Structural Phase Transition and Decomposition of XeF2 under High Pressure and Its Formation of Xe-Xe Covalent Bonds.

Noble gases with inert chemical properties have rich bonding modes under high pressure. Interestingly, Xe and Xe form covalent bonds, originating from the theoretical simulation of the pressure-induced decomposition of XeF2, which has yet to be experimentally confirmed. Moreover, the structural phase transition and metallization of XeF2 under high pressure have always been controversial. Therefore, we conducted extensive experiments using a laser-heated diamond anvil cell technique to investigate the above issues of XeF2. We propose that XeF2 undergoes a structural phase transition and decomposition above 84.1 GPa after laser heating, and the decomposed product Xe2F contains Xe-Xe covalent bonds. Neither the pressure nor temperature alone could bring about these changes in XeF2. With our UV-vis absorption experiment, I4/mmm-XeF2 was metalized at 159 GPa. This work confirms the existence of Xe-Xe covalent bonds and provides insights into the controversy surrounding XeF2, enriching the research on noble gas chemistry under high pressure.

Structural phase transition and potential superconductivity initiated by pressure-driven in 1T-CrSe2.

The exploration of the superconducting properties of antiferromagnetic parent compounds containing transition metals under pressure provides a unique idea for finding and designing superconducting materials with better performance. In this paper, the close relationship between the possible superconductivity and structure phase transition of the typical van der Waals layered material 1T-CrSe2 induced by pressure is studied by means of electrical transport and X-ray diffraction for the first time. We introduce the possibility of pressure-induced superconductivity at 20 GPa, with a critical Tc of approximately at 4 K. The superconductivity persists up to the highest measured pressure of 70 GPa, with a maximum Tc ~ 5 K at 24 GPa. We observed a structure phase transition from P-3m1 to C2/m space group in the range of 9.4-11.7 GPa. The results show that the structural phase transition leads to the metallization of 1T-CrSe2, and the further pressure effect makes the superconductivity appear in the new structure. The material undergoes a transition from a two-dimensional layered structure to a three-dimensional structure under pressure. This is the first time that possible superconductivity has been observed in 1T-CrSe2.

Superconducting ternary hydrides: progress and challenges.

Since the discovery of the high-temperature superconductors H3S and LaH10 under high pressure, compressed hydrides have received extensive attention as promising candidates for room-temperature superconductors. As a result of current high-pressure theoretical and experimental studies, it is now known that almost all the binary hydrides with a high superconducting transition temperature (T c) require extremely high pressure to remain stable, hindering any practical application. In order to further lower the stable pressure and improve superconductivity, researchers have started exploring ternary hydrides and had many achievements in recent years. Here, we discuss recent progress in ternary hydrides, aiming to deepen the understanding of the key factors regulating the structural stability and superconductivity of ternary hydrides, such as structural motifs, bonding features, electronic structures, electron-phonon coupling, etc. Furthermore, the current issues and challenges of superconducting ternary hydrides are presented, together with the prospects and opportunities for future research.

Stabilization of High-Pressure Phase of Face-Centered Cubic Lutetium Trihydride at Ambient Conditions.

Superconductivity at room temperature and near-ambient pressures is a highly sought-after phenomenon in physics and materials science. A recent study reported the presence of this phenomenon in N-doped lutetium hydride [Nature 615, 244 (2023)], however, subsequent experimental and theoretical investigations have yielded inconsistent results. This study undertakes a systematic examination of synthesis methods involving high temperatures and pressures, leading to insights into the impact of the reaction path on the products and the construction of a phase diagram for lutetium hydrides. Notably, the high-pressure phase of face-centered cubic LuH3 (fcc-LuH3) is maintained to ambient conditions through a high-temperature and high-pressure method. Based on temperature and anharmonic effects corrections, the lattice dynamic calculations demonstrate the stability of fcc-LuH3 at ambient conditions. However, no superconductivity is observed above 2 K in resistance and magnetization measurements in fcc-LuH3 at ambient pressure. This work establishes a comprehensive synthesis approach for lutetium hydrides, thereby enhancing the understanding of the high-temperature and high-pressure method employed in hydrides with superconductivity deeply.

Strategies for improving the superconductivity of hydrides under high pressure.

The successful prediction and confirmation of unprecedentedly high-temperature superconductivity in compressed hydrogen-rich hydrides signify a remarkable advancement in the continuous quest for attaining room-temperature superconductivity. The recent studies have established a broad scope for developing binary and ternary hydrides and illustrated correlation between specific hydrogen motifs and high-Tcs under high pressures. The analysis of the microscopic mechanism of superconductivity in hydrides suggests that the high electronic density of states at the Fermi level (EF), the large phonon energy scale of the vibration modes and the resulting enhanced electron-phonon coupling are crucial contributors towards the high-Tcphonon-mediated superconductors. The aim of our efforts is to tackle forthcoming challenges associated with elevating theTcand reducing the stabilization pressures of hydrogen-based superconductors, and offer insights for the future discoveries of room-temperature superconductors. Our present Review offers an overview and analysis of the latest advancements in predicting and experimentally synthesizing various crystal structures, while also exploring strategies to enhance the superconductivity and reducing their stabilization pressures of hydrogen-rich hydrides.

Superconductivity of thulium substituted clathrate hexahydrides at moderate pressure.

Due to the BCS theory, hydrogen, the lightest element, would be the prospect of room-temperature superconductor after metallization, but because of the difficulty of the hydrogen metallization, the theory about hydrogen pre-compression was proposed that the hydrogen-rich compounds could be a great option for the high Tc superconductors. The superior properties of TmH6, YbH6 and LuH6 indicated the magnificent potential of heavy rare earth elements for low-pressure stability. Here, we designed XTmH12 (X = Y, Yb, Lu, and La) to obtain higher Tc while maintaining low pressure stability. Most prominently, YbTmH12 can stabilize at a pressure of 60 GPa. Compared with binary TmH6 hydride, its Tc was increased to 48 K. The results provide an effective method for the rational design of moderate pressure stabilized hydride superconductors.

Superior Superconducting Properties Realized in Quaternary La-Y-Ce Hydrides at Moderate Pressures.

The recent revolution in the superconductivity field stems from hydride superconductors. Multicomponent hydrides provide a crucial platform for tracking high-temperature superconductors. Besides high superconducting transition temperature (Tc), achieving both giant upper critical magnetic field [µ0Hc2(0)] and high critical current density [Jc(0)] is also key to the latent potential of the application for hydride superconductors. In this work, we have successfully synthesized quaternary La-Y-Ce hydrides with excellent properties under moderate pressure by using the concept of "entropy engineering." The obtained temperature dependence of the resistance provides evidence for the superconductivity of Fm3m-(La,Y,Ce)H10, with the maximum Tc ∼ 190 K (at 112 GPa). Notably, Fm3m-(La,Y,Ce)H10 boasts exceptional properties: µ0Hc2(0) reaching 292 T and Jc(0) surpassing 4.61 × 107 A/cm2. Compared with the binary LaH10/YH10, we find that the Fm3m structure in (La,Y,Ce)H10 can be stable at relatively low pressures (112 GPa). These results indicate that multicomponent hydrides can significantly enhance the superconducting properties and regulate stabilizing pressure through the application of "entropy engineering." This work stimulates the experimental exploration of multihydride superconductors and also provides a reference for the search of room-temperature superconductors in more diversified hydride materials in the future.

Ultralow Glassy Thermal Conductivity and Controllable, Promising Thermoelectric Properties in Crystalline o-CsCu5S3.

We thoroughly investigated the anharmonic lattice dynamics and microscopic mechanisms of the thermal and electronic transport characteristics in orthorhombic o-CsCu5S3 at the atomic level. Taking into account the phonon energy shifts and the wave-like tunneling phonon channel, we predict an ultralow κL of 0.42 w/mK at 300 K with an extremely weak temperature dependence following ∼T-0.33. These findings agree well with experimental values along with the parallel to the Bridgman growth direction. The κL in o-CsCu5S3 is suppressed down to the amorphous limit, primarily due to the unconventional Cu-S bonding induced by the p-d hybridization antibonding state coupled with the stochastic oscillation of Cs atoms. The nonstandard temperature dependence of κL can be traced back to the critical or dominant role of wave-like tunneling of phonon contributions in thermal transport. Moreover, the p-d hybridization of Cu(3)-S bonding results in the formation of a valence band with "pudding-mold" and high-degeneracy valleys, ensuring highly efficient electron transport characteristics. By properly adjusting the carrier concentration, excellent thermoelectric performance is achieved with a maximum thermoelectric conversion efficiency of 18.4% observed at 800 K in p-type o-CsCu5S3. Our work not only elucidates the anomalous electronic and thermal transport behavior in the copper-based chalcogenide o-CsCu5S3 but also provides insights for manipulating its thermal and electronic properties for potential thermoelectric applications.

One-Dimensional Non-coplanar Nitrogen Chains in Manganese Tetranitride under High Pressure.

Transition metal nitrides have great potential applications as incompressible and high energy density materials. Various polymeric nitrogen structures significantly affect their properties, contributing to their complex bonding modes and coordination conditions. Herein, we first report a new manganese polynitride MnN4 with bifacial trans-cis [N4]n chains by treating with high-pressure and high-temperature conditions in a diamond anvil cell. Our experiments reveal that MnN4 has a P-1 symmetry and could stabilize in the pressure range of 56-127 GPa. Detailed pressure-volume data and calculations of this phase indicate that MnN4 is a potential hard (255 GPa) and high energy density (2.97 kJ/g) material. The asymmetric interactions impel N1 and N4 atoms to hybridize to sp2-3, which causes distortions of [N4]n chains. This work discovers a new polynitride material, fills the gap for the study of manganese polynitride under high pressure, and offers some new insights into the formation of polymeric nitrogen structures.

First-principles study of high-pressure structural phase transition and superconductivity of YBeH8.

The theory-led prediction of LaBeH8, which has a high superconducting critical temperature (Tc) above liquid nitrogen under a pressure level below 1 Mbar, has been experimentally confirmed. YBeH8, which has a structural configuration similar to that of LaBeH8, has also been predicted to be a high-temperature superconductor at high pressure. In this study, we focus on the structural phase transition and superconductivity of YBeH8 under pressure by using first-principles calculations. Except for the known face-centered cubic phase of Fm3̄m, we found a monoclinic phase with P1̄ symmetry. Moreover, the P1̄ phase transforms to the Fm3̄m phase at ∼200 GPa with zero-point energy corrections. Interestingly, the P1̄ phase undergoes a complex electronic phase transition from semiconductor to metal and then to superconducting states with a low Tc of 40 K at 200 GPa. The Fm3̄m phase exhibits a high Tc of 201 K at 200 GPa, and its Tc does not change significantly with pressure. When we combine the method using two coupling constants, λopt and λac, with first-principles calculations, λopt is mainly supplied by the Be-H alloy backbone, which accounts for about 85% of total λ and makes the greatest contribution to the high Tc. These insights not only contribute to a deeper understanding of the superconducting behavior of this ternary hydride but may also guide the experimental synthesis of hydrogen-rich compounds.

Pressure-driven dome-shaped superconductivity in topological insulator GeBi2Te4.

The discovery of new superconductors based on topological insulators always captures special attention due to their unique structural and electronic properties. High pressure is an effective way to regulate the lattice as well as electronic states in the topological insulators, thus altering their electronic properties. Herein, we report the structural and electrical transport properties of the topological insulator GeBi2Te4by using high-pressure techniques. The synchrotron x-ray diffraction revealed that GeBi2Te4underwent two structural phase transitions fromR-3m(phase I) toC2/m(phase II) and then intoIm-3m(phase III). Superconductivity was observed at 6.6 GPa to be associated with the first structural phase transition. The superconducting transition temperatureTcreached a maximum value of 8.4 K, accompanied by theRHsign changing from negative to positive at 14.6 GPa, then gradually decreased with increasing pressure in phase III, showing a dome-shaped phase diagram. The present results provide a platform for understanding the interplay between the crystal structure and superconductivity by the regulation of pressure in the topological insulator materials.

Novel room-temperature full-Heusler thermoelectric material Li2TlSb.

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.

Absence of superconductivity in I4/mmm-FeH5: experimental evidence.

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.

High-temperature superconductivities and crucial factors influencing the stability of LaThH12 under moderate pressures.

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 R3̄c-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 Pm3̄m 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 R3̄c-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.

Strain-Tunable Hyperbolic Exciton Polaritons in Monolayer Black Arsenic with Two Exciton Resonances.

Hyperbolic polaritons have been attracting increasing interest for applications in optoelectronics, biosensing, and super-resolution imaging. Here, we report the in-plane hyperbolic exciton polaritons in monolayer black-arsenic (B-As), where hyperbolicity arises strikingly from two exciton resonant peaks. Remarkably, the presence of two resonances at different momenta makes overall hyperbolicity highly tunable by strain, as the two exciton peaks can be merged into the same frequency to double the strength of hyperbolicity as well as light absorption under a 1.5% biaxial strain. Moreover, the frequency of the merged hyperbolicity can be further tuned from 1.35 to 0.8 eV by an anisotropic biaxial strain. Furthermore, electromagnetic numerical simulation reveals a strain-induced hyperbolicity, as manifested in a topological transition of iso-frequency contour of exciton polaritons. The good tunability, large exciton binding energy, and strong light absorption exhibited in the hyperbolic monolayer B-As make it highly suitable for nanophotonics applications under ambient conditions.

Risk factors for hypotension in patients with hemodialysis-associated superior vena cava syndrome.

OBJECTIVE: We analyzed the risk factors for hypotension in patients with hemodialysis-associated superior vena cava syndrome (SVCS) and effectiveness of endovascular intervention in hypotension related to SVCS. METHODS: This was a retrospective cohort study. A total of 194 maintenance hemodialysis patients diagnosed with SVCS who were admitted to the Department of Nephrology, West China Hospital of Sichuan University from January 2019 to December 2021 were selected and divided into a hypotension group and a nonhypotension group. Demographic and clinical data were compared. Hypotension simply refers to blood pressure levels of <90/60 mm Hg on a nondialysis day. All patients received endovascular intervention. RESULTS: Hypotension was found in 85 of the 194 patients. The following factors were significantly different between the hypotension and nonhypotension groups: body mass index, history of hypertension, tunneled-cuffed catheter as the means of dialysis access, azygos ectasis, SVC stenosis of >70% or occlusion, occlusion at the cavitary junction, serum calcium, diastolic left ventricular (LV) posterior wall thickness, LV end-diastolic volume, stroke output, and LV ejection fraction. Multivariate logistic regression analysis showed that hypertension history (OR, 0.314; P = .027), tunneled-cuffed catheter as vascular access (OR, 3.997; P < .001), SVC stenosis of >70% or occlusion (OR, 5.243; P < .001), LV posterior wall thickness (OR, 0.772; P = .044), and serum calcium (OR, 0.146; P = .005) were independent risk factors for hypotension. The mean values of systolic and diastolic blood pressure after intravascular treatment were significantly elevated from those before intervention (P < .001). The primary patency rates of SVC were 66.8%, 58.7%, and 50.0% at 3, 6, and 12 months after the procedure. CONCLUSIONS: The incidence of hypotension in patients with hemodialysis-associated SVCS is high. The identification of risk factors of hemodialysis-related hypotension provides insight into potential treatment strategies. Endovascular treatment is expected to improve hypotension related to SVCS in hemodialysis patients.

Fingerprinting and characterization of the polysaccharides from Polygonatum odoratum and the in vitro fermented effects on Lactobacillus johnsonii.

Polygonatum odoratum (Yu-Zhu) can be utilized to treat the digestive and respiratory illness. Previous studies have revealed that the underlying therapeutic mechanism of P. odoratum polysaccharides (POPs) is associated with remodeling the gut microbiota. However, POPs in terms of the chemical composition and fermentation activities have been understudied. Here we developed the three-level fingerprinting approaches to characterize the structures of POPs and probed into the beneficial effects on promoting the growth and fermentation of Lactobacillus johnsonii. POPs were prepared by water decoction followed by alcohol sedimentation, while trifluoroacetic acid under different conditions to prepare the hydrolyzed oligosaccharides and monosaccharides. POPs exhibited three main molecular distribution of 601-620 kDa, 4.12-6.09 kDa, and 3.57-6.02 kDa. Hydrolyzed oligosaccharides with degree of polymerization (DP) 2-13 got primarily characterized by analyzing the rich fragmentation information obtained by hydrophilic interaction chromatography/ion mobility-quadrupole time-of-flight mass spectrometry (HILIC/IM-QTOF-MS). Amongst them, the DP5 oligosaccharide was characterized as 1,6,6-kestopentaose. The molecular ratio of Fru: Ara: Glc: Gal: Xyl was 87.72: 0.30: 11.56: 0.19: 0.23. In vitro fermentation demonstrated that 4.5 mg/mL of POPs could significantly promote the growth of L. johnsonii. Co-cultivated with 4.5 mg/mL of POPs, L. johnsonii exhibited stronger antimicrobial activity against Klebsiella pneumoniae. The concentrations of short-chain fatty acids in the POPs-lactobacilli fermented products, including acetic acid, isobutyric acid, and isovaleric acid, were increased. Conclusively, POPs represent the promising prebiotic candidate to facilitate lactobacilli, which is associated with exerting the health benefits.

Efficient Carrier Transport in 2D Bi2O2Se/CsBi3I10 Perovskite Heterojunction Enables Highly-Sensitive Broadband Photodetection.

2D Bi2O2Se has recently garnered significant attention in the electronics and optoelectronics fields due to its remarkable photosensitivity, broad spectral absorption, and excellent long-term environmental stability. However, the development of integrated Bi2O2Se photodetector with high performance and low-power consumption is limited by material synthesis method and the inherent high carrier concentration of Bi2O2Se. Here, a type-I heterojunction is presented, comprising 2D Bi2O2Se and lead-free bismuth perovskite CsBi3I10, for fast response and broadband detection. Through effective charge transfer and strong coupling effect at the interfaces of Bi2O2Se and CsBi3I10, the response time is accelerated to 4.1 µs, and the detection range is expanded from ultraviolet to near-infrared spectral regions (365-1500 nm). The as-fabricated photodetector exhibits a responsivity of 48.63 AW-1 and a detectivity of 1.22×1012 Jones at 808 nm. Moreover, efficient modulation of the dominant photocurrent generation mechanism from photoconductive to photogating effect leads to sensitive response exceeding 103 AW-1 for heterojunction-based photo field effect transistor (photo-FETs). Utilizing the large-scale growth of both Bi2O2Se and CsBi3I10, the as-fabricated integrated photodetector array demonstrates outstanding homogeneity and stability of photo-response performance. The proposed 2D Bi2O2Se/CsBi3I10 perovskite heterojunction holds promising prospects for the future-generation photodetector arrays and integrated optoelectronic systems.

Self-Catalyzed Hydrogenated Carbon Nano-Onions Facilitates Mild Synthesis of Transparent Nano-Polycrystalline Diamond.

Transparent nano-polycrystalline diamond (t-NPD) possesses superior mechanical properties compared to single and traditional polycrystalline diamonds. However, the harsh synthetic conditions significantly limit its synthesis and applications. In this study, a synthesis routine is presented for t-NPD under low pressure and low temperature conditions, 10 GPa, 1600 °C and 15 GPa, 1350 °C similar with the synthesis condition of organic precursor. Self-catalyzed hydrogenated carbon nano-onions (HCNOs) from the combustion of naphthalene enable synthesis under nearly industrial conditions, which are like organic precursor and much lower than that of graphite and other carbon allotropes. This is made possible thanks to the significant impact of hydrogen on the thermodynamics, as it chemically facilitates phase transition. Ubiquitous nanotwinned structures are observed throughout t-NPD due to the high concentration of puckered layers and stacking faults of HCNOs, which impart a Vickers hardness about 140 GPa. This high hardness and optical transparency can be attributed to the nanocrystalline grain size, thin intergranular films, absence of secondary phase and pore-free features. The facile and industrial-scale synthesis of the HCNOs precursor, and mild synthesis conditions make t-NPD suitable for a wide range of potential applications.

High-temperature superconductivity up to 223 K in the Al stabilized metastable hexagonal lanthanum superhydride.

As compressed hydrides constantly refresh the records of superconducting critical temperatures (Tc) in the vicinity of room temperature, this further reinforces the confidence to find more high-temperature superconducting hydrides. In this process, metastable phases of superhydrides offer enough possibilities to access superior superconducting properties. Here we report a metastable hexagonal lanthanum superhydride (P63/mmc-LaH10) stabilized at 146 GPa by introducing an appropriate proportion of Al, which exhibits high-temperature superconductivity with Tc ∼ 178 K, and this value is enhanced to a maximum Tc ∼ 223 K at 164 GPa. A huge upper critical magnetic field value Hc2(0) reaches 223 T at 146 GPa. The small volume expansion of P63/mmc-(La, Al) H10 compared with the binary LaH10 indicates the possible interstitial sites of Al atoms filling into the La-H lattice, instead of forming conventional ternary alloy-based superhydrides. This work provides a new strategy for metastable high-temperature superconductors through the multiple-element system.