Shock Induced Emission from Sapphire in High-Pressure Phase of Rh2O3 （Ⅱ） Structure

A distinct optical emission from the Rh203 （Ⅱ） structural sapphire is observed under shock compression of 125, 132, and 143 GPa. The emission intensity continuously increases with the thickness of shocked sapphire. The colour temperature is determined to be about 4000 K, which is obviously smaller than the reported value of the alpha phase alumina at the pressures below 80 GPa. The present results suggest that the structural transformation will cause an obvious change of optical property in sapphire.

Structural evolution and molecular dissociation of H_(2)S under high pressures

Solid H_(2)S as the precursor for H_(3)S with incredible superconducting properties under high pressure,has recently attracted extensive attention.Here in this work,we propose two new phases of H_(2)S with P42/n and I41/a lattice symmetries in a pressure range of 0 GPa–30 GPa through first-principles structural searches,which complement the phase transition sequence.Further an ab initio molecular dynamics simulation confirms that the molecular phase P2/c of H_(2)S is gradually dissociated with the pressure increasing and reconstructs into a new P2_(1)/m structure at 160 GPa,exhibiting the superconductivity with Tc of 82.5 K.Our results may provide a guidance for the theoretical study of low-temperature superconducting phase of H_(2)S.

First-principles study of electronic and magnetic properties of Fe atoms on Cu_(2)N/Cu(100)

First-principles calculations were conducted to investigate the structural,electronic,and magnetic properties of single Fe atoms and Fe dimers on Cu_(2)N/Cu(100).Upon adsorption of an Fe atom onto Cu_(2)N/Cu(100),robust Fe-N bonds form,resulting in the incorporation of both single Fe atoms and Fe dimers within the surface Cu_(2)N layer.The partial occupancy of Fe-3d orbitals lead to large spin moments on the Fe atoms.Interestingly,both single Fe atoms and Fe dimers exhibit in-plane magnetic anisotropy,with the magnetic anisotropy energy(MAE)of an Fe dimer exceeding twice that of a single Fe atom.This magnetic anisotropy can be attributed to the predominant contribution of the component along the x direction of the spin-orbital coupling Hamiltonian.Additionally,the formation of Fe-Cu dimers may further boost the magnetic anisotropy,as the energy levels of the Fe-3d orbitals are remarkably influenced by the presence of Cu atoms.Our study manifests the significance of uncovering the origin of magnetic anisotropy in engineering the magnetic properties of magnetic nanostructures.

Unveiling the pressure-driven metal–semiconductor–metal transition in the doped TiS_(2)

Conventional theories expect that materials under pressure exhibit expanded valence and conduction bands,leading to increased electrical conductivity.Here,we report the electrical properties of the doped 1T-TiS_(2) under high pressure by electrical resistance investigations,synchrotron x-ray diffraction,Raman scattering and theoretical calculations.Up to 70 GPa,an unusual metal-semiconductor-metal transition occurs.Our first-principles calculations suggest that the observed anti-Wilson transition from metal to semiconductor at 17 GPa is due to the electron localization induced by the intercalated Ti atoms.This electron localization is attributed to the strengthened coupling between the doped Ti atoms and S atoms,and the Anderson localization arising from the disordered intercalation.At pressures exceeding 30.5 GPa,the doped TiS_(2) undergoes a re-metallization transition initiated by a crystal structure phase transition.We assign the most probable space group as P2_(1)2_(1)2_(1).Our findings suggest that materials probably will eventually undergo the Wilson transition when subjected to sufficient pressure.

A Strength Softening Phase Transition Observed in Shocked （Mg0.92,Fe0.08）SiO3 Perovskite at About 83 GPa

We report the experimental data of Hugoniot longitudinal sound velocity VL for natural （Mg0.92,Fe0.08）SiO3 enstatite sample at about 40-140 GPa, consisting of three new data and five previously reported data but revised by our new Hugoniot equation of state parameters. Three segments, separated by two discontinuities, appear in the VL-PH （shock pressure） plot. Analyses show that the first discontinuity at about 64 GPa, with a sharp increase of VL of about 21%, is judged to be a phase transition from enstatite to Pbnm perovskite （PV）; while the second one at about 83 GPa, with a dramatic decrease of VL of about 23%, is likely caused by a subtle structural change from Pbnm PV to tetragonal PV, accompanied by material strength softening due to melting of oxygen sublattices. This strength softening evidence is obtained first from shock wave experiments, and probably has profound implications for probing into the origin of low seismic velocity anomaly in the Earth＇s lower mantle and thus constraining the geophysical and geochemical models for the Earth＇s lower mantle.

High T_(c) Superconductivity in Heavy Rare Earth Hydrides

Sulfur and lanthanum hydrides under compression display superconducting states with high observed critical temperatures.It has been recently demonstrated that carbonaceous sulfur hydride displays room temperature superconductivity.However,this phenomenon has been observed only at very high pressure.Here,we theoretically search for superconductors with very high critical temperatures,but at much lower pressures.We describe two of such sodalite-type clathrate hydrides,YbH6 and LuH6.These hydrides are metastable and are predicted to superconduct with T_(c)~145 K at 70 GPa and T_(c)~273 K at 100 GPa,respectively.This striking result is a consequence of the strong interrelationship between the f states present at the Fermi level,structural stability,and the final T_(c) value.For example,TmH6,with unfilled 4f orbitals,is stable at 50 GPa,but has a relatively low value of T_(c) of 25 K.The YbH6 and LuH6 compounds,with their filled f-shells,exhibit prominent phonon"softening",which leads to a strong electron-phonon coupling,and as a result,an increase in T_(c).

First-principles study on the conventional superconductivity of N-doped fcc-LuH_(3)

Recently,room-temperature superconductivity has been reported in a nitrogen-doped lutetium hydride at near-ambient pressure[Dasenbrock-Gammon et al.,Nature 615,244(2023)].The superconducting properties might arise from Fm3m-LuH_(3)−δNε.Here,we systematically study the phase diagram of Lu–N–H at 1 GPa using first-principles calculations,and we do not find any thermodynamically stable ternary compounds.In addition,we calculate the dynamic stability and superconducting properties of N-doped Fm3m-LuH_(3) using the virtual crystal approximation(VCA)and the supercell method.The R3m-Lu_(2)H_(5)N predicted using the supercell method could be dynamically stable at 50 GPa,with a T_(c) of 27 K.According to the VCA method,the highest T_(c) is 22 K,obtained with 1%N-doping at 30 GPa.Moreover,the doping of nitrogen atoms into Fm3m-LuH_(3) slightly enhances T_(c),but raises the dynamically stable pressure.Our theoretical results show that the T_(c) values of N-doped LuH_(3) estimated using the Allen–Dynes-modified McMillan equation are much lower than room temperature.

Surface Leakage Currents in SiN and Al_2O_3 Passivated AlGaN/GaN High Electron Mobility Transistors

Surface leakage currents of A1GaN/GaN high electron mobility transistors are investigated by utilizing a circular double-gate structure to eliminate the influence of mesa leakage current. Different mechanisms are found under various passivation conditions. The mechanism of the surface leakage current with AI2 03 passivation follows the two-dimensional variable range hopping model, while the mechanism of the surface leakage current with SiN passivation follows the Frenkel-Poole trap assisted emission. Two trap levels are found in the trap-assisted emission. One trap level has a barrier height of 0.22eV for the high electric field, and the other trap level has a barrier height of 0.12eV for the low electric field.

Detection of DNA Mutations Using Novel SERS （Surface-Enhanced Raman Spectroscopy） Diagnostic Platform

This article describes the detection of DNA mutations using novel Au-Ag coated GaN substrate as SERS （surface-enhanced Raman spectroscopy） diagnostic platform. Oligonucleotide sequences corresponding to the BCR-ABL （breakpoint cluster region-Abelson） gene responsible for development of chronic myelogenous leukemia were used as a model system to demonstrate the discrimination between the wild type and Met244Val mutations. The thiolated ssDNA （single-strand DNA） was immobilized on the SERS-active surface and then hybridized to a labeled target sequence from solution. An intense SERS signal of the reporter molecule MGITC was detected from the complementary target due to formation of double helix. The SERS signal was either not observed, or decreased dramatically for a negative control sample consisting of labeled DNA that was not complementary to the DNA probe. The results indicate that our SERS substrate offers an opportunity for the development of novel diagnostic assays.

Interplay between cold densification and malic acid addition (C4H6O5) for the fabrication of near-isotropic MgB2 conductors for magnet application

The effect of cold high pressure densification(CHPD)on anisotropy of the critical current density(Jc)in《in situ》single core binary and alloyed MgB2 tapes has been determined as a function of temperatures at 4.2 K,20 K and 25 K as well as at applied magnetic fields up to 19 T.The study includes binary and C4H6O5(malic acid)doped MgB2 tapes before and after CHPD.It is remarkable that the CHPD process not only improved the Jc values,in particular at the higher magnetic fields,but also decreased the anisotropy ratio,Г=JC^///JC^⊥In binary MgB2 tapes,the anisotropy factor F increases with higher aspect ratios,even after applying CHPD.In malic acid(C4H6O5)doped tapes,however,the application of CHPD leads only to small enhancements ofГ,even for higher aspect ratios.This is attributed to the higher carbon content in the MgB2 filaments,which in turn is a consequence of the reduced chemical reaction path in the densified filaments.At all applied field values,it was found that CHPD processed C4H6O5 doped tapes exhibit an almost isotropic behavior.This constitutes an advantage in view of industrial magnet applications using wires with square or slightly rectangular configuration.

Re-emergence of superconductivity via pressure-induced Lifshitz transition in preserved 6R-TaS_(2) crystal structure

Investigating the implications of interlayer coupling on superconductivity is vital for comprehending the intrinsic mechanisms of two-dimensional materials.Van der Waals heterojunctions have attracted extensive research owing to their exotic interlayer coupling.In this study,we investigated the natural heterostructure superconductor featuring 6R-TaS_(2) via measurements of electrical resistance,the Hall effect,and in-situ synchrotron X-ray diffraction(XRD)under various pressures.The study findings show that the superconducting transition temperature(T_(c))of 6R-TaS_(2) in the range of 0-32.5 GPa exhibits an unusual double-dome behavior as a function of pressure,with the first and second domes in the pressure range of 0-5.3 and 6.8-32.5 GPa,respectively.At 56.6GPa,a new superconducting phase with a T_(c) of 2 K was observed.The XRD results show that the singular evolution of the T_(c) is independent of the structural phase transition.Combining the XRD results,first-principles calculations,and Hall effect measurements,we found that different interlayer coupling effects resulted in double dome superconductivity and the re-emergence of superconducting.Our findings shed light on the pivotal role of interlayer coupling in driving the anomalous alterations in superconducting properties triggered by charge transfer and Fermi surface reconstruction and provide an alternative route for comprehending the mechanisms of superconductivity in transition metal dichalcogenides(TMDs).

High temperature superconductor Na_(2)B_(2)H stabilized by hydrogen intercalation under ambient pressure

Hydrogenated metal borides have attracted much attention due to their potential high-temperature superconductivity.Here,we propose a new strategy for hydrogen intercalation tuning the stability and superconductivity of the boron honeycomb sublattice,and predict an unprecedented layered compound Na_(2)B_(2)H,which hosts excellent superconductivity.Strikingly,the superconducting transition temperature(Tc)of Na_(2)B_(2)H reaches 42 K at ambient pressure.The Tcvalue can be further increase to 63 K under 5%biaxial tensile strain.The excellent superconductivity originates from the strong electron-phonon coupling between theσ-bonding bands near the Fermi level and the B-B stretching optical E modes.The interstitial electron localization and crystal orbitals of the H-intercalated Na ion layer well match the boron honeycomb lattice and act as a chemical template to stabilize the B layer.Furthermore,the introduction of hydrogen tuned the Fermi level,and the coupling vibration of Na and H ions effectively enhanced the dynamic stability of the structure.Na_(2)B_(2)H represents a new family of layered high-temperature superconductors,and the strategy of stabilizing the honeycomb boron sublattice via chemical template hosts great potential for application to more layered compounds.

High Nitrogen Pressure Solution (HNPS) growth of GaN on 2 inch free standing GaN substrates

Recent results of High Nitrogen Pressure Solution (HNPS) growth of GaN crystals deposited on and separated from 2 inch,and smaller,GaN substrates grown by Hydride Vapor Phase Epitaxy (HVPE) have been presented. The influence of the c-plane bowing in the initial substrate on quality,rate and mode of growth by HNPS method has been analyzed in details.

Recent progress in MgB_(2)superconducting joint technology

Magnesium diboride(MgB_(2))magnets have the potential to be the next-generation liquid-helium-free magnet for magnetic resonance imaging(MRI)application due to their relatively high superconducting transition temperature,high current density and low raw material cost compared with current commercial niobium-titanium(Nb-Ti)magnets.A typical superconducting magnet includes several coils.To produce an ultra-stable magnetic field for imaging in MRI,a superconducting electromagnet operating in a persistent mode is crucial.Superconducting coils of the electromagnet in MRI are short-circuited to operate in the persistent mode by connecting coils with superconducting joints.Per-sistent joints have been demonstrated for in-situ and ex-situ wires of both mono-and multi-filamentary structures,made predominantly by PIT techniques similar to those used in wire production.To realise further engagement of MgB_(2)in MRI applications,enhancing the performance of MgB_(2)superconducting joints is essential.This literature review summarises research and development on MgB_(2)superconducting joining technology.

Cubic H_(3)S stabilized by halogens:High-temperature superconductors at mild pressure

Superconductivity in compressed sulfur hydride(H_(3)S)at above 200 K has attracted great interest in the study of hydrogen-based superconductors.However,the pressure required to stabilize H_(3)S is 150 GPa,posing significant challenges for experiments.Therefore,it is essential to find a strategy to reduce this pressure.In this study,by introducing halogen atoms into the H-S system,we discovered that hydrogen-based superconductors of H_(6)SX(X=Cl and Br)can be dynamically stable at mild pressures(5 GPa for H_(6)SCl and H_(6)SBr),as confirmed by first-principles calculations.Through the analysis of the bond properties,we revealed that introducing halogen elements would strengthen the H–S covalent bonds to reduce the dynamically stable pressure of H_(3)S.Our study provides a scheme to reduce the superconducting pressure of hydrogen-based superconductors.

High T_(c) superconductivity in layered hydrides XH_(15) (X = Ca, Sr, Y, La) under high pressures

The theoretical predictions and experimental synthesis of H_(3)S and LaH_(10) superconductors with record high superconducting transition temperatures(T_(c))have promoted the hydrogen-based superconducors to be a research hotspot in the field of solid-state physics.Here,we predict an unprecedented layered structure CaH15,with high T_(c) of 189 K at 200 GPa using ab initio calculations.As concerns the novel structure,one layer is made of a hydrogen nonagon,the other layer consists of a Ca atom and six H_(2) molecular units surrounding the Ca atom.This layered structure was also found in SrH_(15),YH_(15),and LaH_(15) at high pressures,each materials exhibit high T_(c) especially YH_(15) can reach above 200 K at 220 GPa.It represents the second class of layered superhydrides with high value of Tc after pentagraphene like HfH10.

Sound Velocities in Porous Iron Shocked to 177GPa and the Implications for Shock Melting

Sound velocities in shock-loaded solids are not only important to determine bulk moduli of solids at high pressures, but are also crucial to inform the shock melting of solids upon loading. In this letter, we first report on shock melting of porous solids at high pressures by measuring sound velocities in the porous iron of average density 6.90 g/cm^(3) in the pressure range of 110-180 GPa. The measured sound velocity softens at pressures from 122 to 156 Gpa, which may be attributed to shock melting of the porous iron.

Ternary superconducting hydrides stabilized via Th and Ce elements at mild pressures

The discovery of covalent H_(3)S and clathrate structure LaH_(10) with excellent superconducting critical temperatures at high pressures has facilitated a multitude of research on compressed hydrides.However,their superconducting pressures are too high(generally above 150 GPa),thereby hindering their application.In addition,making room-temperature superconductivity close to ambient pressure in hydrogen-based superconductors is challenging.In this work,we calculated the chemically“pre-compressed”Be-H by heavy metals Th and Ce to stabilize the superconducting phase near ambient pressure.An unprecedented ThBeH_(8)(CeBeH_(8))with a“fluorite-type”structure was predicted to be thermodynamically stable above 69 GPa(76 GPa),yielding a T_(c) of 113 K(28 K)decompressed to 7 GPa(13 GPa)by solving the anisotropic Migdal–Eliashberg equations.Be-H vibrations play a vital role in electron–phonon coupling and structural stability of these ternary hydrides.Our results will guide further experiments toward synthesizing ternary hydride superconductors at mild pressures.

High-pressure synthesis,mechanical properties,and oxidation behavior of advanced boron-containingα/β-Si_(3)N_(4)/Si ceramics using polymer-derived amorphous SiBN ceramics

The preparation of dense Si_(3)N_(4)-based ceramics has attracted great attention because of the achievable improvements in their mechanical properties and high-temperature oxidation resistance.In this work,advanced dense boron-containingα/β-Si_(3)N_(4)/Si monoliths were prepared via a high pressure‒high temperature technique in which polymer-derived amorphous SiBN powders were used as raw materials.The crystallization behavior and phase transformation of the polymer-derived amorphous samples were studied in the temperature range from 1400 to 1800℃.The results demonstrate that the incorporation of boron in the Si_(3)N_(4)matrix suppresses the phase transformation fromα-Si_(3)N_(4)toβ-Si_(3)N_(4).Furthermore,the mechanical properties of the as-prepared samples were measured,and the maximum hardness and fracture toughness of boron-rich SiBN samples reached 14.8 GPa and 7.96 MPa·m1/2,respectively.The hardness of the obtained boron-rich SiBN samples is stable up to 300℃.In addition,the oxidation behavior of the samples prepared at 1400 and 1600℃ was investigated at 1400℃ for 50 h.The results show that the incorporation of boron significantly improved the oxidation resistance of the samples because of the formation of borosilicate/cristobalite.This work provides guidance for the synthesis of boron-containingα/β-Si_(3)N_(4)-based ceramics with excellent mechanical properties and oxidation resistance.