共查询到20条相似文献,搜索用时 78 毫秒
1.
用一种非简谐晶格动力学方法, 使用相互作用势作为惟一的输入参数, 准确地计算了固体氩的各个声子的频率和弛豫时间. 并将这些结果进一步和玻尔兹曼输运方程相结合, 预测了固体氩从10 K 到80 K 区间的热导率, 并得到了与实验值非常符合的结果. 分析了运用非简谐晶格动力学方法进行数值计算过程中的各个相关的计算参数, 包括布里渊区中倒格子矢量的选取, δ 函数的展宽的选择等对热导率和声子弛豫时间预测结果的影响. 通过对各个声子模式对热导率贡献的分析, 发现随着温度升高, 高频声子对于热导率的贡献率也逐渐变大, 结果和理论预测完全一致.
关键词:
热导率
固体氩
非简谐晶格动力学
声子 相似文献
2.
非简谐效应是诸如软模相变、负热膨胀、多铁性和超低热导率等材料性质的根源.已有的关于量化材料非简谐性的方法没有给出清晰准确的非简谐性描述符,并且计算流程复杂,需要极其耗时的分子动力学模拟.故亟需提出一个可以快速计算的非简谐性描述符,用来理解、评估、设计和筛选具有强非简谐性的功能材料.本研究将晶格非谐性分解为单声子非谐性σ((q,j))A,并提出温度依赖的晶格非谐性的定量描述符Aph(T).该描述符既可以定量描述从Si,GaAs,CdTe,NaCl到CsPbI3的晶格非谐性的变化趋势,又可以成功预测非简谐效应驱动的体积模量和晶格热导率性质的变化.本工作提出的非简谐性描述符能够快速量化材料非简谐性,并且可直观地展现材料非简谐效应的声子模态分布.本方法计算简单、高效且有效,可为基于非简谐性筛选与设计材料打下基础. 相似文献
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将重费米子超导体看成由s电子和f电子组成的系统,得到了一种可能的低能元激发模——超声Plasmon。证明在一定条件下,电子间通过交换这种低能集体元激发模,除了可导致s电子形成Cooper对外,同时还可导致s-f电子间混合对的形成。对系统的介电函数作了RPA近似计算,得到了超导转变温度的表达式,并讨论了混合对效应。另外,通过对比热反常的分析,讨论了在重费米子超导体中存在超声Plasmon模的可能性。 相似文献
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本文修改了Landshoff-Nachtmann的软玻密子(Pomeron P)场论模型.从强子组分夸克具有结构的观点出发,根据高能强作用软过程中的最大非微扰强作用反应假定,提出了有关软P新的结构图像.对撞强子中的一对组分夸克被分解为裸夸克和一系列非微扰胶子(和夸克对).与此相应,软P的结构是由胶子形成的一系列切割梯形图之和所代表.在系统能量s很大而动量转移|t|很小的多重雷吉(Regge)运动学区间,并在保留lns的领头阶近似下,计算了这组切割梯形图之和所对应的散射振幅和总截面.它们的表达式出现了对s的Regge型幂次因子,得出了软P轨迹的简洁表达式.简单说明了按本文提出的方案可以讨论那些相关的强作用过程. 相似文献
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对晶粒尺寸为194,86和56nm的纳米晶锐钛矿相TiO2,进行了从83到723K的变温拉曼散射测量,并对Eg(1)模式进行了详细研究.根据非简谐效应和声子局域模型,对Eg(1)拉曼峰进行了拟合与计算.结果表明,以上三种纳米晶粒的晶格振动机理,在本质上是相同的.三声子过程对频率蓝移起主要作用.为了得到很好的拟合,需要同时考虑三声子和四声子过程.随着温度的升高,四声子过程增强,并对三声子过程起抵消作用.与非简谐衰减相关的声子寿命随着晶粒
关键词:
2')" href="#">纳米晶TiO2
拉曼散射
非简谐耦合
声子局域 相似文献
11.
Solitons are simulated in an anharmonic linear lattice that is susceptible to a soft mode instability. The soft mode characteristic
is introduced in the system by the addition of a term (−Au
n
2
) in the potential between the neighbouring atoms and the evolution of the system is studied as the soft mode parameterA varies from zero to the square of the limiting optical frequency. It is shown that the displacement pattern of the system
shows three regions. First there is a region in which the relative displacements of the atoms show large amplitude oscillations.
This is followed successively by a domain in which the relative displacements of the atoms are negligible and then by the
soliton itself. In the soft mode region, the displacements of the atoms preceding the soliton decrease drastically in a linear
fashion first, parabolically next and later become steady. It further exhibits a kind of devil’s stair cases. 相似文献
12.
The behaviour of the impurity modes due to a pair of substitutional impurities characterized by both mass as well as force-constant
changes and occupying nearest neighbour positions in a diatomic linear chain, is studied. The results are compared with those
for the case of impurity pairs occupying next nearest neighbour sites discussed earlier as well as the existing three dimensional
calculations of Elliott and Pfeuty. The nearest neighbour impurity pair gap and local modes can be interpreted in terms of
two single impurities substituted in the two different sublattices unlike the next nearest neighbour pair modes. The inband
resonant modes are totally new features characteristic of the pair. Finally, the predictions of the theory are compared with
the available experimental data for Si-impurity-pair-complexes and qualitative agreement is shown. 相似文献
13.
A. Bulou A. Gibaud M. Debieche J. Nouet B. Hennion D. Petitgrand 《Phase Transitions》2013,86(1-4):47-53
Abstract The structural phase transition observed at ?13°C in KAlF4 is shown to be martensitic. The results of an investigation of the phonon spectrum by inelastic neutron scattering are reported. It is shown that the transition is preceded by the softening of a flat phonon branch. A model is proposed to explain how such a softening is related to the martensitic transition. 相似文献
14.
The concentration dependence of the reststrahl absorption in various mixed crystals exhibiting one, two and mixed mode behaviour
is investigated using the coherent potential approximation (cpa). The phonon Green’s function, the impurity mode frequencies and the strength of absorption are calculated in the Einstein
model from the generalizedcpa proposed by Tripathi and Behera which takes into account both mass and force constant changes. The introduction of a phenomenological
concentration dependence of the force constant change parameter is shown to provide a satisfactory explanation of the concentration
dependence of the experimental data for the twenty mixed crystal systems analysed. It is conjectured that the nearest neighbour
force constant of an impurity atom substituted at a host site is very much different from that of a perfect crystal consisting
of these impurity atoms and that both these play an important role in determining the one, two and mixed mode behaviour of
the mixed crystals. 相似文献
15.
G.H. Zhou Q.L. Xia J.R. Yan 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(2):207-213
Moving nonlinear localized vibrational modes (i.e. discrete breathers) for the one-dimensional homogenous lattice with quartic anharmonicity are obtained analytically by means
of a semidiscrete approximation plus an integration. In addition to the pulse-envelope type of moving modes which have been
found previously both analytically and numerically, we find that a kink-envelope type of moving mode which has not been reported
before can also exist for such a lattice system. The two types of modes in both right- and left-moving form can occur with
different carrier wavevectors and frequencies in separate parts of the plane. Numerical simulations are performed and their results are in good agreement with the analytical predictions.
Received 13 October 1999 and Received in final form 15 May 2000 相似文献
16.
G.H. Zhou Q.L. Xia J.R. Yan 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(3):297-304
The nonlinear localized vibrational modes of a one-dimensional atomic chain with two periodically alternating masses and force
constants are analytically investigated using a discrete multiple-scale expansion method. This model simulates a row of atoms
in the <1 1 1>-direction of sphalerite, or zinc blende, crystals. Owing to the structural asymmetry, the vibrational amplitude
is governed by a perturbed nonlinear Schr?dinger equation instead of the standard one found in one-dimensional lattices with
two alternating masses but uniform force constant. Although the stationary localized modes with carrier wavevector at the
Brillouin-zone boundary are similar to those of ionic lattices, the moving localized modes with wavevectors within the zone
are different owing to the perturbation. The calculation shows that the height of the moving localized modes in this lattice
dampens with time.
Received 14 May 2001 and Received in final form 12 July 2001 相似文献
17.
K S Viswanathan 《Pramana》1977,8(5):417-419
It is suggested that anomalous neutron scattering could prove a powerful experimental tool in studying ferroelectric phase
transition, the sublattice displacements of the soft modes as well as their symmetry characteristics. 相似文献
18.
In this paper, a model that combines the lattice Boltzmann method with the singularity distribution method is proposed to simulate a self-propelled particle swimming(exhibiting translation and rotation) in a channel flow. The results show that the velocity distribution for a self-propelled particle swimming deviates from a Maxwellian distribution and exhibits highvelocity tails. The influence of an eccentric potential doublet on the translation velocity of the particle is significant. The velocity decay process can be described using a double exponential model form. No large differences in the velocity distribution were observed for different translation Reynolds numbers, rotation Reynolds numbers, or regular intervals. 相似文献
19.
Marvin Bishop 《Journal of statistical physics》1982,29(3):623-629
The density fluctuations of one-dimensional Lennard-Jones systems are investigated by molecular dynamics simulation. The full Lennard-Jones potential is compared to the repulsive Lennard-Jones potential. It is found that the behavior of the density fluctuations at small wave vectors is determined by the repulsive portion of the potential. The variation of the fluctuations with density is explained. It is shown that these systems do not display hydrodynamics. 相似文献
20.
Lucovsky, Brodsky, Burstein (LBB) have studied the behaviour of mixed crystals by setting up a criterion for the existence
of local mode frequencies in real crystals starting from a diatomic linear chain model. This, while successfully predicting
the one and two mode behaviour for some systems fails to predict the mixed mode behaviour. We propose a similar criterion
for the existence of gap modes, by demanding that the gap mode predicted by the diatomic linear chain model should lie within
the gap of the real three dimensional solid for its existence. It is shown that the gap modes for various systems calculated
using this criterion are in reasonable agreement with the experimental values. The infrared behaviour of mixed crystals has
to be determined by examining the existence of local as well as gap modes for the two end members of the system. This generalized
new criterion successfully predicts the mixed mode behaviour of III–V mixed crystals besides predicting the one and two mode
behaviour, observed in infrared absorption of mixed alkali halioes and III-V compounds. 相似文献