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An inorganic perovskite CsPbI3 with a suitable bandgap and excellent optoelectronic properties has attracted tremendous attention as a promising absorber in perovskite solar cells (PSCs). A surface modification strategy of introducing organic molecules with functional groups to treat perovskite films has been proven to be an effective route to achieve high-performance PSC devices. However, the effect of the molecular size of modifiers is almost ignored in surface passivation studies. In this work, three alkylamine modifiers with different molecular sizes were incorporated to post-treat CsPbI3 films to systematically investigate the influence of alkyl chain length on device performance. It was found that the alkylamine treatments can remarkably ameliorate film morphology and interface contact, passivate defects, and increase hydrophobicity, resulting in greatly improved device efficiency and stability. In particular, the CsPbI3 film treated with 1,5-pentanediamine (PDA) with a suitable chain length acquires optimum results owing to its most efficient passivation effect and suppressed nonradiative recombination. Consequently, the inverted PDA-based CsPbI3 PSC exhibits a champion power conversion efficiency (PCE) of 19.52%, outperforming the control device with a PCE of 13.43% and other alkylamine-treated devices. Furthermore, both the unencapsulated PDA-treated CsPbI3 films and PSC devices present considerably enhanced long-term stability. This work highlights the great significance of tailoring the molecular size of interfacial modifiers towards achieving efficient and stable inorganic PSCs. [ABSTRACT FROM AUTHOR]

As one promising member of the van der Waals layered materials, the metal phosphorus trichalcogenide (MPX3) family has attracted much attention on account of their unique and abundant properties, providing an excellent platform to further investigate exotic quantum states in low-dimensional systems. Here, we present a report on pressure-induced superconductivity in SnPSe3. The high-pressure studies combined with electrical transport, synchrotron X-ray diffraction, and Raman spectroscopy consistently reveal that a superconductivity transition emerges with metallization at a critical pressure Pc1 ∼ 16.2 GPa, which stems from the structural phase transition. Furthermore, SnPSe3 evolves into the amorphous state above Pc2 ∼ 31.9 GPa, while the superconductivity is suppressed, but still persists up to 80.2 GPa. These findings not only enrich the study of van der Waals materials, but also encourage us to explore novel superconductors by means of pressure treatment. [ABSTRACT FROM AUTHOR]

The recent discovery of high-temperature superconductivity in compressed hydrides has reignited the long-standing quest for room-temperature superconductors. However, the synthesis of superconducting hydrides under moderate pressure and the identification of crucial factors that affect their stability remain challenges. Here, we predicted the ternary clathrate phases of LaThH12 with potential superconductivity under high pressures and specifically proposed a novel R3¯c-LaThH12 phase exhibiting a remarkable Tc of 54.95 K at only 30 GPa to address these confusions. Our first-principles studies show that the high-Tc value of Pm3¯m and Cmmm-LaThH12 phases was induced by the strong electron–phonon coupling driven by the synergy of the electron–phonon matrix element and phonon softening caused by Fermi surface nesting. Importantly, we demonstrate the dual effects of enhanced ionic bonding and expanded orbital hybridization between Th-6f and H-sp3 orbitals during depressurization are primary factors governing the dynamic stability of R3¯c-LaThH12 at low pressures. Our findings offer crucial insights into the underlying mechanisms governing low-pressure stability and provide guidance for experimental efforts aimed at realizing hydrogen-based superconductors with both low synthesis pressures and high-Tc. [ABSTRACT FROM AUTHOR]

The experimentally discovered FeH5 exhibits a structure built of atomic hydrogen that only has bonding between hydrogen and iron atoms [C. M. Pepin, G. Geneste, A. Dewaele, M. Mezouar and P. Loubeyre, Science, 2017, 357, 382]. However, its superconductivity has remained unsolved since its discovery. In this work, we have synthesized I4/mmm-FeH5 at 139 GPa combined with laser-heating conditions. The electrical resistance measurements at ultrahigh pressures indicate that no evidence of superconducting transition of FeH5 is observed in the temperature range of 1.5 K to 270 K. These results indicate that I4/mmm-FeH5 does not exhibit superconductivity within the experimental temperature range, and the introduction of iron atoms is not beneficial to the formation of the superconducting phase. [ABSTRACT FROM AUTHOR]

High lattice thermal conductivity stemming from the intrinsically ordered crystal and strong interatomic bonds tends to be seen as the bottleneck for achieving excellent thermoelectric properties in full-Heusler (FH) semiconductors. In this work, we propose a novel Li-based FH compound Li2TlSb by substituting one Li atom with a Tl atom in Li3Sb. Then we systematically investigated its transport and thermoelectric properties based on self-consistent phonon (SCP) theory, electron–phonon scattering, and the Boltzmann transport equation. The theoretical calculation confirms that it exhibits outstanding mechanical properties and extreme environment adaptability. Surprisingly, the combination of an unexpectedly high spatial degeneracy and light electron dispersion at valence bands results in a high power factor in p-type systems. Additionally, the rattling behavior governed by the Tl atom and resonant bonding is responsible for ultra-low lattice thermal conductivity with 0.79 W m−1 K−1 at room temperature. Finally, a maximum p-type ZT value of 1.77 at 300 K has been achieved, which surpasses those of most of the traditional thermoelectric (TE) materials. Our results demonstrate that Li2TlSb serves as a potential candidate for room-temperature thermoelectric materials and simultaneously provides new insights for rationally designing novel FH materials in the future. [ABSTRACT FROM AUTHOR]

The search for high-temperature superconductors in hydrides under high pressure has always been a research hotspot. Hydrogen-based superconductors offer an avenue to achieve the long-sought goal of superconductivity at room temperature. Here we systematically explored the high-pressure phase diagram, electronic properties, lattice dynamics and superconductivity of the ternary Ca–Al–H system using ab initio methods. At 80 GPa, CaAlH5 transforms from Cmcm to P21/m phase. Both of Cmcm-CaAlH5 and Pnnm-CaAl2H8 are semiconductors. At 200 GPa, P4/mmm-CaAlH7 and a metastable compound Immm-Ca2AlH12 were found. Furthermore, P4/mmm-CaAlH7 shows obvious softening of the high frequency vibration modes, which improves the strength of electron–phonon coupling. Therefore, a superconducting transition temperature Tc of 71 K is generated in P4/mmm-CaAlH7 at 50 GPa. In addition, the thermodynamic metastable Immm-Ca2AlH12 exhibits a superconducting transition temperature of 118 K at 250 GPa. These results are very useful for the experimental searching of new high-Tc superconductors in ternary hydrides. Our work may provide an opportunity to search for high Tc superconductors at lower pressure. [ABSTRACT FROM AUTHOR]

Compressed hydrogen-rich compounds have received extensive attention as appealing contenders for superconductors. Here, we found several stable hydrides YZrH6, YZrH8, YZr3H16 and YZrH18, and a series of metastable clathrate hexahydrides in the systematic investigation of Y–Zr–H ternary hydrides under pressure. Electron-phonon coupling calculations indicate that they all exhibit high temperature superconductivity and perform better than the binary Zr–H system. YZrH6 can maintain dynamic stability down to ambient pressure and keep a critical temperature (Tc) of 16 K. The stable YZrH18 and metastable Y3ZrH24 with high hydrogen content exhibit high Tc of 156 K and 185 K at 200 GPa, respectively. Further analysis shows that the phonon modes associated with H atoms contribute significantly to the electron–phonon coupling. The hydrogen content and the stoichiometric ratio of Y and Zr closely affect the density of states at the Fermi level, thereby affecting the superconductivity. Our work presents an important step toward understanding the superconductivity and stability of transition metal ternary hydrides. [ABSTRACT FROM AUTHOR]

Due to the requirements of sustainable development and the widening application range, it is very necessary to develop lead-free eco-friendly piezoelectric materials with ultra-high Curie temperatures (Tc). The perovskite-like layered structure (PLS) Ca2Nb2O7 is considered a potential candidate with ultra-high Tc (1773 K). Herein, we prepared Ca2Nb2O7 single-crystals by the optical floating zone (OFZ) method. The piezoelectric constant d33 of Ca2Nb2O7 along the b-axis reaches 10.4 pC N−1 at room temperature and the d33 is enhanced to 15.2 pC N−1 when the temperature increases from 273 to 750 K. Furthermore, the origin of piezoelectricity as well as the mechanism of the orientation-dependent and thermally enhanced d33 of Ca2Nb2O7 were clarified based on the microstructure, lattice structure, and vibration by completely characterizing the corresponding parameters. [ABSTRACT FROM AUTHOR]

KSiH3 exhibits 4.1 wt% experimental hydrogen storage capacity and shows reversibility under moderate conditions, which provides fresh impetus to the search for other complex hydrides in the K–Si–H system. Here, we reproduce the stable Fm3¯m phase of K2SiH6 and uncover two denser phases, space groups P3¯m1 and P63mc at ambient pressure, by means of first-principles structure searches. We note that P3¯m1-K2SiH6 has a high hydrogen content of 5.4 wt% and a volumetric density of 88.3 g L−1. Further calculations suggest a favorable dehydrogenation temperature Tdes of −20.1/55.8 °C with decomposition into KSi + K + H2. The higher hydrogen density and appropriate dehydrogenation temperature indicate that K2SiH6 is a promising hydrogen storage material, and our results provide helpful and clear guidance for further experimental studies. We found three further potential hydrogen storage materials stable at high pressure: K2SiH8, KSiH7 and KSiH8. These results suggest the need for further investigations into hydrogen storage materials among such ternary hydrides at high pressure. [ABSTRACT FROM AUTHOR]

Titanium niobate (TiNb2O7) possesses excellent photocatalytic properties, dielectric properties, and lithium-insertion capacity. High-pressure (HP) treatment is a powerful tool for bandgap engineering aiming at widening its applications. Herein, we report the growth of TiNb2O7 single crystals by the optical floating zone (OFZ) method and the engineering of the TiNb2O7 bandgap via HP. To obtain the physical mechanism of the bandgap variation under HP, the detailed pressure-dependent properties and structure information have been characterized by using in situ Raman spectroscopy and angle dispersive synchrotron radiation X-ray diffraction (ADXRD). During compression, the TiNb2O7 crystals were amorphized and the amorphized phase was maintained under ambient conditions. The microstructures of the uncompressed crystalline and decompressed amorphized samples have also been investigated accordingly. [ABSTRACT FROM AUTHOR]

Conjugated porous polymers were successfully synthesized through dynamic covalent condensation polymerization using aromatic anhydrides and triacylhydrazine benzene. The obtained conjugated polymers with unique chemical stability, high specific surface area and electrochemically active carbonyl functional groups exhibited excellent performance as cathode materials for lithium-ion batteries. [ABSTRACT FROM AUTHOR]

The discovery of the high-temperature superconducting state in the compounds of hydrogen, carbon and sulfur with a critical temperature (Tc) of 288 K at high pressure is an important milestone towards room-temperature superconductors. Here, we have extensively investigated the high-pressure phases of CS2H10, and found four phases Cmc21, P3m1, P3¯m1 and Pm. Among them, P3m1 can be dynamically stable at a pressure as low as 50 GPa, and Cmc21 has a high Tc of 155 K at 150 GPa. Both Cmc21 and P3m1 are host–guest hydrides, in which CH4 molecules are inserted into Im3¯m-H3S and R3m-H3S sublattices, respectively. Their Tc is dominated by the H3S lattice inside. The insertion of CH4 molecules greatly reduces the pressure required for the stability of the original H3S lattice, but it has a negative impact on superconductivity which cannot be ignored. By studying the effect of CH4 insertion in the H3S lattice, we can design hydrides with a Tc close to that of H3S and a greatly reduced pressure required for stability. [ABSTRACT FROM AUTHOR]

Hydrogen passivation is an important method used to stabilize a specific graphene edge. Although several hydrogen-terminated graphene edges have been proposed in theory, a comprehensive exploration of highly stable hydrogen-terminated graphene edges is still absent. According to the bare graphene-edge databases, a series of hydrogen-terminated graphene edges have been proposed. The energy stability of hydrogen-terminated zigzag and armchair graphene edges is fully investigated. The six most stable hydrogen-terminated zigzag edges and six armchair edges of graphene are determined. Hydrogen passivation makes hydrogen-terminated graphene edges energetically more stable than bare graphene edges. The additional hydrogen atoms balance the dangling bonds of carbon atoms at edges by forming hydrogen–carbon covalent bonds. Hydrogen-terminated graphene edges with six-membered carbon rings have better global stability than those composed of non-hexagonal structural units. The effects of the experimental temperatures and hydrogen partial pressures on the stability of hydrogen-terminated graphene edges are fully investigated. Furthermore, hydrogen passivation can open the band gap of graphene effectively. These results provide a deep understanding of hydrogen-terminated graphene nanostructures. [ABSTRACT FROM AUTHOR]

Pressure has been considered as an effective technique to modulate the structural, electronic, and optical properties of transition metal dichalcogenide (TMDs) materials. Here, by performing in situ high pressure Raman, photoluminescence (PL) and absorption measurements, we systematically investigated the vibrational and electronic properties evolution of monolayer MoSe2 grown on a SiO2/Si substrate under high pressure. When the pressure increased up to 4.84 GPa, an unexpected phonon mode at 367 cm−1 appeared, which was identified as the Raman-inactive A2′′ mode and was activated under high pressure. Combined with the analysis of absorption spectroscopy, this phenomenon can be attributed to the pressure-induced wrinkle and near-resonance effects in compressed monolayer MoSe2. Subsequently, A1′ split into two peaks after 7.44 GPa, providing further distinct evidence for the pressure-induced wrinkle effect in compressed monolayer MoSe2. Moreover, this wrinkle effect can also lead to a rapid quenching of photoluminescence in monolayer MoSe2. These results suggest that the substrate plays an important role in determining the vibrational and electronic properties of compressed monolayer MoSe2, and can provide valuable information on the electronic and optoelectronic applications of monolayer MoSe2 under extreme conditions. [ABSTRACT FROM AUTHOR]

The discovery of H3S and LaH10 is an important step towards the development of room temperature superconductors which fuels the enthusiasm for finding promising superconductors among hydrides at high pressure. In the present study, three new and stable stoichiometric MoH5, MoH6 and MoH11 compounds were found in the pressure range of 100–300 GPa. The highly hydrogen-rich phase of Cmmm-MoH11 has a layered structure that contains various forms of hydrogen: H, H2− and H3− units. It is a high-Tc material with an estimated Tc value in the range of 165–182 K at 250 GPa. The same structures are also found in NbH11, TaH11, and WH11, each material showing Tc ranging from 117 to 168 K. By combining the method of using two coupling constants λopt and λac, and two characteristic frequencies (optical and acoustic) with first-principle calculations, we found that the high values of Tc are mainly caused by the presence of high frequency optical modes, but the acoustic modes also play a noticeable role. [ABSTRACT FROM AUTHOR]

Magnetic materials attract great attention due to their fundamental importance and practical application. However, the relatively inferior mechanical properties of traditional magnetic materials limit their application in a harsh environment. In this work, we report an outstanding magnetic material that exhibits both fantastic mechanical and excellent magnetic properties, CuAl2-type Fe2B, synthesized by the high pressure and high temperature method. The magnetic saturation of Fe2B is 156.9 emu g−1 at room temperature and its Vickers hardness is 12.4 GPa which outclasses those of traditional magnetic materials. It exhibits good conductivity with a resistivity of 5.6 × 10−7 Ω m. Fe2B is a promising strong ferromagnetic material with high hardness, which makes it a good candidate for multifunction applications in a harsh environment. The high hardness of Fe2B originates from the Fe–B bond framework, and the strong ferromagnetism is mainly attributed to the large number of unpaired Fe 3d electrons. The competition of Fe 3d electrons to fall into Fe–B bonds or Fe–Fe bonds is the main factor for its magnetism and hardness. This work bridges the chasm between strong ferromagnetism and high hardness communities. [ABSTRACT FROM AUTHOR]

High-pressure technology can help us to obtain excellent materials. We have explored alkaline-earth-metal strontium nitrides under different pressures, theoretically. A variety of stable Sr–N structures were predicted by the structure searching method using CALYPSO code. Six new stoichiometries, SrN, Sr2N3, SrN2, SrN3, SrN4, and SrN5, were predicted. And our calculation proved that all these compounds were stable existing under ambient pressure up to 100 GPa. A rich variety of poly-nitrogen forms appeared in the newly predicted SrNx compounds, including four nitrogen polymerization forms: ranging from N2, N3, N4, and N5 molecules, to zig-zag nitrogen chains and extended chains connected by puckered "N6" rings. Significantly, the 1D extended polymeric chain of puckered "N6" rings was firstly identified in the P1¯-SrN3 structure at 60 GPa. Another N-rich C2/c-SrN4 was stable only under the relatively high-pressure of 20 GPa, but this phase can be quenched under atmospheric pressure. The N-rich phase SrN5 maintained structural stability when the pressure reached 50–70 GPa. The delocalization of π electrons from N atoms was the principal cause for its metallicity in SrN5. In this paper, our calculated results indicated that the energetic poly-nitrides in alkaline-earth-metal nitrides can be obtained by the high-pressure method. [ABSTRACT FROM AUTHOR]

Harvesting clean energy from fuel feedstocks is of paramount significance in the field of environmental science. In this dynamic area, desulfurization provides a valuable contribution by eliminating sulfur compounds from fuel feedstocks to ensure the utilization of fuels without the emission of toxic sulfur oxides (SOx gases). Nonetheless, the inadequacy of the current industrial technique (hydrodesulfurization, HDS) in the removal of refractory sulfur (RS) compounds and the stringent rules imposed on the fuel sulfur level have kindled research on other desulfurization methods like oxidative desulfurization (ODS). With the capacity of eliminating RS compounds under mild conditions, ODS is endorsed as a suitable replacement or complementary to HDS. ODS, in general, consists of two steps: (i) oxidation and (ii) extraction. The oxidation of sulfur compounds is carried out using a suitable catalyst (hereafter termed as an ODS catalyst) in the presence of an oxidant. Choosing a suitable ODS catalyst for industrial applications is still a quest among the various types of catalysts reported so far. With this outline, herein, all the types of ODS catalysts along with their synthetic methods, reactivity and mechanistic insights are reviewed. The activity of ODS catalysts could be influenced by factors like the type of RS compound, solvent, fuel, etc. and those factors are reviewed. The effects of ionic liquids, light, and ultrasound on the performance of ODS catalysts are also briefly summarized. The opportunities and challenges for ODS catalysts are comprehensively explicated in the end. Through this review, systematic information about the types of ODS catalysts including the basic definition, preparative methods, reactivity and mechanism can be comprehended. Furthermore, this review reveals the merits and demerits related to highlighting catalytic ODS as a replacement or complementary to HDS. [ABSTRACT FROM AUTHOR]

Hydrogen chloride (HCl) is the simplest hydrogen-bonded molecule and has attracted a great deal of attention owing to its interesting structural changes triggered by pressure or temperature. The structural properties of solid HCl have been investigated by Brillouin scattering in the pressure range of 0–20 GPa under high temperature, combined with external heating in a diamond anvil cell. Three elastic constants and two moduli of the single crystal sample were observed at high pressure–temperature and each of them grows monotonously with pressure along a separate isotherm. The pressure dependence of elastic anisotropy proves that the disorder–order transition pressures are 4.5 GPa, 5.4 GPa and 8.8 GPa for the 300 K, 390 K and 470 K isotherms, respectively. The current work discovered the disorder–order structural transition in HCl and extended its phase diagram to the high pressure–temperature range, also providing a new insight into other simple hydrogen-bonded molecular compounds. [ABSTRACT FROM AUTHOR]

High pressure can stimulate numerous novel physical effects which are not observed under ambient conditions, such as the electronic redistribution and delocalization phenomenon in strongly covalently bonded nitrides. Through first principles simulations, we report a new N-rich aluminum nitride AlN5, which crystallizes with the space group P1̅ at 20 GPa and then transforms into the I4̅2d phase at 60 GPa. We have identified and proved the delocalization effects of π electrons in the strongly covalent Lewis poly-nitrogen structure via the one-dimensional particle in a box mechanism, which contributes to the metallization and stability of the system. This implies that not all strongly covalently bonded systems with highly localized electrons exhibit nonmetallic properties in III–V main group nitrides. Furthermore, pressure results in the hybridization configuration mutation from sp2 in the P1̅ phase to a mixture of sp2 and sp3 hybridization in the I4̅2d phase, which leads to phase transition from metal to insulator. With increasing pressure, the band gap increases abnormally, exhibiting anti-metallization induced by the strong hybridization. Interestingly, the P1̅ and I4̅2d structures are simultaneously accompanied by a high energy density and hardness, which enable them to have a greater ability to resist elasticity, plastic deformation and external force destruction in potential applications. Their energy density and hardness are up to 3.29 kJ g−1 and 15.2 GPa in the P1̅ phase but especially 6.14 kJ g−1 and 31.7 GPa in the I4̅2d phase. [ABSTRACT FROM AUTHOR]

The D7b-type structure Mn3B4 was fabricated by high-temperature and high-pressure (HPHT) methods. Hardness examination yielded an asymptotic Vickers hardness of 16.3 GPa, which is much higher than that of Mn2B and MnB2. First principle calculations and XPS results demonstrated that double zigzag boron chains form a strong covalent skeletons, which enhances this structure's integrity with high hardness. Considering that the hardensses of MnB and Mn3B4 are higher than those of Mn2B and MnB2, zigzag and double zigzag boron backbones are superior to isolated boron and graphite-like boron layer backbones for achieving higher hardness. This situation also states that a higher boron content is not the sole factor for the higher hardness in the low boron content transition metal borides. Futhermore, the co-presence of metallic manganese bilayers contribute to the high d-electron mobility and generate electrical conductivity and antiferromagnetism in Mn3B4 which provide us with a new structure prototype to design general-purpose high hardness materials. [ABSTRACT FROM AUTHOR]

This work presents the influence of chloride treatment on the photovoltaic performance, microstructure, charge carrier dynamics, and surface chemical composition of aqueous-processed CdTe nanocrystal (NC)-based hybrid solar cells (HSCs). By applying CdCl2 treatment on the CdTe films through a spin-coating method, the power conversion efficiency (PCE) of the HSCs is largely improved from 4.49% to 6.01%. We show that the main role of chloride treatment is to promote the grain growth of the CdTe NCs, which leads to an increase in charge carrier lifetime. It is also demonstrated that CdCl2 treatment can prevent the generation of detrimental surface oxides and improve the wettability of the CdTe films. [ABSTRACT FROM AUTHOR]

The phase diagram, electronic properties and superconductivity of an At–H system at high pressure are investigated through first principles calculation considering the effect of spin–orbit coupling (SOC). The Cmcm-AtH2, Pnma-AtH2, P6/mmm-AtH4, and Cmmm-AtH4 phases are uncovered above 50 GPa. Metallization is realized at 50 GPa for AtH2 and 60 GPa for AtH4, with Tc values of approximately 5–10 K and 30–50 K, respectively. In P6/mmm-AtH4, phonon softening induced by Fermi surface nesting occurs as the pressure increases, which is closely related to the structural phase transition of P6/mmm→Cmmm and plays a crucial role in the superconductivity of the P6/mmm phase. In addition, the spin–orbit coupling effect considerably influences the energy of ground states, pressure points of phase transitions, electronic structures, and even the electron–phonon coupling of the At–H system. Such an influence may also occur in other heavy atomic hydrides. [ABSTRACT FROM AUTHOR]

A novel base-mediated direct difluoroalkylation of 1,6-enynes involving a CF2 radical process has been developed. In the absence of metal catalysts, two different difluoroalkylated cyclization products have been synthesized with good functional group applicability and high stereoselectivity. Notably, the properties of a base have been shown to play a crucial role in the generation selectivity of this transformation. [ABSTRACT FROM AUTHOR]

Pressure-induced molecular dissociation provides significant insights into chemical bonding, governing the physical properties of molecular solids. Here the typical molecular solids, selenium and tellurium, have been explored experimentally to unearth the process of pressure-induced molecular dissociation. Before molecular dissociation, both commensurately and incommensurately modulated structures have been observed in these two elements. Upon compression, the successive commensurate–incommensurate phase transitions are proved by the soft amplitude (AMP) mode. The fitted critical pressure suggests that the molecular dissociation of Te is inferred to occur at 26.1 GPa in agreement with our XRD and Raman data. The current precise structural studies before pressure-induced molecular dissociation demonstrated in the elements selenium and tellurium will help in clarifying the mechanisms of molecular dissociation in related molecular solids. [ABSTRACT FROM AUTHOR]

Hard materials are being investigated all the time by combining transition metals with light elements. Combining a structure search with first-principles functional calculations, we first discovered three stable stoichiometric C-rich ruthenium carbides in view of three synthesis routes, namely, the ambient phases of Ru2C3 and RuC, and two high pressure phases of RuC4. There is a phase transition of RuC4 from the P3̅m1 structure to the R3̅m structure above 98 GPa. The calculations of elastic constants and phonon dispersions show their mechanical and dynamical stability. The large elastic modulus, high Debye temperature and the estimated hardness values suggest that these hard ruthenium carbides have good mechanical properties. The analyses of electronic structure and chemical bonding indicate that chemical bonding, not carbon content, is the key factor for the hardness in these metallic C-rich ruthenium carbides. The partial covalent Ru–C bonds and strong covalent C–C bonds are responsible for the high hardness. Moreover, the emergence of partial covalent Ru–Ru bonds can enhance the hardness of RuC, while the ionic Ru–Ru bonds can weaken the hardness of Ru2C3. [ABSTRACT FROM AUTHOR]

This communication reports on a fluorescent probe (PPI-P) for imaging active peptidyl-prolyl cis/trans isomerases in live cells. PPI-P is capable of responding to both recombinant and cellular PPIases fluorogenically, and has been shown to specifically image active PPIases in live cells. [ABSTRACT FROM AUTHOR]

Invigorated by the high temperature superconductivity in some binary hydrogen-dominated compounds, we systematically explored high-pressure phase diagrams and superconductivity of a ternary Mg–Ge–H system using ab initio methods. Stoichiometric MgGeH6 with high hydrogen content exhibiting Pm3̅ symmetry was predicted from a series of high-pressure synthesis paths. We performed an in-depth study on three distinct formation routes to MgGeH6, i.e., Mg + Ge + 3H2→ MgGeH6, MgGe + 3H2→ MgGeH6 and MgH2 + GeH4→ MgGeH6 at high pressures. By directly squeezing three elemental solids Mg + Ge + 3H2, we obtained ternary MgGeH6 at 200 GPa. By adding a little bit of the MgGe alloy into hydrogen, we found that MgGeH6 can form and stabilize at about 200 GPa. More intriguingly, upon compressing MgH2 and GeH4 to 250 GPa, we also predicted the same MgGeH6. Electron structure calculations reveal that the cubic MgGeH6 is a good metal and takes on ionic character. Electron–phonon coupling calculation reveals a large λ = 1.16 for MgGeH6 at 200 GPa. In particular, we found that ternary MgGeH6 could be a potential high temperature superconductor with a superconducting transition temperature Tc of ∼67 K at 200 GPa. [ABSTRACT FROM AUTHOR]

Aiming at finding new superconducting materials, we performed systematical simulations on phase diagrams, crystal structures, and electronic properties of vanadium hydrides under high pressures. The VH, VH2, VH3, and VH5 species were found to be stable under high pressures; among these, VH2 had previously been investigated. Moreover, all three novel stoichiometries showed a strong ionic character as a result of the charge transfer from V to H. The electron–phonon coupling calculations revealed the potentially superconductive nature of these vanadium hydrides, with estimated superconducting critical temperature (Tc) values of 6.5–10.7 K for R3M̄m (VH), 8.0–1.6 K for Fm3M̄m (VH3), and 30.6–22.2 K for P6/mmm (VH5) within the pressure range from 150 GPa to 250 GPa. [ABSTRACT FROM AUTHOR]

The high-pressure structural evolutionary behaviors of magnesium polynitrides were studied up to 100 GPa using first-principles calculations. Using the unbiased structure searching method, five stable chemical stoichiometries of magnesium polynitrides (MgN, Mg2N3, MgN2, MgN3, and MgN4) were theoretically predicted at high pressures. The predicted MgNx compounds contain a rich variety of polynitrogen forms ranging from charged molecules (one-dimensional bent molecules N3, planar triangle N4 to benzene-like rings N6) to extended polymeric chains (N∞). To the best of our knowledge, this is the first time that stable bent molecules N3, planar triangle N4, and polymeric chains (N∞) were predicted in alkaline-earth metal polynitrides. The decomposition of P1̅-MgN3 and P1̅-MgN4 are expected to be highly exothermic, releasing an energy of approximately 2.83 kJ g−1 and 2.01 kJ g−1, respectively. Furthermore, P1̅-MgN4 can be synthesized at several GPa. The results of the present study suggest that it is possible to obtain energetic polynitrogen in main-group nitrides under high pressure. [ABSTRACT FROM AUTHOR]

In this work, the structure of WB2 synthesized at high pressure and high temperature (HPHT) was accurately determined by X-ray diffraction and Rietveld refinement. Its asymptotic Vickers hardness (Hv) value is 25.5 GPa which is much lower than the previous theoretical results (36–40 GPa). It is worth noting that the chemical bonds between the W layers and two different kinds of B layers show obvious polarization character based on the results obtained from X-ray photoelectron spectroscopy (XPS) and electron localization functions (ELFs), density of states (DOS), topological analysis of the static electron density and Mulliken population. This result can well clarify that WB2 is only a hard but not superhard material. Thus, a 3D network structure can not be formed between the W layers and the B layers which is previously predicted by theoretical calculations. Our results are helpful to understand the hardness mechanism and design superhard materials in TMBs. [ABSTRACT FROM AUTHOR]