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1.
The problem of the electron wind force acting on an impurity atom in a jellium metal, arising from the polarization of the electron density created by the flow of the electric current under a constant electric field, has been investigated. The impurity concentration is assumed to be small so that the impurity-impurity interaction can be neglected. We have used the scattering theory to treat the screening of the impurity by the electron gas in a nonlinear manner, and the pertubation due to the electric field is considered within the framework of the linearized Boltzmann equation. It is found that the driving force on the impurity can be expressed in terms of its residual resistivity, and this relationship is independent of the strength of the impurity potential. In the weak scattering limit the results of Bosvieux and Friedel are recovered. A close examination of the electronic polarization induced by the current, in the weak scattering limit, shows that there are terms in the electron density of second order in the impurity potential, which can be identified as the residual resistivity dipoles. However, their contribution to the driving force is found to be exactly zero.  相似文献   

2.
A simple theoretical analysis is presented for Mössbauer parameters and frequency moments of dilute57Fe impurities in different metallic hosts. These parameters have been evaluated for a general harmonic solid using Green's function method. Our results suggest that the contribution due to force constant change term is significant for the mean square displacement whereas that due to mass disordering term is predominating in the evaluations of mean square velocity. The variation of frequency moments for the impurity with host Debye-temperatures modified by the host to impurity mass ratios are shown for a number of solids.  相似文献   

3.
P D Semalty  P N Ram 《Pramana》1991,36(2):143-150
The elastic constants of dilute alloys based on bcc metals have been calculated using the Green’s function method obtaining explicit expressions for change in elastic constants in terms oft-matrix. The crystal impurity problem is discussed within an impurity model containing central and non-central force constant changes extended up to second neighbours of the impurity. The effect of volume change on elastic constants and a contribution from electron pressure term are considered. Numerical results for changes in three elastic moduli have been presented for a number of dilute alloys based on Mo, Nb, W, Ta and V.  相似文献   

4.
The low temperature electrical resistivity data on Al, Cu, Au, Ag, Pt, Mg, Sn, Zn, In and Ga are reviewed with particular emphasis on the variation of the phonon contribution with the magnitude of the impurity resistivity. A comparison is made within the various alloys having the same base metals, and also between the different solvents, by developing a phenomenological fitting formula for the deviations from Matthiessen's rule. The derived phenomenological parameters show a strong similarity for all metals. The limits imposed on this type of comparison by the uncertainty of data obtained on different samples and in different laboratories are discussed.

An updating of the references given in an earlier review in this journal by Bass (1972) is also included.  相似文献   

5.
The experimental data related to the electric field gradient at transition impurities either in hexagonal metals, or in cubic metals where the isotropy is perturbed by a next impurity, can be explained neither by the lattice contribution nor by the electronic contribution from the conduction band. A model is proposed here to investigate the electronic contribution arising from virtual bound 3d states on the impurity, by studying the local crystal field influence in a Friedel-Anderson model. It appears that at the 0°K limit, the localized electronic contribution to the EFG can be linearly related to the density nd(?F) of 3d states at the Fermi level. As a first approximation, this law is valid even at temperature different from 0°K so establishing a linear correlation between the EFG, the impurity resistivity and the amplitude of the charge perturbation around the impurity.  相似文献   

6.
顾世杰 《物理学报》1965,21(4):787-801
在这篇文章中,我们用一维晶格模型讨论了杂质中心中电声子耦合强度的问题。用场论方法严格地解得了含杂质晶格之运动方程的本征函数。由此得到了电声子耦合强度的解析表示式,它是用声子的波数k、表示相互作用范围的参量λ以及杂质参量P=γ′/γ解析地表示出来的。其中γ′和γ分别为杂质与近邻之间和一般近邻之间的力常数。对结果的分析表明,只改变质量的杂质不影响电声子耦合;导致力常数变化的杂质对电声子耦合有显著的影响。当有奇的局域模出现时,在离子晶体中它对带宽的贡献可以比带内模的贡献大很多。尤其是在离子晶体中有可能出现所谓“临界散射”,这时带内模的贡献可能变得很小,而主要的贡献几乎全来自于局域模。相反地,在非极化晶体中,局域模的贡献一般是很小的。文中最后讨论了由一维模型得到的结论对于三维晶体可能有的意义。  相似文献   

7.
We investigate the relaxation of the normal electrical resistivity, induced by high-pressure in YBa2Cu3O6.45 single crystals. It is determined that the pressure affects to the phase composition of the sample. Under pressure phases with different (but similar) critical temperatures form. It is determined that the application-removal pressure process is completely reversible. Above Tc the temperature dependence of the resistivity in the layers' plane at different hydrostatic pressures can be approximated with high accuracy with the scattering of electrons by phonons model. With increasing pressure, the residual resistance is reduced and the contribution of intraband s–s scattering increases. Additionally, the role of the interband s–d scattering and the Debye temperature is enhanced.  相似文献   

8.
Precise measurements of the electrical resistivity as a function of temperature on 16 samples with Fe concentrations varying between 0.2 and 12ppm have revealed a linear temperature dependence of the magnetic impurity scattering for Fe concentrations ? 3 ppm. Deviations from Matthiessen's rule appear to become negligibly small below 5°K for all samples despite a variation of 2 orders of magnitude in the residual resistivities of the samples considered. Above 5°K the deviations from Matthiessen's rule are found to undergo a remarkably rapid increase with temperature yet their magnitudes appear to be unrelated to the residual resistivities or the Fe concentrations of the samples.  相似文献   

9.
Analysis of Soffer's size-effect theory for electrical resistivity shows, for measurements in such a T range for which the temperature dependent portion of the resistivity, ρi, is always much smaller than the residual bulk resistivity ρ(0) of the metal studied, that while size-effects leave the essential T dependence of ρi unchanged, it may increase its absolute value and the observed residual resistivity ρ(0), thus explaining recent results of Caplin et al. This also corrects the general conclusion arrived at by the latter authors, i.e. that the T dependence of ρ of a metal foil of given residual resistivity is the same as that of a bulk sample of the same residual resistivity provided that the latter is governed by impurity scattering, as being true for a narrow T range only, i.e. for which ρi(T) ? ρ(0). However, for this T range a procedure is outlined which allows one to extract values of the surface specularity parameter pS and also ρ of the metal foils studied.  相似文献   

10.
11.
《Surface science》1997,373(1):L345-L349
The free-energy contribution of phonons to surface reconstruction of Pd 110 is studied by Green's function methods. The adsorbate is modelled as a local perturbation to the dynamical matrix, the effect of which is solved from Dyson's equation. The phonons have a high entropy at the reconstructed surface, thus easing the reconstruction as the temperature increases. Adding an impurity atom with a low Debye temperature further enhances the entropy effect in favour of reconstruction.  相似文献   

12.
CeInCu2 is a heavy fermion compound close to magnetic instability. The electrical resistivity has aT 2 behaviour between 1 and 2.5 K. and the AC field susceptibility has a faint maximum at 0.9 K, indicating the onset of coherence near 1 K for this compound. The magnetoresistance keeps a negative sign down to 0.3 K. Neutron inelastic scattering give a crystal field splitting of 90 K, with a doublet ground state, and a residual quasielastic linewidth of 0.3 meV.We have studied the resistivity, susceptibility and specific heat of some dilute solutions La1–xCexInCu2 and Y1–xCexInCu2. The spin-dependent part of the resistivity may be decomposed into a single impurity term plus a pair interaction term, the magnitude of which folows a Curie-Weiss law, as in classical spin glassesCuMn orAuFe.The magnetisation and susceptibility at low temperatures may be represented within the resonant level model, taking into account antiferromagnetic interactions. Finally, the specific heat of CeInCu2 shows a bump near 2.3 K, absent for dilute solutions, which may also be interpreted by introducing a magnetic interaction term.  相似文献   

13.
The electronic structure and the residual resistivity of random FeRh-based alloys in the CsCl structure are calculated for different spin configurations using the tight-binding linear muffin–tin orbital method. The effect of substitutional impurities (Pd, Rh) is described by means of the coherent potential approximation. It is shown that impurity scattering leads to giant magnetoresistance effects in qualitative agreement with experiment.  相似文献   

14.
The question of the residual resistivity of chemically pure metals which are mixtures of atoms of different isotopes is discussed. The question of the static displacements appearing near isotopic impurities due to differences in the zero-point vibrations is analyzed in a microscopic approach. It is shown that such static displacements have a significant influence on the residual resistivity ρr. Their contribution to ρr is far greater than the contribution due to differences in the dynamic elastic electron scattering amplitudes. Zh. éksp. Teor. Fiz. 114, 2153–2165 (December 1998)  相似文献   

15.
The resistivity of aluminum based alloys containing V, Fe, Co, Ni and Cu has been measured between 4.2 and 100°K. The wide range of concentrations covered by our samples was obtained by the use of a rapid quenching technique, and the highest impurity resistivity is more than one order of magnitude higher than the interval previously explored.It is found that previous observations of a phonon resistivity varying as T3 and depending only on the impurity resistivity are still valid also in this range.  相似文献   

16.
The change of the phonon contribution to the free energy, ΔF, due to the interaction between an adatom and an impurity substrate atom is calculated by expressing ΔF as a contour integral in the complex-frequency plane and evaluating it directly along a suitably chosen contour numerically. Results are given as a function of the adatomsurface bond force constant, the mass defect of the impurity atom, and the adatomimpurity separation for both a one-dimensional and a three-dimensional simple cubic model substrate.  相似文献   

17.
对于深能级杂质,通常的有效质量近似已不再成立。本文由Bloch波函数出发,应用赝势的概念,证明了杂质波函数及能级满足一等效的薛定谔方程。其中除包含通常的长程库仑位势外,还有一短程位势,后者随不同杂质原子而异。对浅能级杂质,它引起谷-轨道分裂,但对深能级杂质,它已不能看成微扰项了。我们讨论了这部分短程位势对杂质束缚能级的影响。只有当等效势阱深到足以单独地引起电子的共振散射或束缚态时,它对杂质束缚能级才有很明显的影响,束缚能级随此势阱加深而迅速增加。此外可以证明,短程作用的带间矩阵元可以近似用一等价带内排斥势来代替,当束缚能接近禁带宽度时,带间作用影响很大。我们指出,带间作用可以解释为什么杂质能够同时俘获电子和空穴。通过一个简单的例子,我们进行了具体的数值计算,并进一步分析了短程作用的影响。最后我们利用这个简单模型讨论了Cu,Ag,Au在Ge中的能级。  相似文献   

18.
A quantitative calculation of the residual electrical resistivity of dilute ferromagnetic nickel-based alloys has been performed in the framework of the four-current conduction model using the kinetic equation and ab initio approaches for and ab initio approaches for the determination of the scattering potential. The contributions to the residual electrical resistivity from scattering by inhomogeneities of the impurity Coulomb potential and the exchange interaction have been separated by comparing the calculated and experimental data.  相似文献   

19.
When a polymer is dissolved in a solvent, the heat measured is a sum of a polymer-solvent interaction term and a term related to the structure that existed in the solid polymer relative to its amorphous liquid state. This latter contribution, termed the “residual” heat, can have an endothermic contribution due to the fusion of crystalline regions and an exothermic contribution due to the disruption of structure in noncrystalline amorphous regions. For atactic polystyrene between 30 and 110°C, it is shown that the “residual” heat is exothermic, decreases linearly with temperature differences below Tg, and extrapolates to zero in the vicinity of Tg. The existence of an exothermic heat above Tg is probably related to a 160°C transition in polystyrene. This “residual” heat was further observed to be independent of the pressure at which the polystyrene was glassified.  相似文献   

20.
为保证空间惯性传感器的正常在轨运行,在发射阶段需保证测试质量固定以避免与周围电容极板的接触碰撞;到达预定轨道后再重新捕获并以最小残余线速度将测试质量释放至精确位置,保持自由悬浮状态。测试质量的捕获定位对驱动器提出高精度的要求。本文针对在太空中捕获定位释放测试质量所用的压电直线驱动器进行了设计定制与性能测试。试验结果表明:该定制的压电驱动器最小步长小于1 nm,但步长稳定性误差较大;150 V工作电压条件最大驱动力达72 N;单步行进驱动力稳定;夹持测试质量过程中,驱动力稳定,稳定性偏差为0.16%。满足捕获、定位、释放机构的使用需求。  相似文献   

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