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Finding high‐temperature superconductivity in light‐weight element containing compounds at atmosphere pressure is currently a research hotspot but has not been reached yet. Here it is proposed that hard or superhard materials can be promising candidates to possess the desirable high‐temperature superconductivity. By studying the electronic structures and superconducting properties of H and Li doped c‐BN within the framework of the first‐principles, it is demonstrated that the doped c‐BN are indeed good superconductors at ambient pressure after undergoing the phase transition from the insulating to metallic behavior, though holding different nature of metallization. Li doped c‐BN is predicted to exhibit the superconducting transition temperature of ≈58 K, while H doped c‐BN has stronger electron–phonon interaction and possesses a higher transition temperature of 122 K. These results and findings thus point out a new direction for exploring the ambient‐pressure higher‐temperature superconductivity in hard or superhard materials. [ABSTRACT FROM AUTHOR]

The reactivity between NaH and H2 has been investigated through a series of high-temperature experiments up to pressures of 78 GPa in diamond anvil cells combined with first principles calculations. Powder X-ray diffraction measurements show that heating NaH in an excess of H2 to temperatures around 2000 K above 27 GPa yields sodium trihydride (NaH3), which adopts an orthorhombic structure (space group Cmcm). Raman spectroscopy measurements indicate that NaH3 hosts quasi-molecular hydrogen (H2-) within a NaH lattice, with the H2- stretching mode downshifted compared to pure H2 (Av 120 cm-1 at 50 GPa). NaH3 is stable under room temperature compression to at least 78 GPa, and exhibits remarkable P-T stability, decomposing at pressures below 18 GPa. Contrary to previous experimental and theoretical studies, heating NaH (or NaH3) in excess H2 between 27 and 75 GPa does not promote further hydrogenation to form sodium polyhydrides other than NaH3. [ABSTRACT FROM AUTHOR]

To explore carbide superconductors with higher transition temperature, two novel carbon structures of cage‐network are designed and their superconductivity is studied by doping metals. MC6 and MC10 are respectively identified as C24 and C32 cage‐network structures. This study finds that both carbon structures drive strong electron–phonon interaction and can exhibit superconductivity above liquid nitrogen temperature. Importantly, the superconducting transition temperatures above 100 K are predicted to be achieved in C24‐cage‐network systems doped by Na, Mg, Al, In, and Tl at ambient pressure, which is far higher than those in graphite, fullerene, and other carbides. Meanwhile, the superconductivity of cage‐network carbides is also found to be sensitive to the electronegativity and concentration of dopant M. The result indicates that the higher transition temperatures can be obtained by optimizing the carbon‐cage‐network structures and the doping conditions. The study suggests that the carbon‐cage‐network structure is a direction to explore high‐temperature superconducting carbides. [ABSTRACT FROM AUTHOR]

In individuals with underlying chronic liver disease (CLD), hepatitis E virus (HEV) infection is a potential trigger of acute‐on‐chronic liver failure. In this systematic review, seven electronic databases were searched. Pooled incidence rates with 95% confidence intervals (95% CIs) were calculated by the Freeman–Tukey double arcsine transformation method. The association between death or liver failure and HEV superinfection in CLD patients was estimated by the odds ratios (OR) with a 95% CI. A total of 18 studies from 5 countries were eligible for systematic review. The prevalence of acute HEV infection in hospitalized CLD patients with clinical manifestations of hepatitis was 13.6%, which was significantly higher than that in CLD patients from the community (pooled prevalence 1.1%). The overall rates of liver failure and mortality in CLD patients with HEV superinfection were 35.8% (95% CI: 26.7%–45.6%) and 14.3% (95% CI: 10.6%–18.5%), respectively, with the rates in cirrhotic patients being approximately 2‐fold and 4‐fold higher than those in noncirrhotic patients, respectively. The risks of liver failure (OR = 5.5, 95% CI: 1.5–20.1) and mortality (OR = 5.0, 95% CI: 1.9–13.3) were significantly higher in CLD patients with HEV superinfection than in those without HEV superinfection. HEV testing in hospitalized CLD patients is necessary due to the high prevalence of HEV infection observed in hospitalized CLD patients. HEV superinfection could accelerate disease progression in patients with underlying CLD and increase mortality in these patients. HEV vaccination is appropriate for patients with pre‐existing CLD. [ABSTRACT FROM AUTHOR]

Using first-principles calculations based on density functional perturbation theory, we demonstrate hydrogenation-induced superconductivity in monolayer TiB2H. Hydrogen adatoms destroy the Dirac state of monolayer TiB2 and monolayer TiB2H has a high vibration frequency. Monolayer TiB2H is a phonon-mediated superconductor. Monolayer TiB2H has a predicted T c of 8 K, which further increases under external tensile strain. Thus, this study extends our understanding of superconductivity in two-dimensional (2D) materials and its potential applications. [ABSTRACT FROM AUTHOR]

To explore the high-temperature superconductor at low pressures, we have investigated the crystal structures, electronic properties, and possible superconductivity in the case of methane (CH4) doped by lithium in the pressure range of 0 − 1 0 0 GPa, based on the first-principles calculations. The results show that Li-intercalated CH4 (Lix(CH4) 1 − x ) can realize metallization and superconductivity at low pressures, even 5 GPa. We find that there is a charge transfer between Li and CH4, but the metallization is driven by the change of crystal field induce by doping instead of charge transfer. The critical temperture is predicted from 3.8 K at 5 GPa for LiCH4 to 12.1 K at 100 GPa for Li(CH4)4. The low-pressure superconductivity of Lix(CH4) 1 − x can be further optimized by adjusting component and pressure. [ABSTRACT FROM AUTHOR]

Both the vibrational and structural properties of coronene have been investigated upon compression up to 30.5 GPa at room temperature by a combination of Raman scattering and synchrotron x-ray diffraction measurements. The spectroscopic and crystallographic results demonstrate that two pressure-induced structural phase transitions take place at 1.5 GPa and 12.2 GPa where the high-pressure phases are identified as monoclinic and orthorhombic crystal structures with space groups of P2/m and Pmmm, respectively. A kink in the slope of the cell parameters as a function of pressure is associated with the disappearance of several internal Raman modes, which suggests the existence of structural distortions or reorganizations at approximately 6.0 GPa. Above 17.1 GPa, almost no evidence of crystallinity can be observed, indicating a possible transformation of coronene into an amorphous phase. [ABSTRACT FROM AUTHOR]

The structural and vibrational properties of phenanthrene are measured at high pressures up to 30.2 GPa by Raman spectroscopy and synchrotron X-ray diffraction techniques. Two phase transitions are observed in the Raman spectra at pressures of 2.3 GPa and 5.4 GPa which correspond to significant changes of intermolecular and intramolecular vibrational modes. Above 10.2 GPa, all the Raman peaks are lost within the fluorescence background; however, upon further compression above 20.0 GPa, three broad peaks are observed at 1600, 2993, and 3181 cm-1, indicating that phenanthrene has transformed into amorphous phase. Using X-ray diffraction, the structures of corresponding phases observed from Raman spectra are indexed with space groups of P21 for phase I (0-2.2 GPa), P2/m for phase II (2.2-5.6 GPa), P2/m+Pmmm for phase III (5.6-11.4 GPa) which has a coexistence of structures, and above 11.4 GPa the structure is indexed with space group of Pmmm. Although phenanthrene has transformed to a hydrogenated amorphous carbon structure above 20.0 GPa, these amorphous clusters still show characteristic crystalline behavior based on our X-ray diffraction patterns. Our results suggest that the long-range periodicity and the local disorder state coexist in phenanthrene at high pressures. [ABSTRACT FROM AUTHOR]

To find potential alkaline-earth metal-doped aromatic superconductors and clarify the origin of superconductivity in metal-doped phenanthrene (PHN) systems, we have systematically investigated the crystal and electronic structures of bivalent metal (Mg, Ca, Sr and Ba)-doped PHNs by first-principles calculations. The results show that only Ba1.5PHN can satisfy the conditions of both thermodynamic stability and metallization. We predicted that Ba1.5PHN is superconducting with the critical temperature of 5.3 K. Based on the metal atomic radius and electronegativity and combined with monovalent metal- and trivalent metal-doped PHNs, the relations among charge transfer, metallization, and superconductivity were analyzed. The results indicate that the electronegativity of the metal element rather than the atomic radius is predominant in the charge transfer and superconductivity of metal-doped phenanthrene. [ABSTRACT FROM AUTHOR]

As one of the simplest hydrocarbons, methane (CH4) has great potential in the research of superconductors. However, the metallization of CH4 has been an issue for a long time. Here, we report the structure, metallization, and superconductivity of CH4 doped by Be at low pressures, based on first-principles calculations. The result shows that the thermodynamically stable BeCH4 with P1¯ space-group can transform into a metal at ambient pressure. This ternary hydride BeCH4 exhibits a superconductivity of ∼6 K below 25.6 GPa. Interestingly, the superconducting critical temperature of BeCH4 can reach ∼30 K at 80 GPa in the form of an a-P1 space-group phase. The charge transfer from Be to CH4 molecules plays an important role in the superconductivity. Our results present a novel way to realize the metallization of methane at relative pressures and indicate that the doped methane is a potential candidate for seeking high temperature and low pressure superconductivity. [ABSTRACT FROM AUTHOR]

Hydrogen‐rich materials are potential high‐temperature superconductors at pressures lower than metal hydrogen, mainly because hydrogen atoms can provide strong electron–phonon coupling and high phonon frequencies in hydrogen‐rich materials. This review provides a systematic overview of the crystal type, stability, pressure‐induced transition, metallization and superconductivity of binary light‐metal hydrides under high pressure. [ABSTRACT FROM AUTHOR]

Metallization of methane (CH4) has always been an interesting issue. Here, we report a study on the structure, metallization and superconductivity in K-doped CH4 under pressure, based on the particle swarm optimization, density functional theory, and density functional perturbation theory. Summarizing the thermodynamical and dynamical stabilities, the electronic band structures, and the electron–phonon interaction calculations, we predicted that K-doped CH4 in P 2 1 ∕ m space-group is a metal and a possible superconductor in the pressure range of 7 0 − 9 0 GPa. The superconducting critical temperature is about 12.7 K at 80 GPa. It was found that the charge transfer from K to CH4 drives the metallization and mainly contributes to the electron–phonon interaction. The result confirms that CH4 can become a metal and superconductor under the electron doping and the relative low pressure. [ABSTRACT FROM AUTHOR]

Phenyl molecules are proposed as potential high-temperature superconductors due to exhibiting interesting properties. Here, we report the discovery of superconductivity with the critical temperature (Tc) of ∼7.2 Kelvin in potassium (K)-doped biphenyl (C12H10). The dc magnetic susceptibility measurements provide solid evidence for the presence of the Meissner effect in KxC12H10. The Raman spectra detected bipolaronic characteristics in this superconducting state, which are proposed to account for the electron pairing. Theoretical simulations provided the information of the crystal structure of KxC12H10. Combining XRD data with formation energy, we suggest that the superconducting phase corresponds to K2C12H10 or with a small charge fluctuation in a layered structure. The discovery of superconductivity in K-doped biphenyl vastly expands the potential applications in the superconducting field. [ABSTRACT FROM AUTHOR]

Recently, an interesting superconductivity of the transition temperatures range from 7.2 to 43 K and then to 123 K in K-doped ${p}$ -terphenyl was reported, which attracts much attention. In this paper, to identify the superconducting phase from chemical component, we have investigated the crystal structures and electronic and magnetic properties in the cases of K-doped biphenyl and ${p}$ -terphenyl based on the first-principles calculations. We found that the change of doping concentration results in a series of magnetic transitions. Pristine biphenyl and ${p}$ -terphenyl are both nonmagnetic (NM) semiconductors. Doping one K atom for each organic molecule, the system exhibits the antiferromagnetism. With increasing the doping concentration of K atoms, however, the spin ordering disappears and the compound behaviors as the NM metal. Thus, we suggest that the superconducting phases observed experimentally are corresponding to the highly doping levels, which will deepen the understanding of the superconductivity of aromatic hydrocarbons. [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: Rice sheath blight is a globally important rice disease. Unfortunately, this critical disease has not been effectively controlled, and the intensive and continuous use of the same fungicide might increase the risk of resistance development in the pathogen. To discover new active agents against rice sheath blight, in this study, three series of β‐carboline urea, benzoylurea and benzoylthiourea derivatives were designed, synthesized and evaluated for in vitro and in vivo fungicidal activity against Rhizoctonia solani. RESULTS: All these compounds (EC50: 0.131–1.227 mmol L−1) exhibited better fungicidal activity than harmine itself (EC50: 2.453 mmol L−1). Significantly, compound 17c (EC50: 0.131 mmol L−1) displayed the best efficacy in vitro and superior fungicidal activity compared with validamycin A (EC50: 0.397 mmol L−1). Moreover, the in vivo bioassay also indicated that compound 17c could be effective for the control of rice sheath blight. CONCLUSION: Based on the bioassay result and quantitative structure–activity relationship (QSAR) information, structure modification in β‐carboline warrants further investigation and its benzoylurea derivative 17c, which showed the best fungicidal activities, could emerge as a potential fungicide against rice sheath blight. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons doped by metal have exhibited the potential of high temperature superconductivity. Understanding the basic properties of materials is the key to reveal the superconductivity. Here, a systemically theoretical study has been done to explore crystal structures and electronic properties of pristine and potassium-doped 1,2;8,9-dibenzopentacene, compared with [7]phenacenes case. We determined that vdW-DF2 functional is more suitable to describe the non-local interaction in a molecular crystal. Based on this functional, we predicted the crystal structures and investigated in detail the K atomic positions in a system. It was found that the intralayer doping leads to lower total energy. From the calculated formation energy, for each 1,2;8,9-dibenzopentacene molecule, the doping of two electrons is more stable under the relatively K-poor condition while the doping of four electrons is more stable under the K-rich condition. Between these two phases, the three-electron doping phase stabilises in a narrow region of K chemical potential. Combining with the electronic states at Fermi level, we analysed the reasons of superconductivity enhancement in doped 1,2;8,9-dibenzopentacene. This work further deepens the understanding of 1,2;8,9-dibenzopentacene superconductor. [ABSTRACT FROM PUBLISHER]

Based on the density functional theory, a theoretical determination method is applied to investigate structural and electronic properties of anthracene up to 27 GPa. The lattice parametersa, b, c, decrease by 1.53(−18.2%), 0.76(−12.8%), and 0.93(−8.4%), respectively, while the monoclinic angle β increased by 4.65° in this pressure region. At the highest pressure of 27 GPa the unit cell volume is decreased by 58.9%. These findings are shown to be in agreement with experimental results and hint towards the evolution of intermolecular interaction with pressure. The calculated electronic band splitting and the band gap reduce smoothly to some extent with the pressure increasing. Moreover, a pressure-induced decrease of the band gap is observed. [ABSTRACT FROM PUBLISHER]

Abstract: Single crystals of Y7Co6Sn23 and RE5Co6Sn18 (RE=Sc, Ho) have been obtained by solid-state reactions of the corresponding pure elements in welded tantalum tubes at high temperature. Their crystal structures have been established by single-crystal X-ray diffraction studies. Y7Co6Sn23 belongs to the Ho7Co6Sn23 type and crystallizes in the trigonal space group P-3m1 (No. 164) whereas RE5Co6Sn18 (RE=Sc, Ho) adopt the Tb5Rh6Sn18 type structure and crystallizes in the tetragonal space group I41/acd (No. 142). Their structures all feature a three-dimensional (3D) anionic framework based on [CoSn6] trigonal prisms. The structure of Y7Co6Sn23 is made from the ordinal stacking one type of 2D slab composed of the same [CoSn6] trigonal prisms via corner-sharing, forming two types of narrow tunnels along the c-axis, which are occupied by Y or residual Sn atoms. The 3D structure of RE5Co6Sn18 is built up from alternately stacking two types of 2D slabs, which are composed of different [CoSn6] trigonal prisms via corner-sharing and Sn–Sn bonds, respectively. The RE and residual Sn atoms are located in the spacers of the 3D framework. Band structure calculations indicate that Y7Co6Sn23 and Sc5Co6Sn18 are metallic. [Copyright &y& Elsevier]

Abstract: Two new ternary ytterbium transition metal stannides, namely, Yb3CoSn6 and Yb4Mn2Sn5, have been obtained by solid-state reactions of the corresponding pure elements in welded tantalum tubes at high temperature. Their crystal structures have been established by single-crystal X-ray diffraction studies. Yb3CoSn6 crystallizes in the orthorhombic space group Cmcm (no. 63) with cell parameters of a=4.662(2), b=15.964(6), c=13.140(5)Å, V=978.0(6)Å3, and Z=4. Its structure features a three-dimensional (3D) open-framework composed of unusual [CoSn3] layers interconnected by zigzag Sn chains, forming large tunnels along the c-axis which are occupied by the ytterbium cations. Yb4Mn2Sn5 is monoclinic space group C2/m (no. 12) with cell parameters of a=16.937(2), b=4.5949(3), c=7.6489(7)Å, β=106.176(4)°, V=571.70(8)Å3, and Z=2. It belongs to the Mg5Si6 structure type and its anionic substructure is composed of parallel [Mn2Sn2] ladders interconnected by unusual zigzag [Sn3] chains, forming large tunnels along the c-axis, which are filled by the ytterbium cations. Band structure calculations based on density function theory methods were also made for both compounds. [Copyright &y& Elsevier]

First-principles calculations are performed to investigate the magnetic characteristics in the tripotassium doped picene, especially for the effects induced by the volume variations. When changing volume, both crystal lattice constants and atomic positions are optimized. For the system with the experimental crystal volume, the doped picene shows a weak antiferromagnetic instability. When the volume expands from this experimental crystal volume, the antiferromagnetic spin ordering becomes clear. The electronic structures show that the magnetism comes from the spin unbalance on the π orbitals of the C atoms. On the contrary, both ferromagnetic and antiferromagnetic spin orderings are strongly suppressed as the volume is reduced. Our results indicate that the magnetism is sensitive to the variation of volume or pressure in the tripotassium doped picene. No metal-insulator transition is observed for several considered volumes. [ABSTRACT FROM AUTHOR]

The vibrational and structural properties of a hydrogen-rich group IVa hydride, Sn(CH3)4, have been investigated by combining Raman spectroscopy and synchrotron x-ray diffraction measurements at room temperature and at pressures up to 49.9 GPa. Both techniques allow the obtaining of complementary information on the high-pressure behaviors and yield consistent phase transitions at 0.9 GPa for the liquid to solid and 2.8, 10.4, 20.4, and 32.6 GPa for the solid to solid. The foregoing solid phases are identified to have the orthorhombic, tetragonal, monoclinic crystal structures with space groups of Pmmm for phase I, P4/mmm for phase II, P2/m for phase III, respectively. The phases IV and V coexist with phase III, resulting in complex analysis on the possible structures. These transitions suggest the variation in the inter- and intra-molecular bonding of this compound. [ABSTRACT FROM AUTHOR]