First principles study of pressure-induced magnetic transition in CrN

First principles calculation was performed using tight-binding LMTO method with local density approximation (LDA) and atomic sphere approximation (ASA) to understand the electronic properties of chromium nitride. The equilibrium geometries, the magnetic moment, the electronic band structure, the total and partial DOS are obtained under various pressures and are analyzed in comparison with the available experimental data. The most stable structure of CrN is NaCl structure in the FM state. A pressure-induced second order magnetic phase transition from ferromagnetic (FM) to non-magnetic (NM) at very high pressure of 0.5549 Mbar is predicted. Our results indicate that CrN can be used as a hydrogen storage material.     

在200 GPa冲击压强下铁是否会发生固-固相变？

 根据Grüneisen物态方程、Hugoniot内能守恒方程和最新发表的铁的热物理参数，计算了ε-(hcp)铁和液态铁的理论Hugoniot曲线。计算的Hugoniot曲线与最新修正的铁的实验数据[J Appl Phys, 2000, 88: 5496]在总体上符合很好，并且可以细分为两个部分：在约低于200 GPa的压强区，用ε-铁模型的计算结果与实验结果符合很好；在约高于260 GPa的压强区，用液态铁模型的计算结果与实验数据也符合得比较好；对介于200~260 GPa之间的压强区，则归属于由ε-铁向液态铁转变的混合相区。这意味着铁的Hugoniot曲线在约200 GPa处出现的微小偏折是由固-液相变引起的，从而否定了Brown [Geophy Res Lett, 2001, 28: 4339]提出的它是一次由ε-铁向另一个未知结构的某个固相铁的相转变的见解。     

Structure phase transformation and equation of state of cerium metal under pressures up to 51 GPa

This study presents high pressure phase transitions and equation of states of cerium under pressures up to 51 GPa at room temperature. The angle-dispersive x-ray diffraction experiments are carried out using a high energy synchrotron x-ray source. The bulk moduli of high pressure phases of cerium are calculated using the Birch–Murnaghan equation. We discuss and correct several previous controversial conclusions, which are caused by the measurement accuracy or personal explanation. The c/a axial ratio of ε-Ce has a maximum value at about 29 GPa, i.e., c/a ≈ 1.690.     

Morphological effect on electrochemical performance of nanostructural CrN

Size and morphology are critical factors in determining the electrochemical performance of the supercapacitor materials, due to the manifestation of the nanosize effect. Herein, different nanostructures of the CrN material are prepared by the combination of a thermal-nitridation process and a template technique. High-temperature nitridation could not only transform the hexagonal Cr₂O₃ into cubic CrN, but also keep the template morphology barely unchanged. The obtained CrN nanostructures, including (i) hierarchical microspheres assembled by nanoparticles, (ii) microlayers, and (iii) nanoparticles, are studied for the electrochemical supercapacitor. The CrN microspheres show the best specific capacitance (213.2 F/g), cyclic stability (capacitance retention rate of 96% after 5000 cycles in 1-mol/L KOH solution), high energy density (28.9 Wh/kg), and power density (443.4 W/kg), comparing with the other two nanostructures. Based on the impedance spectroscopy and nitrogen adsorption analysis, it is revealed that the enhancement arised mainly from a high-conductance and specific surface area of CrN microspheres. This work presents a general strategy of fabricating controllable CrN nanostructures to achieve the enhanced supercapacitor performance.     

Equation of state and structural characterization of Cu4I4{PPh2(CH2CH = CH2)}4 under pressure

Combined high pressure single crystal X-ray diffraction experiments and ab initio simulations based on the density functional theory have been performed on a copper(I) iodide cluster formulated [Cu₄I₄{PPh₂(CH₂CH?=?CH₂)}₄] under high pressure up to 5?GPa. An exhaustive study of compressibility has been done by means of determination of isothermal equations of state and structural changes with pressure at 298?K taking advantage of the single crystal is more precise than powder X-ray diffraction for this type of experiments. It allows us to report the evidence of the existence of an isostructural phase transition of second order at 2.3?GPa not detected so far.     

High pressure behavior and structural properties of transition metal carbides

A pressure induced structural phase transition from NaCl-type (B₁) to CsCl-type (B₂) structure has been predicted in transition metal carbides, namely TiC, ZrC, NbC, HfC, and TaC by using an interionic potential theory with modified ionic charge (Z_m ), which includes Coulomb screening effect due to d-electron. The phase transition pressure (P_T ) relies on large volume discontinuity in pressure–volume relationship, and identifies the structural phase transition from B₁ phase to B₂ phase. The variation of second-order elastic constants with pressure follows a systematic trend identical to that observed in other compounds of NaCl-type structure. The Born criterion for stability is found to be valid in transition metal carbides.     

The equation of state of triolein up to 1 GPa

In this paper, the compressibility studies of triolein up to 1 GPa at temperature range from 10°C to 50°C have been presented. The discontinuity of V(p) relation, characteristic for the first-order phase transition was observed. At higher temperatures (40°C and above), the time necessary for the phase transition rises considerably. Also the pressure–volume hysteresis due to the phase formation–decomposition cycle was enlarged.     

高压下物质性质的研究

概述了高压（力）下物质性质研究的方法、历史和最新发展。     

Structural, electronic, and magnetic properties of CrN under high pressure

The structural,electronic and magnetic properties of CrN under high pressure are investigated by first-principles calculations.The antiferromagnetic orthorhombic structure is identified to be the preferred ground state structure.It possesses a bulk modulus of 252.8 GPa and the nonzero magnetic moment of 2.33 μ B per Cr ion,which agree well with the experimental results.CrN undergoes structural and magnetic transitions from an antiferromagnetic rocksalt structure to a non-magnetic Pnma phase at 132 GPa.Under compression,the magnetic moment of the Cr ion reduces rapidly near the equilibrium and phase transition point,and the distribution of the density of states is broadened,but the form of overlap between the orbitals of Cr d and N p remains unchanged.The broadening of the band induces spin flipping,which consequently results in the smaller magnetic moment of the Cr ion.     

Thermoelastic behaviour of hexagonal graphite-like boron nitride

Abstract

A synchrotron X-ray diffraction study on hexagonal graphite-like boron nitride (h-BN) was performed under high pressures and temperatures. From the measured P-V-Trelation for h-BN (with a three-dimensional ordering parameter P₃ = 0.9) in the temperature range from 298 to 1273 K and up to 6.7 GPa, the thermoelastic parameters are derived by fitting a modified high temperature Birch-Murnaghan equation of state. The results are: bulk modulus B₀[GPa] = 27.6-0.0081(T[K]-298) and its pressure derivative B¹ = 10.5 + 0.0016(T [K] - 298). These values are for samples with P₃ = 0.9 and are quite different for samples with different values of the order parameter. This parameter is shown to have a leading role in the determination of the thermoelastic properties of h-BN, which explains and reconciles the differences between previous results.     

热膨胀型固体物态方程

根据晶体热振动的非谐振效应,推导出了一种热膨胀形式的固体物态方程.与常用的Gr櫣ｎｅｉｓｅｎ物态方程相比,该热膨胀物态方程在理论上说明了极高压下等熵线族趋近于冷压线的事实,并可很好地连接固体高压与常压性质.介绍了该物态方程的理论,定义了新的热力学函数,并对如何采用冲击Hugoniot方程拟合热膨胀形式的固体物态方程进行了介绍 关键词： 物态方程 固体 高压 热膨胀     

高温高压下碳的状态方程及相变理论研究

 研究了高温高压下三相碳（石墨、金刚石、液相碳）的状态方程，包括高压下石墨到金刚石的固-固相变以及高温下石墨和金刚石的熔解曲线。计算所得到的金刚石熔解曲线具有正的斜率，石墨-金刚石-液相三相点为4 400 K，14 GPa左右。     

High pressure behavior of alkaline earth tellurides

We have predicted high pressure structural behavior and elastic properties of alkaline earth tellurides (AETe; AE = Ca, Sr, Ba) by using two body interionic potential approach with modified ionic charge (Z _m e). This method has been found quite satisfactory in case of the rare earth compounds. The equation of state curve, structural phase transition pressure from NaCl (B1) to CsCl (B2) phase and associated volume collapse at transition pressure of alkaline earth tellurides (AETe) obtained from this approach, so have been compared with experimentally measured data reveal good agreement. We have also investigated bulk modulus, second and third order elastic constants and pressure derivatives of second order elastic constants at ambient pressure which shows predominantly ionic nature of these compounds. First time, we have calculated the Poisson ratio, Young and Shear modulus of these compounds.      

High pressure studies of viscosity effects on isomerization

Abstract

The viscosity dependence of the isomerization process with comparatively low potential barrier was studied as a model of one-dimensional barrier crossing.

We found that the ground-state isomerization of DODCI fails to fit the Kramers equation. We analyzed this non-Kramers behavior by means of an approach of frequency dependent friction.     

CuO在高压下的状态方程、电学性质与相变

 在活塞－圆筒式高压装置上研究了CuO在4.5 GPa内的p-V关系，给出了它的状态方程、格临爱森参数γ₀、体积模量B₀以及B₀的压力导数B₀'。在金刚石压砧装置上，采用我们建立的电阻、电容测量方法研究了CuO在22 GPa内电阻、电容与压力的关系。实验结果表明，CuO的电阻和电容在一些压力下都发生了突然的变化。这些变化可能与CuO内部的电子结构和晶界处的结构状态变化有关。     

CdTe的状态方程及其高压相变

 用金刚石压砧高压X光衍射技术研究了Ⅱ-Ⅵ族化合物CdTe的室温状态方程和室温高压相变。实验的最高压力达39.2 GPa。实验中发现CdTe从(3.3±0.1)GPa开始从闪锌矿结构相相NaCl结构相转变，相变时体积收缩15.8%；从(10.3±0.2)GPa开始从NaCl相向β-Sn结构相转变，相变时无体积突变；在(12.2±0.2)GPa由β-Sn相向正交结构相转变，相变时也无体积突变。CdTe的压缩数据用最小二乘法以Bridgman状态方程和Murnaghan状态方程拟合，得到其零压时合相变压力时各个相的体弹模量及体弹模量的压力微商，并与其它的实验合理论结果进行比较。     

A Model Study of Equation of State of QCD at Finite Chemical Potential and Zero Temperature

In this paper, we give a direct method for calculating the partition function, and hence the equation of state （EOS） of QCD at finite chemical potential and zero temperature. In the EOS derived in this paper the pressure density is the sum of two terms： the first term P（μ）｜μ=0 （the pressure density at μ = 0） is a μ-independent constant; the second term, which is totally determined by G[μ] （p） （the dressed quark propagator at finite μ）, contains all the nontrivial μ-dependence. By applying a general result in the rainbow-ladder approximation of the Dyson-Schwinger approach obtained in our previous study [Phys. Rev. C 71 （2005） 015205], G[μ]（p） is calculated from the meromorphic quark propagator proposed in [Phys. Rev. D 67 （2003） 054019]. From this the full analytic expression of the EOS of QCD at finite μ and zero T is obtained （apart from the constant term P（μ）｜μ=0, which can in principle be caJculated from the CJT effective action）. A comparison between our EOS and the cold, perturbative EOS of QCD of Fraga, Pisarski and Schaffner-Bielich is made. It is expected that our EOS can provide a possible new approach for the study of neutron stars.     

Two-dimensional thermoelasticity solution for functionally graded thick beams

Two-dimensional thermoelasticity analysis of functionally graded thick beams is presented using the state space method coupled with the technique of differential quadrature. Material properties vary continuously and smoothly through the beam thickness, leading to variable coefficients in the state equation derived from the elasticity equations. Approximate laminate model is employed to translate the state equation into the one with constant coefficients in each layer. To avoid numerical instability, joint coupling matrices are introduced according to the continuity conditions at interfaces in the approximate model. The differential quadrature procedure is applied to discretizing the beam in the axial direction to make easy the treatment of arbitrary end conditions. A simply-supported beam with exponentially varying material properties is considered to validate the present method. Numerical examples are performed to investigate the influences of relative parameters.