共查询到20条相似文献,搜索用时 15 毫秒
1.
We employ a first-principles plane wave method with the
relativistic analytic pseudopotential of Hartwigsen, Goedecker and Hutter
(HGH) scheme in the frame of DFT to calculate
the equilibrium lattice parameters and the thermodynamic properties of
AlB2 compound with hcp structure. The obtained lattice parameters are in
good agreement with the available experimental data and those calculated by
others. Through the quasi-harmonic Debye model, obtained successfully are
the dependences of the
normalized lattice parameters a/a0 and c/c0 on pressure P, the normalized
primitive cell volume V/V0 on pressure P, the variation of the thermal
expansion α with pressure P and temperature T, as well as the Debye
temperature \ThetaD and the heat capacity CV on pressure P and
temperature T. 相似文献
2.
The transition phase of GaAs from the zincblende (ZB)
structure to the rocksalt (RS) structure is investigated by ab initio plane-wave
pseudopotential density functional theory method, and the thermodynamic
properties of the ZB and RS structures are obtained through the
quasi-harmonic Debye model. It is found that the transition from the ZB
structure to the RS structure occurs at the pressure of about 16.3\,GPa,
this fact is well consistent with the experimental data and other theoretical results. The
dependences of the relative volume V/V0 on the pressure P, the Debye
temperature \Th and specific heat CV on the pressure P, as well as
the specific heat CV on the temperature T are also obtained
successfully. 相似文献
3.
本文报导了在流体静压力18000kg/cm2的范围内,锗隧道二极管伏安特性随压力变化的实验结果。测量了十六只锗隧道二极管的峯值电流IP、峯值电压VP、谷值电流IV、谷值电压VV、指数过剩电流IX和反向隧道电流等参数与流体静压力的关系。结果表明:峯值电流IP相对于压力的半对数作图为斜率不同的二段下降直线,在5000—9000kg/cm2范围内有转折点;峯值电压随压力改变较小;在误差范围内谷值电压不随压力而改变。对于大部分被测管子,谷值电流与压力的关系类似于峯值电流与压力的关系;随着压力的增加,指数过剩电流区向高偏压方向移动。讨论了峯值电流及指数过剩电流随压力变化的规律和其他结果。认为转折点的存在是表明隧道跃迁机构的改变;由指数过剩电流区固定电流值测偏压随压力改变,求得禁带宽度的压力系数与其他方法获得的结果很好符合。 相似文献
4.
First-principles calculations of structural and thermodynamic properties of BeB2 compound 总被引:1,自引:0,他引:1 下载免费PDF全文
The lattice parameter bulk modulus and pressure derivative of BeB2 are calculated by using the Cambridge Serial Total Energy Package (CASTEP) program in the frame of density function theory. The calculated results agree well with the average experimental data and other theoretical results. Through the quasi-harmonic Debye model, the dependences of the normalized lattice parameters a/ao, c/c0 and the normalized primitive cell volume V/Vo on pressure P, the variation of the thermal expansion coefficient ~ with pressure P and temperature T, as well as the dependences of the heat capacity Cv on pressure P and temperature T are obtained systematically. 相似文献
5.
The transition phase of GaN from zincblende (ZB) structure to rocksalt structure (RS) is investigated by ab initio plane-wave pseudopotential density functional theory method, and the thermodynamic properties of the ZB and RS structures are obtained through the quasi-harmonic Debye model. We find that the transition phase from the ZB structure to the RS structure occurs at the pressure of 42.2 GPa, which is in good agreement with other calculated values. Moreover, the dependences of the relative volume V/V0 on the pressure P, the Debye temperature Θ and heat capacity CV on the pressure P, as well as the heat capacity CV on the temperature T are also successfully obtained. 相似文献
6.
The transition phase of PtN from zincblende (ZB) structure to rocksalt (RS) structure is investigated by ab initio plane-wave pseudopotential density functional theory method, and the thermodynamic properties of the ZB and RS structures under high pressure and temperature are obtained through the quasi-harmonic Debye model. The transition phase from the ZB structure to the RS structure occurs at the pressure of 18.2 GPa, which agrees well with other calculated values. Moreover, the dependences of the relative volume V/V0 on the pressure P, the Debye temperature Θ and heat capacity CV on the pressure P, together with the heat capacity CV on the temperature T are also successfully obtained. 相似文献
7.
The present paper addresses the pressure-induced structural aspects of ZnS-type (B3) to NaCl-type (B1) structure in AlY (Y=N, P, As). An effective-interionic interaction potential (EIoIP) with long-range Coulomb and three-body interactions and the Hafemeister-and-Flygare-type short-range overlap repulsion extended up to the second-neighbour ions and the van der Waals (vdW) interaction is developed. Emphasis has been given on evaluating the vdW coefficients by the Slater-Kirkwood variational method, as both the ions are polarizable. The lattice model calculations have revealed reasonably good agreement with the available experimental data on the phase-transition pressures (Pt=16, 14, 7.5 GPa) and the elastic properties of AlY (Y=N, P, As). The equation of state curves (plotted between V(P)/V(0) and pressure) for both the B3 and B1 structures obtained are in fairly good agreement with the experimental results. The calculated values of the volume collapses [ΔV(P)/V(0)] are also close to their observed data. Further, the variations of the second-order elastic constants with pressure follow a systematic trend that is almost identical to that exhibited by the observed data measured for other semiconducting compounds with B3→B1 structural phase transitions. 相似文献
8.
H. Neubauer 《Zeitschrift für Physik A Hadrons and Nuclei》1969,226(3):211-221
An apparatus for production of hydrostatic pressure is described using a mixture of n-pentane and iso-pentane, which transmits pressure uniformly still at low temperatures. The superconductive transitions of the A 15(β- W type)-compounds Nb3Sn, Nb3Al, V3Si and the B 1(NaCl type)-compound NbN have been measured under pressure up to 18 · 103 kp/cm2. The transition temperatures of the compounds V3Si and NbN are increasing with pressure. Further measurements have been done on some selected ternary compounds, e.g. Nb3(Al1?x Ge x ), to prove some predictions for the effect of pressure on superconductive transition. 相似文献
9.
10.
利用基于密度泛函理论的第一性原理平面波赝势方法 并结合准谐徳拜模型研究了NaCl结构的TiC在高压下的弹性性质、电子结构和热力学性质. 计算所得零温零压下的晶格常数、体弹模量及弹性常数与实验值符合得很好. 零温下弹性常数和弹性模量随压强增大而增大. 通过态密度和电荷密度的分析, Ti-C键随压强增大而增强. 运用准谐德拜模型, 成功计算了TiC在高温高压下的体弹模量、熵、热膨胀系数、徳拜温度、 Grüneisen参数和比热容. 结果表明压强对体弹模量、热膨胀系数和徳拜温度的影响大于温度对其的影响. 热容随着压强升高而减小, 在高温高压下, 热容接近Dulong-Petit极限. 相似文献
11.
Abstract Initial rates of hydrolysis of maltose and maltotriose over an immobilized glucoamylase have been measured up to 127 MPa at 25±0.1°C. The observed rates have been analyzed showing the reaction pathways of both hydrolyses to be E+S?ES*?ES7ast;E+P, where E, S, P, ES*, and ES denote the enzyme, the substrate, the product, a substrate-subsite complex, and a substrate-active site complex, respectively. The apparent maximum rate rmand the apparent Michaelis constant Km as well as their respective pressure dependences in terms of the apparent activation volume Δ Vapp # and the apparent volume of reaction Δ Vapp have been evaluated. Small absolute values of Δ Vapp num; and Δ Vapp for both reactions have been discussed on the basis of the reaction mechanism. 相似文献
12.
Ke Liu Duan-Wei He Xiao-Lin Zhou Hai-Hua Chen 《Physica B: Condensed Matter》2011,406(15-16):3065-3069
We employ the first-principles plane wave pseudopotential density functional theory method to calculate the equilibrium lattice parameters of osmium and the thermodynamic properties of hcp structure osmium. The obtained lattice parameters are in good agreement with the experimental data investigated up to 58.2 GPa using radial X-ray diffraction (RXRD) together with lattice strain theory in a diamond-anvil cell and the available theoretical data of others. Through the quasi-harmonic Debye model, the dependencies of the normalized lattice parameters a/a0 and c/c0 on pressure P, the normalized primitive volume V/V0 on pressure P, the Debye temperature ΘD and the heat capacity CV on pressure P and temperature T, as well as the variation of the thermal expansion α with temperature and pressure are obtained successfully. 相似文献
13.
An effective interionic interaction potential is developed to discuss the pressure induced structural phase transformation and mechanical properties of InX (X = N, P, As) semiconducting compounds. The effective interionic potential consists of the long-range Coulomb and three-body interactions and the Hafemeister and Flygare type short-range overlap repulsion extended upto the second neighbour ions and the van der Waals interaction. The present calculations have revealed reasonably good agreement with the available experimental data on the phase transition pressures (Pt = 11.5, 10, 7.5 GPa) and the elastic properties of InX (X = N, P, As). The equation of state curves (plotted between V (P)/V(0) and pressure) for both the structures zincblende (B3) and rocksalt (B1) structures obtained by us are in fairly good agreement with the experimental results. The calculated values of the volume collapses [ΔV(P)/V(0)] are also closer to their observed data. 相似文献
14.
Sung Il Jeon Jung Hoon Park Edoardo MagnoneYong Taek Lee Eric Fleury 《Current Applied Physics》2012,12(2):394-400
The hydrogen permeation characteristics of alloy membranes based on Pd-coated V90Al10 alloy membrane have been investigated in the pressure range 1-3 atm under pure hydrogen and hydrogen-carbon dioxide gas mixture at 450 °C. Hydrogen permeation experiments have been confirmed that hydrogen flux was 21.1 ml/min/cm2 for a Pd-coated V90Al10 alloy membrane (thickness: 0.5 mm) using pure hydrogen as the feed gas. It has been found that Pd-coated V90Al10 alloy membranes exhibit good resistance to hydrogen embrittlement in pure hydrogen atmosphere. After different hydrogen permeation flux tests under different pressure condition in presence of hydrogen-carbon dioxide gas mixture, the characteristics of the Pd-coated V90Al10 alloy membranes were examined by ex-situ analysis techniques. The loss of cell performance observed in the presence of hydrogen-carbon dioxide gas mixture is mainly attributed to both physical and chemical degradations of membrane, which led to structural changes in the Pd-coated V90Al10 alloy membrane. 相似文献
15.
Jae Hong Kim Hee Suk Jung Chung Hee Park Tae Jin Kang 《Journal of Physics and Chemistry of Solids》2014
Flexible quasi-solid-state dye-sensitized solar cells (DSSCs) with porous poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP)/polyethylene oxide-co-polypropylene oxide-co-polyethylene oxide (P123) electrolyte membranes were fabricated and their photocurrent–voltage (I–V) characteristics are studied. Flexible TiO2 photoelectrodes were prepared using the compression method and porous PVdF-HFP/P123 membranes, by the nonsolvent-induced phase inversion technique. To activate the electrolyte membrane, the membrane was immersed in liquid-state electrolyte. Increased compression pressure improved the interconnection between TiO2 nanoparticles, enhancing the photovoltaic performances of the flexible liquid-state DSSCs to a maximum of 3.92% efficiency. Meanwhile, the overall pore structure of the PVdF-HFP/P123 membranes was controlled by varying the blend ratio of P123 to PVdF-HFP. Membranes higher in P123 content gave larger pores and pore volume, increasing the electrolyte uptake of the porous membrane, and thus the ionic conductivity of the electrolyte membrane as well. The photovoltaic characteristics of the flexible quasi-solid-state DSSCs containing a porous PVdF-HFP/P123 electrolyte membrane showed a maximum at 50 wt% P123 content, which gave a short-circuit current density (Jsc) value of 7.28 mA/cm2, an open-circuit voltage (Voc) of 0.67 V, a fill factor (FF) of 0.61 and an energy conversion efficiency (η) of 2.98%. Furthermore, the device designed in this study showed good durability compared to those based on liquid-state electrolyte. 相似文献
16.
The structural, elastic, and electronic properties of SrZrN2 under pressure up to 100?GPa have been carried out with first-principles calculations based on density functional theory. The calculated lattice parameters at 0?GPa and 0?K by using the GGA-PW91-ultrasoft method are in good agreement with the available experimental data and other previous theoretical calculations. The pressure dependence of the elastic constants and the elastic-dependent properties of SrZrN2, such as bulk modulus B, shear modulus G, Young's modulus E, Debye temperature Θ, shear and longitudinal wave velocity VS and VL, are also successfully obtained. It is found that all elastic constants increase monotonically with pressure. When the pressure increases up to 140?GPa, the obtained elastic constants do not satisfy the mechanical stability criteria and a phase transition might has occurred. Moreover, the anisotropy of the directional-dependent Young's modulus and the linear compressibility under different pressures are analysed for the first time. Finally, the pressure dependence of the total and partial densities of states and the bonding property of SrZrN2 are also investigated. 相似文献
17.
18.
M. N. Magomedov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2013,7(4):697-706
The dependences of the specific surface energy (σ) and its isochoric temperature derivative (?σ/?T) V on the degree of compression (V/V 0) of the crystal are calculated on the basis of the Mie-Lennard-Jones pair potential of interatomic interaction. The calculations are performed for all face-centered cubic crystals of inert gases (from Ne to Rn) to the degree of compression V/V 0 = 0.016 along three isotherms: 1K, T m and 300 K, where T m is the melting temperature at zero pressure (V/V 0 = 1). The activation processes such as the creation of vacancies and self-diffusion are taken into account in the calculations. It is shown that the isotherm σ(V/V 0) reaching its maximum at (V/V 0)max sharply decreases upon further compression. The surface energy becomes negative (σ(V/V 0) fr =0) at V/V 0 ≤ (V/V 0) fr < (V/V 0)max which should stimulate the process of crystal fragmentation, i.e., an increase in the specific (per atom) intercrystallite surface. It is shown that at high temperatures the condition of fragmentation holds in the crystal in the case of uniform tension, but it is already in the region of the liquid phase. The values of σ, (?σ/?T) V , the vacancy concentration and the fraction of the diffusion atoms are estimated at the points: V/V 0 = 1, (V/V 0)max and (V/V 0) fr at 1 K, Tm and 300 K. The size evolution of the surface and activation parameters is studied using neon as an example. 相似文献
19.
利用基于密度泛函理论的全势能线性糕模轨函法研究了闪锌矿(B3),NiAs(B8)和岩盐(B1)结构的AlAs的相变、结构性质以及热动力学性质.对B3-B8和B3-B1结构的能量体积曲线做公切线,得到了B3→B8相变压力为5.44 GPa,并预测到B3→B1相变压力为6.46 GPa.同时计算了高压下B8相的结构性质,结果显示当V/V0≈0.7—1.05时,c/a基本保持恒定(仅有约 0.2%的波动);当V/V0≈0.4—0.7,c/a随着V/V0的减小而近似线性地增大.通过状态方程拟合,得到了AlAs的相对体积V/V0与压强P的函数关系,B8相的状态方程与实验结果符合很好.最后利用准谐德拜模型得到了AlAs的体弹模量B随压力P的变化关系以及不同压强下热容CV与温度T的关系.
关键词:
相变
热力学性质
第一性原理 相似文献
20.
A.S. Kaminskii 《Solid State Communications》2004,130(11):723-727
A phenomenological kinetic equation is proposed to describe a process of a hexavacancy (V6) orientation in silicon samples. The orientation kinetics of V6 was investigated under a uniaxial compressional stress along the [111] axis of the crystal. Parameters appeared in the matrix equation of the orientation kinetics of V6 as functions of pressure and annealing temperature were obtained and their values were estimated. In the case of the inequivalent V6 centers, the pressure dependence of the difference in the magnitude of their binding energies was determined. 相似文献