Generalized Grüneisen parameters and low temperature limit of lattice thermal expansion of cadmium and zirconium

The generalized Grüneisen parameters (γ′ _j ) and (γ″ _j ) for cadmium and zirconium were calculated from the second- and third-order elastic constants to determine the low temperature limit of the volume thermal expansion of these metals of hexagonal symmetry. The low temperature limit of cadmium and zirconium was calculated to be positive values indicating a positive volume expansion down to 0 K even though many Grüneisen gammas were found to be negative.     

Coupled temperature dependences of volume and compressibility

We present a new method for understanding the changes with temperature of the volume and compressibility of solids. These changes depend on five parameters: V ₀, B ₀, Θ, γ _G and δ _T. V ₀ and B ₀ are the atomic volume and bulk modulus at T?=?0?K, Θ is the Debye temperature, γ _G is the Grüneisen parameter, and δ _T is the Anderson–Grüneisen parameter. Equations for the temperature-dependent volume, bulk modulus and thermal expansion are given, and examples of the use of these equations are provided, with particular emphasis on the light actinides. For the elements, we examine the relationship between experimental values of γ _G and δ _T, and find no clear correlation. In particular, Swenson's rule, which states that the bulk modulus does not change with temperature if the volume is held constant, is a poor approximation to the data. We reveal a new useful approximate relationship between dB/dP and γ _G. We find that the thermodynamic quantity q, which describes the variation in γ _G with volume, distributes around 2, not around 1, as often assumed. We show that the thermal- expansion behavior of Si and Ge (including negative thermal expansion at low temperatures) are well described with the use of a two-level invar model.     

Interatomic forces,Grüneisen and Anderson-Grüneisen parameters of ionic crystals

The general expression for the Anderson-Grüneisen parameterδ recently derived by Gupta and others, has been used to study the variation ofδ with the Grüneisen parameterγ employing the interaction approach. For this purpose four potential energy functions have been selected. It is found thatδ values evaluated by the modified Varshni-Shukla potential are better than other forms of overlap repulsive interaction. The variation ofδ withγ is also studied by plotting curves betweenδ andγ. The method of least-squares has been employed to yield the best fitted equation.     

高压下铝的Grüneisen参数的实验测量

 采取突然加压的方法，测量在施压过程中产生的温度变化，从而直接决定物质的格留乃森（Grüneisen）参数。第一次在固体传压介质中进行该种实验，并在高达3.5 GPa的压力范围内，直接测量了铝的格留乃森参数随压力的变化。     

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     

Mechanical properties,lattice thermal conductivity,infrared and Raman spectrum of the fullerite C24

Lightweight carbon materials with excellent thermal and mechanical properties have important applications in aerospace industry. In this study, the stability, mechanical properties, lattice thermal conductivity, electronic structure, infrared and Raman spectrum of sp³ hybridized low-density fullerite C₂₄ were investigated according to density functional theory (DFT) calculations. It was found that the fullerite C₂₄ was both thermodynamic and dynamic stable. Quasi-harmonic approximation and Grüneisen parameter calculations clarified why the fullerite C₂₄ had a positive thermal expansion coefficient at low temperature. The fullerite C₂₄ also exhibited excellent mechanical properties. Interestingly, the Vickers hardness of carbon allotropes was found to almost be linear proportional to the density of a carbon material. HSE06 electronic structure calculations showed that it was a semiconductor with direct bandgap of 2.56 eV. Anharmonic lattice dynamic calculations showed that its thermal conductivity was higher than semiconductor silicon. Besides, Raman and infrared active modes as well as the corresponding spectra were presented.     

KH2PO4和(CH3NHCH2COOH)CaCl2在高压下的状态方程与相变

 在活塞圆筒式p-V关系测量装置上，研究了KH₂PO₄（KDP）和(CH₃NHCH₂COOH)CaCl₂［Tris-sarcosine calcium chloride（TSCC）］在室温下、4.5 GPa内的p-V关系。实验结果表明：KDP在2.1 GPa左右有一个相变；TSCC在0.8 GPa和3.2 GPa左右各有一个相变。本工作还给出了它们在相变前后的状态方程，以及它们的格临爱森参数γ₀、体积模量B₀和B₀的压力导数B₀'。     

石墨烯低温热膨胀和声子弛豫时间随温度的变化规律

考虑到原子非简谐振动和电子-声子相互作用,用固体物理理论和方法研究了石墨烯格林艾森参量和低温热膨胀系数以及声子弛豫时间随温度的变化规律,探讨了原子非简谐振动项对它们的影响.结果表明:1)在低于室温的温度范围内,石墨烯的热膨胀系数为负值,随着温度的升高,其热膨胀系数的绝对值单调增加,室温热膨胀系数为-3.64×10~(-6)K~(-1);2)简谐近似下的格林艾森参量为零.考虑到非简谐项后,格林艾森参量在1.40-1.42之间并随温度升高而缓慢增大,几乎成线性关系,第二非简谐项对格林艾森参量的影响小于第一非简谐项;3)石墨烯声子弛豫时间随着温度的升高而减小,其中,温度很低(T10 K)时变化很快,此后变化很慢,当温度不太低(T300 K)时,声子弛豫时间与温度几乎成反比关系.     

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.     

室温下金属中电子格林艾森常数的测量

在室温条件下用自己研制的超快电子衍射实验设备精确测量了金属铝的电子格林艾森常数(γ_e).当飞秒脉冲激光瞬间加热铝膜时,电子和晶格对固体热膨胀的作用在时间域上是不同步的,借助于超快电子衍射实验设备的高时间分辨能力,可以摆脱以往测量非磁性金属材料时低温的限制,在室温条件下,实验通过直接观测瞬间加热的铝膜中电子和晶格对热膨胀的不同贡献得到电子的格林艾森常数. 关键词： 格林艾森常数 超快电子衍射 晶格热运动 电子热运动     

Similarity criteria for Debye temperatures of simple solids at compression

A similarity criterion for the volume dependence of Debye temperatures of simple solids at compression is presented. It is shown that the volume dependences of the characteristic Debye temperatures of various solids fall on a single common curve in dimensionless coordinates. The validity of the model is tested on examples of solids with various types of interatomic forces – molecular crystal, ionic crystal, metals and covalent crystal.     

KBrO3在高压下拉曼光谱和结构的研究

利用原位高压拉曼散射和X射线衍射技术,研究了KBrO3在高压下晶格振动和晶体结构演化行为.最高压力达30.9 GPa.通过拉曼光谱发现,在高压下拉曼峰位除了单调移动,没有其它变化,表明KBrO3在研究的压力范围没有发生相变.原位高压X射线衍射实验数据显示,其在高压下依然保持常压的六方结构.通过进一步分析,分别得到了体弹模量B0=25.9(2) GPa(B′0=5.68(0.38))和部分拉曼峰的Grüneisen参数.     

Grüneisen parameter for HCP iron at extreme compression

The Thomas–Fermi approximation gives the Grüneisen parameter γ=γ_∞=1/2 for all materials at extreme compression (P→∞ or V→0). After re-analyzing the existing experimental data of volume dependence of Grüneisen parameter γ of hexagonal close-packed (HCP) iron, we find that γ=1/2+a(V/V ₀)^1/3+b(V/V ₀) ⁿ , where a, b and n are constants. Based on this new form of γ, the second Grüneisen parameter q, the Debye temperature θ_D and the shear sound velocity v _s of HCP iron are discussed in the present work. It is found that the zero pressure second Grüneisen parameter q ₀=0.654, which is consistent with the previously determined value of HCP iron for Earth's core physics from Dubrovinsky et al. The calculations for the Debye temperature and the shear sound velocity are also found to be in good agreement with the experimental data.     

New constraints on gruneisen parameters applications to equations of state for pressure markers

Abstract

“Regular” linear relations between shock and particle velocities, u_s = u_s0, + c · u_p, imply a divergence of the Hugoniot pressure p_H at a critical compression V _c/V _o = (c-1)/c, where the thermal pressure Δp _th = (γ/V)· ΔU _th = p _H-p _T becomes very large with respect to the cold (isothermal) pressure p _T at this compression. The Hugoniot relation for the total internal energy U _H results in this case in the relation γ_c = 2(c- 1) for the Grüneisen parameter in this region. Experimental data for the zero pressure value Γ_o and its derivative Γ_o together with theoretical data for the limiting value γ_∞ = 2/3, and the additional expenmental value γ_c are then used to determine the thermal (phonon) pressure with the common Mie-Grüneisen assumption.     

Liquid fluorine properties by the hardsphere model with attractive interactions

We test the validity of an approximate equation of state of real fluids and the expression for surface tension of hardsphere liquids with attractive interactions derived by Sharma and others by obtaining expressions for isothermal compressibility,C ₁-parameter and acoustical parameter and relate them to microscopic Grüneisen parameter. The calculated values for liquid fluorine show fair agreement with experimental values.     

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.     

Volume variation of nuclear Grüneisen parameter for equation of state studies

The method of first principle pseudopotential is used to simulate the volume variation of nuclear Grüneisen parameter. The elements Al and Be, for which Neal’s experimental data exist are investigated. The nuclear Grüneisen obtained from the details of phonon frequencies are in better agreement with the experimental data as compared to those obtained from approximate Slater and Dugdale-MacDonald methods, often used in shock wave studies.     

Theoretical results concerning the influence of non‐random‐field defects

We shall focus on extended defect systems and review their critical behavior. Primarily, with two aims, one of which is to understand phase transitions and how to derive effective dimension of extended defects with various structures, and the other is to propose a new research-method for defect systems, we let extended defects grow on a triangular lattice with frustration in a similar fashion to diffusion-limited aggregation, and discuss the situation. The existence of phase transitions, phase diagram, effective defect dimension, etc. will be shown. Furthermore, we shall summarize theoretical studies of extended defect systems on phase diagrams, critical behavior, tricritical behavior, and crossover behavior as static properties, and on nonconserved systems and conserved systems as dynamic properties.