Non-equilibrium electronic Grüneisen parameter

The electronic Grüneisen parameter, γ _e , is a fundamental parameter characterizing the relationship between thermal expansion and electronic specific heat. Conventionally, γ _e is measured at low temperatures for minimizing the lattice contribution to thermal expansion. In this paper, we extract γ _e by separating the electron and lattice contributions in time domain using ultrashort pulse excitation. We show that γ _e cannot be considered as a constant during the electron-lattice thermal nonequilibrium state. Instead, a revised expression for γ _e is proposed for the non-equilibrium electron–phonon system.     

Grüneisen关系式的简单推导

首先介绍了有关教科书中Gr櫣ｎｅｉｓｅｎ关系式的推导过程 ,然后给出了简单推导此关系式的方法 .     

Grüneisen parameters for layered crystals

The temperature dependences of Grüneisen parameters for layered crystals of the hexagonal crystal system are constructed. It is demonstrated that the Grüneisen parameters calculated in the framework of the model proposed by I.M. Lifshits for a strongly anisotropic crystal agree satisfactorily with those obtained from the experimental data for graphite, the most typical layered crystal. It is found that the effect of bending vibrations on the Grüneisen parameters decreases with a decrease in the anisotropy of the elastic properties.     

Chemical short-range-order effects on stability in δ-Pu–Ga alloys

We present results on the structural stability of Pu_{1? x} Ga _x alloys based on the local spin-density approximation and including non-local corrections to the exchange–correlation functional (generalized gradient approximation). First, we used both the linearized augmented plane-wave and the projector augmented wave (PAW) methods to calculate the energies of formation of five intermediate phases which occur in the Pu–Ga phase diagram. Then, PAW calculations were performed for various superstructures based on the fcc lattice to get the interaction parameters to describe the energetics of the δ-Pu–Ga solid solution. To discuss the effects of the chemical short-range order on the structural stability of the δ-Pu–Ga solid solution as a function of temperature, the cluster variation method configurational entropy has been introduced using the regular tetrahedron approximation. The solid part of the Pu-rich side of the phase diagram involving phase equilibria between the Pu phases, the δ-Pu–Ga solid solution and the Pu₃Ga compound is calculated. We show the importance of chemical short-range order on Ga solubility in δ-Pu.     

On determination of the Grüneisen parameter from experimental data

It is shown that the localization criterion for the crystal-liquid phase transition introduced earlier for macrostructures is also valid for nanocrystals. The variation of the parameters of activation processes (formation of vacancies and self-diffusion) with a decrease in the nanocrystal size is investigated. It is shown that the lattice of a nanocrystal is more perfect than that of a macrocrystal at low temperatures, while at high temperatures, the nanocrystal is activated by mobile vacancies to a greater extent than the macrocrystal.     

Melting and Grüneisen parameters of NaCl at high pressure

The Buckingham potential has been employed to simulate the melting and thermodynamic parameters of sodium chloride (NaCl) using the molecular dynamics (MD) method. The constant-volume heat capacity and Grüneisen parameters have been obtained in a wide range of temperatures. The calculated thermodynamic parameters are found to be in good agreement with the available experimental data. The NaCl melting simulations appear to validate the interpretation of superheating of the solid in the one-phase MD simulations. The melting curve of NaCl is compared with the experiments and other calculations at pressure 0－30GPa range.     

Grüneisen系数的统计物理学定义

将广义力对系统做功引起的能量(不含冷能)的相对变化ES/ES与广义坐标的相对变化y/y之比定义为微观Grüneisen系数γS,导出了计算Grüneisen系数统计平均值的微分方程.由该方程计算了人们熟悉的热力学系统的Grüneisen系数,结果与其他方法得到的结论完全一致.     

Measuring Grüneisen 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.     

Thermodynamics and surface properties of liquid Al–Ga and Al–Ge alloys

The surface properties of Al–Ga and Al–Ge liquid alloys have been theoretically investigated at a temperature of 1100 K and 1220 K respectively. For the Al–Ga system, the quasi chemical model for regular alloy and a model for phase segregating alloy systems were applied, while for the Al–Ge system the quasi chemical model for regular and compound forming binary alloys were applied. In the case of Al–Ga, the models for the regular alloys and that for the phase segregating alloys produced the same value of order energy and same values of thermodynamic and surface properties, while for the Al–Ge system, the model for the regular alloy reproduced better the thermodynamic properties of the alloy. The model for the compound forming systems showed a qualitative trend with the measured values of the thermodynamic properties of the Al–Ge alloy and suggests the presence of a weak complex of the form Al₂Ge₃. The surface concentrations for the alloys show that Ga manifests some level of surface segregation in Al–Ga liquid alloy while the surface concentration of Ge in Al–Ge liquid alloy showed a near Roultian behavior below 0.8 atomic fraction of Ge.     

Kondo entropy of δ-phase plutonium and its impact on Pu alloy phase diagrams

We present a new analysis of the heat capacity of δ-phase Pu-5 at.% Al with a fit using a single-ion Kondo term and a low-temperature Schottky anomaly in addition to the Debye and linear terms. The Kondo and Schottky terms together contribute 1.2 R to the entropy at 300?K. We show how the extra entropy could affect the alloy phase diagrams of δ-phase Pu.     

Anderson–Grüneisen parameter for lower mantle region of the Earth under adiabatic condition

A revised model of volume dependence of Anderson–Grüneisen parameter for lower mantle under adiabatic condition is presented in this study, and the volume dependence of (α T/C _P =α ′) is then discussed. It is shown that the results are in good agreement with seismic data of the Earth.     

Measurement of the electronic Grüneisen constant using femtosecond electron diffraction

We report the first accurate measurement of the electronic Grüneisen constant gamma(e) using a novel method employing the new technique of femtosecond electron diffraction. The contributions of the conduction electrons and the lattice to thermal expansion are differentiated in the time domain through transiently heating the electronic temperature well above that of the lattice with femtosecond optical pulses. By directly probing the associated thermal expansion dynamics in real time using femtosecond electron diffraction, we are able to separate the contributions of hot electrons from that of lattice heating, and make an accurate measurement of gamma(e) of aluminum at room temperature. This new approach opens the possibility of distinguishing electronic from magnetic contributions to thermal expansion in magnetic materials at low temperature.     

A physically-based Mie–Grüneisen equation of state to determine hot spot temperature distributions

A physically-based form of the Mie–Grüneisen equation of state (EOS) is derived for calculating 1d planar shock temperatures, as well as hot spot temperature distributions from heterogeneous impact simulations. This form utilises a multi-term Einstein oscillator model for specific heat, and is completely algebraic in terms of temperature, volume, an integrating factor, and the cold curve energy. Moreover, any empirical relation for the reference pressure and energy may be substituted into the equations via the use of a generalised reference function. The complete EOS is then applied to calculations of the Hugoniot temperature and simulation of hydrodynamic pore collapse using data for the secondary explosive, hexanitrostilbene (HNS). From these results, it is shown that the choice of EOS is even more significant for determining hot spot temperature distributions than planar shock states. The complete EOS is also compared to an alternative derivation assuming that specific heat is a function of temperature alone, i.e. c_v(T). Temperature discrepancies on the order of 100–600 K were observed corresponding to the shock pressures required to initiate HNS (near 10 GPa). Overall, the results of this work will improve confidence in temperature predictions. By adopting this EOS, future work may be able to assign physical meaning to other thermally sensitive constitutive model parameters necessary to predict the shock initiation and detonation of heterogeneous explosives.     

Modified Grüneisen relation for Cu and Ag

It is shown that the modified Grüneisen relation for the thermal expansion coefficient of cubic crystals depends on the isochoric Grüneisen parameter, its first-order isochoric derivative and the first-order isochoric derivative of the isothermal Grüneisen parameter. As an application of the present theory we have calculated these new anharmonic parameters and its effect on the thermal expansion coefficient of silver and copper.     

Grüneisen状态方程的数值解及其应用

从Grüneisen状态方程、冲击绝热关系出发,给出求解相关微分方程组的Runge-Kutta法格式.研究钨材料的内部压力、Grüneisen系数、冷压、冷能与比体积之间的数值关系,得出Grüneisen系数、冷压、冷能及常温下压力随比体积的变化曲线.计算给出的压力一比体积关系同实验数据符合较好.在此基础上给出两个压缩状态(比体积分别为V1,V2)下压力随温度变化的曲线,说明温度的变化对压力的影响小于比体积变化的影响.     

Grüneisen系数与铝的高温高压状态方程

基于Gray金属三相状态方程模型,分别采用ργ=常数,Gray,GRIZZLY的Grüneisen系数模型和从头算给出的Grüneisen系数,系统计算了铝的熔化曲线、等熵压缩线、等温压缩线和等熵卸载线,计算结果与实验数据比较表明;在冲击压力约为500GPa的宽广压力范围,GRIZZLY Grüneisen系数模型是最适合描述铝的热力学特性的形式,ργ=常数模型次之,在高压区,Gray和从头算的Grüneisen系数的计算结果与实验值差距较大. 关键词： Grneisen系数 状态方程 铝     

Concentration dependence of thermodynamic,transport and surface properties in Ag–Cu liquid alloys

Thermodynamic, transport and surface properties of Ag–Cu liquid alloys have been investigated on the basis of a simple statistical model. The free energy of mixing, heat of mixing and entropy of mixing have been computed to understand the thermodynamic properties of Ag–Cu alloys in liquid state at 1,423 K. The concentration–concentration fluctuations in the long wavelength limit and the chemical short range order parameter have been determined to comprehend the microscopic and structural information of the alloy. The viscosity and surface tension of the alloy have been evaluated to analyze the transport and surface properties. The theoretical analysis reveals that the energy parameter is temperature dependent, and that Ag–Cu liquid alloy is a weakly interacting-phase separating system.     

Effects of intrinsic anharmonicity in the Mie–Grüneisen equation of state and higher order corrections

The usual quasiharmonic Mie–Grüneisen (MG) equation of state is modified by the inclusion of ‘intrinsic anharmonicities’, which have been considered up to now primarily in the high temperature limit. A comparison with experimental data for the rare gas solids, Ar, Kr and Xe and for MgO reveals that the anharmonic contributions cannot be represented perfectly within the MG approximation. A small but significant modification of the MG approach is presented to estimate intrinsic anharmonic contributions within a mean-field approximation for the thermal part of the internal energy. This estimate results in reasonable interpolations to low temperatures, where quantum effects are dominant. The present approach is also compared with more restricted recent theoretical results.