of (Mg,Fe)O ferropericlase, the observed reduction in the conductivity of perovskite at 70–85GPa is most likely due to the high-spin to low-spin transition of iron; it decreases the number of unpaired electrons and therefore diminishes the conduction by electron hopping between the ferric and ferrous iron sites. Present conductivity data provide valuable implications for the pressure range of spin transition in (Mg,Fe)SiO3 perovskite, which has been highly controversial. The relatively abrupt reduction in the electrical conductivity above 70GPa is reconciled with the spin-pairing transition in ferric iron, which may occur rather sharply at this pressure range. [Copyright &y& Elsevier]

The crystallographic structure of anthracene is studied under high pressure up to 27 GPa using diamond anvil cells. Different pressure-transmitting media (helium, a methanol–ethanol mixture, a normal- and iso-pentane mixture and no medium) were used up to specific critical pressures where the hydrostatic conditions are lost. It is clearly observed that the loss of hydrostaticity is associated with a crystallographic phase-transition in anthracene. The phase-transition is observed as reversible, and it is accompanied by a large hysteresis. These observations clarify conflicting reports in the literature on the high-pressure phase-transition of anthracene. [Copyright &y& Elsevier]

Abstract: X-ray powder diffraction study of PbHPO4 was carried out under hydrostatic conditions at room temperature. We could not detect any difference in the diffraction patterns except peak shift with increasing pressures up to 6GPa. By further compression, a new pressure-induced phase appears at about 6.5GPa. We have determined that the structure of this high-pressure phase has a possible space group of Pmmm, and which is stable up to 17GPa. During decompression process, this phase is converted back to the original phase II at 0.7GPa. [Copyright &y& Elsevier]

Here we report on the effects of material strength factors on the generation of surface structure due to nonuniform laser irradiation. The influence of material strength on the generation of perturbation on a diamond surface subjected to nonuniform laser irradiation was experimentally investigated. Our previous investigations suggested that stiffer and denser materials reduce surface perturbation due to spatially nonuniform laser irradiation, which was reproduced well by calculations with multi-dimensional hydrodynamic simulation code. In this work, we found that local fractures due to yield strength failure are generated by high degrees of irradiation non-uniformity. A characteristic crack-like surface structure was observed, which was not reproduced by the 2D simulation code calculations at all. The 2D simulations showed that the pressure at the diamond surface locally exceeds the Hugoniot elastic limit due to nonuniform irradiation, implying the potential for development of surface perturbations. We also measured the areal-density distribution of perturbations for single-crystal diamond and diamond with a thin high atomic number (high-Z) coating on its surface. The experimental results imply that the combination of a stiff material and thin high-Z coating can suppress the solid-strength effects caused by large irradiation non-uniformity. The knowledge given here is applicable to inertial confinement fusion target design, laser material processing, and universal problems involving solids and high-energy-density plasmas. [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]

Highlights • DDR-type zeolite membrane with excellent CO 2 permselectivity was successfully developed. • The membrane durability was confirmed by 140 hrs gas permeation testing up to 8 MPa G. • Importance of high CO 2 permselective membrane was indicated for a CO 2 -EOR project. Abstract JGC Corporation (JGC) and NGK Insulators, Ltd. (NGK) have been developing the world's largest DDR-type zeolite membrane to meet the practical needs of CO 2 /hydrocarbon separation in the natural gas and CO 2 Enhanced Oil Recovery (CO 2 -EOR) industries. DDR-type zeolite has desirable nano-size pores for CO 2 /hydrocarbon separation. NGK has developed a thin, defect-free DDR-type zeolite membrane with a monolithic structure. This membrane is prepared onto the inner surface of a cylindrical monolithic alumina substrate having 30 channels with a diameter and length of 30 mm and 160 mm, respectively. CO 2 permselectivity over CH 4 of the monolithic membrane was investigated using the binary gas mixture of 61–67 mol% CO 2 and 33–39 mol% CH 4 at 44–46 °C with up to 8.0 MPa G as the feed pressure. The CO 2 permeability reached 1973 Barrer (6.6 × 10−13 mol m m−2 s−1 Pa−1) while the separation factor of CO 2 /CH 4 exceeded 140 at the transmembrane pressure difference of 2.5 MPa. This CO 2 permeability decreased to 1154 Barrer (3.9 × 10−13 mol m m−2 s−1 Pa−1) at the transmembrane pressure difference of 7.0 MPa; however, the separation factor of CO 2 /CH 4 was still as high as 90. In order to understand the stability of the monolithic membrane, the change in the permeability of CO 2 and CH 4 with time was measured at 58–60 °C with transmembrane pressure difference of 7.4–7.7 MPa using the binary gas mixture of 65–71 mol% CO 2 and 29–35 mol% CH 4 for 140 h. During the gas permeation test, the CO 2 permeability was almost constant while CH 4 permeability slightly decreased. As a result, the separation factor of CO 2 /CH 4 was maintained at the initial value. Based on the experimental results, we evaluated the potential applicability of the DDR-type zeolite membrane compared to the conventional polymer membrane for a CO 2 recovery process in a CO 2 -EOR project where CO 2 is often separated from the associated gas for re-use. We assumed that the associated gas contains 70 mol% CO 2 and 30 mol% CH 4 at a pressure of 4.0 MPa G while the specification of CO 2 purity in the permeate gas was 95 mol% at a pressure of 0.3 MPa G. When this associated gas is treated using a single-stage membrane process, only 49% of CO 2 was recovered by a membrane having a CO 2 /CH 4 separation factor of 12.5 like a typical polymer membrane. On the other hand, membranes having CO 2 /CH 4 separation factors of 80–100 could recover 98–99% of CO 2 while more than 96 mol% purity of CH 4 was obtained at the retentate side. This simulation study indicated that the highly selective membrane like the DDR-type zeolite membrane can recover not only high purity CO 2 for CO 2 -EOR projects, but also make available CH 4 for use or sale. This high purity CH 4 brings additional benefit to the CO 2 -EOR operators. [ABSTRACT FROM AUTHOR]

Polyhydrides of alkali metals under high pressures have been attracting great interests owing to the predicted pressure-stabilized untraditional stoichiometries and potential superconductivity. We have performed Raman scattering measurements of lithium polyhydrides synthesized under high pressure and high temperature conditions up to 182 GPa. Between 30 and 180 GPa, four phases appear, and they are tentatively named α (30-140 GPa), β (30-90 GPa), γ (90-140 GPa), and δ (140 GPa) phase. By observing the H2 vibrons at higher wavenumbers than pure H2 and their pressure dependence, it was revealed that the α phase contains electrically neutral H2 in its crystal lattice without electron transfer from Li atoms. The comparisons with H2-containing rare gas compounds Ar(H2)2, Kr(H2)4, and Xe(H2)8 suggest that a H2 molecule is surrounded by six to eight neighboring H2 molecules in the α phase. On the other hand, the Raman spectra of the β, γ, and δ phases suggest that they contain the elongated H2 that is negatively charged by the electron transferred from the surrounding matrices. All the α, β, γ, and δ phases were found to remain transparent insulators at pressures below 182 GPa. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Metal intercalation to graphite produces various types of superconductors. The highest superconducting transition temperature T c (onset temperature, T c onset , of 11.5 K) was found in Ca intercalated graphite, denoted CaC 6 . T c onset increased up to 15.1 K at 7.5 GPa, implying a positive pressure dependence. However, no new metal-intercalated graphite superconductors with T c onset higher than 11.5 K at ambient pressure have so far been reported. To search for new graphite superconductors, we successfully synthesized binary-element-intercalated graphite, Ca x K 1−x C y . Their structure resembles that of KC 8 . T c increased continuously with increasing x. Furthermore, the pressure dependence of T c in Ca 0.6 K 0.4 C 8 was investigated over a wide pressure range from 0–43 GPa. T c (= 9.6 K at 0 GPa) increased to 11.6 K at 3.3 GPa, and decreased to 2.0 K at 41 GPa. This behavior is similar to that of CaC 6 , albeit with a lower maximum T c . X-ray diffraction patterns were measured under high pressures of 0–24 GPa, and suggest a structural transition at 15 GPa. Evidence is given for superconducting graphite involving binary metal intercalation. [ABSTRACT FROM AUTHOR]

We have studied the superconducting properties of CeTIn5 (T=Rh, Ir) under high pressures by means of electrical resistivity measurements and determined the pressure–temperature phase diagrams for the superconducting transition. For both systems, the superconductivity exists in a wide pressure range, 1.5⩽P⩽6.5 GPa for CeRhIn5 and 0⩽P⩽5.2 GPa for CeIrIn5. [Copyright &y& Elsevier]

‘Aromatic hydrocarbon’ implies an organic molecule that satisfies the (4 n + 2) π-electron rule and consists of benzene rings. Doping solid aromatic hydrocarbons with metals provides the superconductivity. The first discovery of such superconductivity was made for K-doped picene (K x picene, five benzene rings). Its superconducting transition temperatures ( T c ’s) were 7 and 18 K. Recently, we found a new superconducting K x picene phase with a T c as high as 14 K, so we now know that K x picene possesses multiple superconducting phases. Besides K x picene, we discovered new superconductors such as Rb x picene and Ca x picene. A most serious problem is that the shielding fraction is ⩽15% for K x picene and Rb x picene, and it is often ∼1% for other superconductors. Such low shielding fractions have made it difficult to determine the crystal structures of superconducting phases. Nevertheless, many research groups have expended a great deal of effort to make high quality hydrocarbon superconductors in the five years since the discovery of hydrocarbon superconductivity. At the present stage, superconductivity is observed in certain metal-doped aromatic hydrocarbons (picene, phenanthrene and dibenzopentacene), but the shielding fraction remains stubbornly low. The highest priority research area is to prepare aromatic superconductors with a high superconducting volume-fraction. Despite these difficulties, aromatic superconductivity is still a core research target and presents interesting and potentially breakthrough challenges, such as the positive pressure dependence of T c that is clearly observed in some phases of aromatic hydrocarbon superconductors, suggesting behavior not explained by the standard BCS picture of superconductivity. In this article, we describe the present status of this research field, and discuss its future prospects. [ABSTRACT FROM AUTHOR]

Pressure-induced stacking sequence variations of gold are predicted from first-principles calculations. At the static condition, the ABC stacking in the face-centered-cubic (fcc) phase changes into ABCACB above at least 200 GPa, and then into ABAC corresponding to the double hexagonal-close-packed structure. By further compression, the hexagonal-close-packed (hcp) structure with the AB stacking emerges as the most stable structure of all the stacking structures. This sequence of the transitions shows a step-by-step increase of the hexagonality over a wide pressure range. The calculations of phonon free energy indicate that the stable region of the intermediate stacking structures between fcc and hcp such as ABCACB or ABAC gets to be narrow with increase of temperature and fcc directly transforms into hcp above 400 K. This direct transition from fcc to hcp is qualitatively consistent with the earlier experimental observations. [ABSTRACT FROM AUTHOR]

The recently discovered high pressure phase VII of calcium [M. Sakata et al, Phys. Rev. B 83,220512(R) (2011)] has the highest superconducting transition temperature (Tc) of 29 K among all the elements. Understanding the cause for such a high Tc state is necessary to clarify its crystal structure. The structure of this phase was determined by an x-ray powder diffraction experiment and a density functional theory calculation and was not found to be the usual host-guest type but consisted of a 2 × 2 supercell in the tetragonal ab plane with a commensurate host-guest ratio of 4/3 along the c axis containing 128 atoms. [ABSTRACT FROM AUTHOR]