Cerium-promoted conversion of dinitrogen into high-energy-density material CeN_(6) under moderate pressure

Synthesis pressure and structural stability are two crucial factors for highly energetic materials,and recent investigations have indicated that cerium is an efficient catalyst for N2 reduction reactions.Here,we systematically explore Ce–N compounds through first-principles calculations,demonstrating that the cerium atom can weaken the strength of the N≡N bond and that a rich variety of cerium polynitrides can be formed under moderate pressure.Significantly,P1-CeN_(6) possesses the lowest synthesis pressure of 32 GPa among layered metal polynitrides owing to the strong ligand effect of cerium.The layered structure of P1-CeN_(6) proposed here consists of novel N_(14) ring.To clarify the formation mechanism of P1-CeN_(6),the reaction path Ce+3N2→trans-CeN_(6)→P1-CeN_(6) is proposed.In addition,P1-CeN_(6) possesses high hardness(20.73 GPa)and can be quenched to ambient conditions.Charge transfer between cerium atoms and N_(14) rings plays a crucial role in structural stability.Furthermore,the volumetric energy density(11.20 kJ/cm^(3))of P1-CeN_(6) is much larger than that of TNT(7.05 kJ/cm^(3)),and its detonation pressure(128.95 GPa)and detonation velocity(13.60 km/s)are respectively about seven times and twice those of TNT,and it is therefore a promising high-energy-density material.

Pressure-induced stable structures and physical properties of Sr–Ge system

We have systematically investigated the structures of Sr-Ge system under pressures up to 200 GPa and found six stable stoichiometric structures,they being Sr_(3)Ge,Sr_(2)Ge,SrGe,SrGe_(2),SrGe_(3),and SrGe_(4).We demonstrate the interesting structure evolution behaviors in Sr-Ge system with the increase of germanium content,Ge atoms arranging into isolated anions in Sr_(3)Ge,chains in Sr_(2) Ge,square units in SrGe,trigonal units and hexahedrons in SrGe_(2),cages in SrGe_(3),hexagons and Geg rings in SrGe_(4).The structural diversity produces various manifestations of electronic structures,which is of benefit to electrical transportation.Among them,these novel phases with metallic structures show superconductivity(maximum T_(c)~8.94 K for Pmmn Sr_(3)Ge).Notably,the n-type semiconducting Pnma SrGe_(2) structure exhibits high Seebeck coefficient and excellent electrical conductivity along the y direction,leading to a high ZT value up to 1.55 at 500 K,which can be potential candidates as high-performance thermoelectrics.Our results will enable the development of fundamental science in condensed matter physics and potential applications in novel electronics or thermoelectric materials.

Measuring Grfuneisen Parameter of Lead by High Pressure-Jump Method

Using the technology of pressure jump, variations of temperature associated with pressure from 2.4 GPa to 4.6 GPa are measured for lead. The Grfuneisen parameter is calculated from the thermodynamic relation γ =（Ks/T）（aT/aP）s, in which substitution of △T/△P for aT/aP at median pressure is strictly justified. The correction of temperature change is carried out by analysing the experimental data, which makes the process more approaching to an adiabatic condition. The calculated values of △T/ △ P and γ gradually decrease with the increasing pressure. The decrease trend is consistent with the previous work. The γ values in the range of 2-3 GPa are averagely higher than the results of Ramakrishnan et al., indicating the effect of temperature correction. The improved method is promising for measurements of Grfineisen parameter to higher pressure range.

Preparation of High-Density Nanocrystalline Bulk Selenium by Rapid Compressing of Melt

The melt＇s solidification behavior of elemental selenium is investigated by a series of experiments including rapid compressing to 2.8 and 3.5 GPa within 20ms respectively, slow compressing to 2.8 GPa for 20 min and natural cooling at ambient pressure. Based on the x-ray diffraction, scanning electron microscope and transmission electron microscope results of the recovered samples, it is clearly shown that homogenous nanostructures are formed only by the rapid compression processes, and that the average crystal sizes are about 18.7 and 19.0 nm in the samples recovered from 2.8 and 3.5 GPa, respectively. The relative density of the nanocrystalline bulk reaches 98.17% of the theoretical value. It is suggested that rapid compression could induce pervasive nucleation and restrain grain growth during the solidification, which is related to fast supercooling, higher viscosity of the melt and lower diffusivity of atoms under high pressure.

Effect of Increasing Course of Temperature and Pressure on Polypropylene Degradation in Supercritical Water

在聚丙烯(PP ) 上增加温度和压力的路线的效果超级批评的水里的降级为开发再循环浪费塑料的一个过程被调查。一组实验被路线一为 30min ， 70min ，和 120min 在 26MPa ， 380 °C 的温度或 400 °C 的一个压力在一个反应系统执行(温度和压力的增加的功课经由到超级批评区域的气体的区域)，并且另外的组被路线二以相应成立条件执行(温度和压力的增加的功课经由到超级批评区域的液体区域)。增加的功课的时间关于 30min。产品被 Ostward 类型粘度计，气体的层析，和集体分光计(GC/MS ) 分析。描述结果建议温度和压力的不同增加功课将产生不同结果，尽管他们在类似的成立条件下面被对待。路线二在超级批评的水里的 PP 降级上是更有效的，这也被发现。

Highly Robust Reentrant Superconductivity in CsV_3Sb_5 under Pressure

We present the superconducting(SC) property and high-robustness of structural stability of kagome CsV_3Sb_5 under in situ high pressures.For the initial SC-I phase,its T_c is quickly enhanced from 3.5 K to 7.6 K and then totally suppressed at P-10 GPa.With further increasing pressure,an SC-Ⅱ phase emerges at P-15 GPa and persists up to 100 GPa.The T_c rapidly increases to the maximal value of 5.2 K at P=53.6 GPa and slowly decreases to 4.7 K at P=100 GPa.A two-dome-like variation of T_c in CsV_3Sb_5 is concluded here.The Raman measurements demonstrate that weakening of E_(2g) mode and strengthening of E_(1g) mode occur without phase transition in the SC-II phase,which is supported by the results of phonon spectra calculations.Electronic structure calculations reveal that exertion of pressure may bridge the gap of topological surface nontrivial states near E_F,i.e.,disappearance of Z2 invariant.Meanwhile,the Fermi surface enlarges significantly,consistent with the increased carrier density.The findings here suggest that the change of electronic structure and strengthened electron-phonon coupling should be responsible for the pressure-induced reentrant SC.

Novel Superconducting Electrides in Ca–S System under High Pressures

Due to their unique structure properties,most of the electrides that possess extra electrons locating in interstitial regions as anions are insulators.Metallic and superconducting electrides are very rare under ambient conditions.We systematically search possible compounds in Ca-S systems stabilized under various pressures up to 200 GPa,and investigate their crystal structures and properties using first-principles calculations.We predict a series of novel stoichiometries in Ca-S systems as potential superconductors,including P2_(1)/m Ca_(3)S, Pnma Ca_(3)S,Pnma Ca_(2)S,Cmcm Ca_(2)S,Fddd CaS_(2),Immm CaS_(3) and C2/c CaS_(4).The P4mbm Ca_(3)S phase exhibits a maximum Tc value of ~20K.It is interesting to notice that the P2_(1)/m Ca_(3)S and Pnma Ca_(2)S stabilized at 60 and 50 GPa behave as superconducting electrides with critical temperatures Tc of 7.04 K and 0.26 K,respectively.More importantly,our results demonstrate that P2_(1)/m Ca_(3)S and Pnma Ca_(2)S are dynamically stable at 5 GPa and 0 GPa,respectively,indicating a high possibility to be quenched to ambient condition or synthesized using the large volume press.

Synthesis of Highly Stable One-Dimensional Black Phosphorus/h-BN Heterostructures:A Novel Flexible Electronic Platform

Layered black phosphorus(BP)has recently emerged as a promising semiconductor because of its tunable band gap,high carrier mobility and strongly in-plane anisotropic properties.One-dimensional(1 D)BP materials are attractive for applications in electronic and thermal devices,owing to their tailored charge and phonon transports along certain orientations.However,the fabrication of 1 D BP materials still remains elusive thus far.We herein report the successful synthesis and characterization of nanotube-like BP for the first time by a selective composite with hexagonal boron nitride(h-BN)nanotubes under high pressure and high temperature conditions.The produced 1 D BP/h-BN composites possess flexible diameter,length and thickness by adjusting the experimental synthesis parameters.Interestingly,it is important to notice that the stability of our BP sample has been significantly improved under the formation of heterostructures,which can actively promote their commercial applications.Our experimental work,together with first-principles calculations,presents a new scalable strategy of designing 1 D tube-like BP/h-BN heterostructures that are promising candidates for flexible and high efficiency electronic platform.

Multi-Shock Compression of Dense Hydrogen-Helium Mixture Beyond 100 GPa

为准备稠密的气体的样品的一个低温实验法的目标系统在一支二阶段的轻气体的枪上被建立并且被使用借助于 multi-shocktechnique 在更高的压力并且在高温度学习州的 ofhydrogen 氦混合的方程。记录光放射信号清楚地显示 thethird- 的开始的时刻，第四 -- ，第六 -- ，第八 -- ，并且第十吃惊处理，它在对直到 104 GPa 的观察最终的状态的 Mansoori-Canfield-Ross 变化不安理论的预言的好同意。

Characteristics of the Seismic Waves from a New Active Source Based on Methane Gaseous Detonation

Active seismic sources are critical for obtaining high resolution images of the subsurface.For active imaging in urban areas,environment friendly and green seismic sources are required.In present work,we introduce a new type of green active source based on the gaseous detonation of methane and oxygen.When fired in a closed container,the chemical reaction,i.e.gaseous detonation,will produce high pressure air over 150 MPa.Seismic waves are produced when high pressure air is quickly released to impact the surroundings.The first field experiment of this active source was carried out in December,2017 in Jingdezhen,Jiangxi Province,where a series of active sources were excited to explore their potential in mine exploration.In current work,we analyzed the seismic waves recorded by near-field accelerators and a dense short-period seismic array and compared them with those from a mobile airgun source,another kind of active source by releasing high pressure air into water.The results demonstrate that it can be used for high resolution near surface imaging.Firstly,the gaseous detonation productions are harmless CO2 and water,making it a green explosive source.Secondly,the dominant seismic frequencies are 10-80 Hz and a single shot can be recorded up to 15 km,making it suitable for local structure investigations.Thirdly,it can be excited in vertical wells,similar to traditional powder explosive sources.It can also act as an additional on-land active source to airgun sources,which requires a suitable water body as intermediate media to generate repeating signals.Moreover,the short duration and high frequency signature of the source signals make it safe with no damage to nearby buildings.These make it convenient to excite in urban areas.As a new explosive source,the excitation equipment and conditions,such as gas ratio,sink depth and air-releasing directions,need further investigation to improve seismic wave generation efficiency.

Preparation of Thermo-Stable Bulk Metallic Glass of Nd10Cu20Ni10Al10 by Rapid Compression

Melt of Nd60Cu20NiloAl10 alloy is solidified by rapid compression from 0.1 to 5.5 GPa at 793K and from 0.1 to 3.2GPa at 873K within 20ms, separately. A fully bulk metallic glass is obtained by the rapid compression method. By comparing with as-cast bulk metallic glass （BMG）, it is found that Nd60Cu20Ni10Al10 BMG prepared by rapid compression exhibits a higher thermodynamic stability and a paramagnetic property. The relationship between the glass-formation temperature and the pressure in rapid compression for the BMG is demonstrated in the P - T phase diagram.

Measurement on Effective Shear Viscosity Coefficient of Iron under Shock Compression at 100 GPa

The oscillatory damping curve of a shock front propagating in iron shocked to 103 GPa is measured by use of two-stage light-gas gun and electric pin techniques. The corresponding effective shear viscosity coefficient is deduced to be about 2000 Pa.s from Miller and Ahrens＇ formula. The result is consistent with that of Mineev＇s data at 31GPa, while it is higher by five orders than the predictions based on the static measurements at about 5 GPa and 2000K and molecular dynamic simulation up to 135-375 GPa and 4300-6000 K, and the discussions are presented.

Stable Compositions, Structures and Electronic Properties in K–Ga Systems Under Pressure

New stable stoichiometries in K-Ga systems are firstly investigated up to 100 GPa by the unbiased structure searching techniques.Six novel compositions as K4Ga,K3Ga,K2Ga,KGa,KGa2 and KGa4 are found to be thermodynamically stable under pressure.Most of the predicted stable phases exhibit metallic character,while the Fd3m KGa phase behaves as a semiconductor with a bandgap ~1.62 eV.Notably,the gallium atoms exhibit different interesting morphologies;e.g.,Ga2 units,zigzag chains,six rings and cage.We further investigate the bonding nature of K-Ga systems with help of electron localization function and Bader charge analyses.Strong covalent bonding characteristics are found between the Ga and Ga atoms,and ionic bonding patterns are observed between the K and Ga atoms.Meanwhile,we notice charge transferring from the K atom to the Ga atom in the K-Ga systems.The present results can be helpful for understanding the diverse structures and properties of K-Ga binary compounds at high pressures.

Effect of Iodine Additive on Thermostability of Bulk Amorphous Sulfur Prepared by Rapid Compression

Bulk amorphous sulfur(a-S)with 1 mol%of phosphorus,selenium and iodine additives and bulk amorphous pure sulfur samples were prepared by rapidly compressing the melts to 2 GPa within 20 ms.The results of x-ray diffraction,differential scanning calorimetry and in situ wide angle x-ray scattering of the recovered samples are presented and discussed.In the iodine doping case,obvious inhibiting effects on the crystallization and the melting process under high temperatures occurred,as well as on the structure relaxation of a-S at room temperature,suggesting that the thermal stability of amorphous sulfur is remarkably improved by the introduction of iodine additives.

Reply to Comment on ‘Multi-shock Compression of Dense Hydrogen-Helium Mixture beyond 100 GPa＇

The data analysis method for the multi-shock experiments and the EOS model used in our recent Letter are inconsistent with what the comment conjectures and claims.

Diffusionless-Like Transformation Unlocks Pseudocapacitance with Bulk Utilization: Reinventing Fe_(2)O_(3) in Alkaline Electrolyte

Energy density can be substantially raised and even maximized if the bulk of an electrode material is fully utilized.Transition metal oxides based on conversion reaction mechanism are the imperative choice due to either constructing nanostructure or intercalation pseudocapacitance with their intrinsic limitations.However,the fully bulk utilization of transition metal oxides is hindered by the poor understanding of atomic-level conversion reaction mechanism,particularly it is largely missing at clarifying how the phase transformation(conversion reaction)determines the electrochemical performance such as power density and cyclic stability.Herein,α-Fe_(2)O_(3) is a case provided to claim how the diffusional and diffusionless transformation determine the electrochemical behaviors,as of its conversion reaction mechanism with fully bulk utilization in alkaline electrolyte.Specifically,the discharge productα-FeOOH diffusional from Fe(OH)2 is structurally identified as the atomic-level arch criminal for its cyclic stability deterioration,whereas the counterpartδ-FeOOH is theoretically diffusionless-like,unlocking the full potential of the pseudocapacitance with fully bulk utilization.Thus,such pseudocapacitance,in proof-of-concept and termed as conversion pseudocapacitance,is achieved via diffusionless-like transformation.This work not only provides an atomic-level perspective to reassess the potential electrochemical performance of the transition metal oxides electrode materials based on conversion reaction mechanism but also debuts a new paradigm for pseudocapacitance.

Exothermic Supercooled Liquid-Liquid Transition in Amorphous Sulfur

非结晶的硫(作为) 被很快压缩熔融的硫高迫使准备。从微分扫描热量计大小，一座大发热的山峰在 396 K 附近被观察了。联机 wide-angled X 光散布系列显示没有结晶化发生在温度范围 295453 K，建议 exothermal 过程对应于 amorphous-to-amorphous 转变。到液体硫的从非结晶的硫的转变被硫的直接观察进一步验证融化在联系转变的温度。这是直接向液体硫作为变换汇报那的第一次，它避免了一个结晶化过程。而且，转变是一发热并且卷扩大进程。

An Investigation on Polypropylene Degradation in Supercritical Water Adding Benzoyl Peroxide

The effect of benzoyl peroxide (BPO) on polypropylene (PP) degradation in supercritical water was investigated with the aim of developing a process for recycling of waste plastics. A series of experiments with and without BPO were carried out at temperatures of 653 K and 673 K under pressure about 26 MPa for 30, 75 and 120 min respectively. Products were analyzed by an Ostward-type viscometer, gas chromatography and spectrometry (GC/MS) etc. The results indicated that mean molecular weight of the samples decreased greatly along with the time elapsing or with the temperature increasing, and PP was decomposed to aliphatic and cycloparaffinic hydrocarbons but a few benzenoid hydrocarbons. By comparing the experiments with and without BPO, it was made clear that BPO is an effective additive on PP degradation in supercritical water.

地球深处形成含硼金刚石的可行机制

近年来,以“希望之钻”为代表天然蓝色钻石(蓝钻)的形成机制引起科学界和大众的广泛兴趣.天然蓝钻是形成于地球最深处的珍贵矿物,含约0.011~10μg/g棚杂质.现行地球化学模型表明地球内部硼元素主要富集于大陆和大洋地壳,极难进入地球内部的下地幔深度.蓝钻的存在为地球下地幔环境中存在硼元素提供了有力证据,然而其地质起源与循环机制是当前领域内亟待解决的科学难题之一.在本研究中,我们提出金属硼化物随地球板块运动进入下地幔深处,在高温高压环境下与碳酸盐发生氧化还原反应,从而形成蓝钻的物理机制.通过第一性原理计算提出了多种可能形成蓝钻的化学反应途径,并在下地幔压力与温度条件下(22.5 GPa,2100 K),利用CaCO_(3)和FeB的直接氧化还原反应,成功制备“类天然”蓝钻.这一发现揭示了地球深处蓝钻形成之谜,并为进一步深入探索地球内部的物质循环和矿物形成机制提供了新思路.

Screening for new thermoelectric material: A semiconducting TaS_(3) with nanoporous structure

Transition-metal sulfides,such as 1T-and 2H-TaS_(2),are attracting considerable interest in modern condensed matter physics for their diverse behaviors of the Mott state,peculiar charge-density-wave phase and superconductivity.The intrinsically low thermal conductivities along the cross-plane direction can advantage the potential high thermoelectric performance;yet,their insignificant power factors severely hampered the practical applications as thermoelectric devices.In this perspective,we herein present a new semiconducting phase in TaS_(3) with the space group C2/m predicted by the swarmintelligence structure-searching method.The C2/m-TaS_(3) phase exhibits anisotropic multivalley band dispersions,which is beneficial for electronic transport.Meanwhile,the unique structure within nanopores leads to strong anharmonic scattering,significantly reducing the lattice thermal conductivity.As a result,the calculated figure of merit ZT can reach up to 1.68 and 1.57 at 800 K for p-and n-type,respectively that is comparable with conventional thermoelectric materials(e.g.PbTe,Bi_(2)Te_(3)).Therefore,our calculation reveals that the C2/m-TaS_(3) phase can be a potential high-performance candidate as nontoxic and eco-friendly thermoelectrics,and will stimulate further experimental exploration for understanding and tailoring thermoelectric capability in related transition-metal sulfides.