Universal LCAO parameters for III–V compound semiconductors

A set of semi-empirical expressions for the two-center integrals which enter the Slater-Koster parameters are constructed for Group III–V compound semiconductors These expressions show their explicit dependence on the atomic characteristics, on the dielectric constant, on the lomcity of solids, and also on the interatomic separations, and they are valid for atomic separations as far as second-neighbor distances For zero ionicity they reduce to those obtained previously by us for Group IV semiconductors The Slater-Koster parameters are then constructed from these expressions for the two-center integrals The band structures of various gallium and indium compounds are obtained and are compared with other theoretical calculations and with experimental photoemission results     

Lattice dynamics of molecular solids by a phenomenological model

A quasiharmonic central-force rigid-atom model has been used to study the dispersion of phonon waves in molecular (rare-gas) solids. The model derives the interatomic forces by Buckingham-Corner potential and takes account of all neighbor interactions. Zero-point anharmonic effects have been taken into account through the potential parameters by a method of iteration. It is found that out of all the conventional power and exponential potentials the Buckingham-Corner potential function is best suited to this class of molecular solids. Further, the possibilities of the improvement of the present model have been discussed.     

Inelastic collisions of medium energy atomic elements in solids

The stopping of medium atomic elements in solids has been calculated in the framework of classical approximation, taking into account elastic and inelastic collisions. The calculations are based on the 1) revised equations for the law of energy and impulse conservation, which were earlier used to describe inelastic collisions of atomic particles, 2) theory of quasi-small angle scattering, 3) power potential of LNS, and 4) limitation of the maximum distance of atoms approach determined by the interatomic distance in solids. Analytical equations have been obtained to calculate 1) a differential cross-section of elastic scattering in the presence of inelastic collisions, 2) energy transferred, 3) cross-sections of elastic and inelastic stopping, and penetration depth. Implantation into solids was found to be of threshold character.     

Application of the Bogolyubov inequality for the calculation of the thermodynamic properties of diatomic molecules

The frequency of vibration and the interatomic distance are considered as variational parameters in an approximate expression for the free energy of a diatomic molecule. Application of the Bogolyubov inequality allows one to find the dependence of these parameters on temperature. Calculations are given for the molecules HF and HgH.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 6–8, January, 1982.     

Fifty years of Szigeti’s dielectric theory — A review

During the period 1949–1961 Szigeti published four seminal papers on the dielectric behaviour of crystals. Szigeti’s theory is applicable to isotropic and anisotropic, ionic and covalent crystals with different structures. Szigeti’s theory connects dielectric, spectroscopic and elastic properties. An important outcome of Szigeti’s theory is the concept of the effective ionic charge (s). It is pointed out that s correlates with a number of physical properties and is a measure of ionicity of the interatomic bond. Since Szigeti’s work, several theoretical models have been proposed to account for the fact that s < 1. These models provide an insight into the complex polarization mechanisms in solids. This review summarizes Szigeti’s work and the work that followed; the implications and applications of Szigeti’s theory are discussed. Some new results are also included. Dedicated to the memory of late Prof. P S Narayanan.     

利用电子结构数据拟合H2分子的电子壳模型势函数参数

电子壳模型势函数在离子晶体的原子级计算机模拟中有广泛应用,其势参数主要通过拟合晶体的实验数据或电子结构数据得到.提出了通过拟合双原子分子的量子化学从头计算电子结构数据来获得该势函数的方法,并由H₂分子的电子结构数据建立了H原子间的电子壳模型势函数.此外,还应用该势函数对H⁺₂分子离子进行了计算.该势函数拟合方案更适合于共价键型的分子. 关键词： 电子壳模型势 参数拟合 共价键 2分子')" href="#">H₂分子     

Investigation of glassy behavior in lead barium ytterbium tantalate relaxors

The glassy behavior of lead barium ytterbium tantalate relaxors has been investigated. The frequency dependence of the temperature, T′_m (the temperature corresponding to the maximum value dielectric constant) is analyzed using Vogel-Fulcher relation and power law. The fitting parameters reveal that the power law explains the relaxation mechanism much better than the Vogel-Fulcher relation. The temperature dependence of dielectric constant at temperatures much higher and lower than T′_m is analyzed by two exponential functions, which gives an idea about the production of polar clusters at high temperature and the distribution of freezing temperatures at lower temperature.     

利用电子结构数据拟合H2分子的电子壳模型势函数参数

电子壳模型势函数在离子晶体的原子级计算机模拟中有广泛应用,其势参数主要通过拟合晶体的实验数据或电子结构数据得到.提出了通过拟合双原子分子的量子化学从头计算电子结构数据来获得该势函数的方法,并由H2分子的电子结构数据建立了H原子间的电子壳模型势函数.此外,还应用该势函数对H+2分子离子进行了计算.该势函数拟合方案更适合于共价键型的分子.     

Natures of Statefinder Parameters and Om Diagnostic for Cardassian Universe in Ho?ava-Lifshitz Gravity

In this work, we have considered Cardassian Universe in Ho?ava-Lifshitz gravity. Four types of Cardassian Universe models i.e., polytropic/power law, modified polytropic, exponential and modified exponential models have been considered for accelerating models. The natures of statefinder parameters, deceleration parameter, Om diagnostic and EoS parameters have been investigated for all types of Cardassian models in Ho?ava-Lifshitz gravity.     

Quantum-mechanical modeling without wave functions

It has been shown that the variational principle can be used as the practical way to find the electron density and the total energy in terms of the density functional theory without solving the Kohn-Sham equations (the so-called orbital-free approach). The equilibrium interatomic distances and binding energies found using examples of diatomic systems Si₂, Al₂, and P₂ are in good agreement with the published data. The results obtained for Si-Al, Si-P, and Al-P dimers are also close to the results obtained by the Kohn-Sham method.     

Electrical properties of pure and Li2O-doped CuO/Fe2O3 system precalcined at different temperatures

The electrical properties of pure and Li₂O-doped CuO/Fe₂O₃ solids were investigated. Pure and variously doped solids were subjected to thermal treatment at 1073–1273 K and the amount of dopant was varied between 0.84 to 3.36 mol%. The effect of precalcination temperature and amount of Li₂O added on the electrical conductivity σ, activation energy E_a and dielectric constant * were studied. The variation of ′ and ″ as a function of frequency for pure and variously doped solids precalcined at different temperatures was also investigated. The results obtained were discussed.     

Antibunching and blinking from a single colloidal CdSe quantum dot

We have investigated the optical properties of single CdSe/ZnS nanocrystals by conducting combinations of experiments on antibunching and photoluminescence intermittence under different experimental conditions.Based on photoluminescence in an antibunching experiment,we analyzed the emission lifetime of QDs by using stretched exponentials.The difference between the parameters obtained from average lifetimes and stretched exponents were analyzed by considering the effect of nonradiative emission.An Auger-assisted tunneling model was used to explain the power law exponents of off time distribution.The power law exponent under high excitation power was correlated with a higher Auger ionization rate.Using the parameters obtained from stretched exponential function and power law,the antibunching phenomena at different time and under different excitation intensity were analyzed.     

具有在位势的一维双原子链晶格振动的色散关系

在简谐近似下,求解具有在位势的一维双原子链晶格振动运动方程,得到了具有在位势的晶格振动的色散关系.在位势使色散关系声频支在布里渊区中心的振动频率不再为零,并且随在位势的增大而增大.对于原子之间相互作用势不随在位势大小变化的情况下,晶格振动的色散关系的频隙随在位势的增大而变宽.讨论了原子链由只有在位势的不连续极限(AC极限),通过在位势逐渐减弱而原子间相互作用势逐渐增强,最后演变到只有原子间相互作用势的原子链的情况.随着在位势减弱和相互作用势增强,色散关系的频隙由AC极限的孤立轻、重原子简谐振动频率之差逐渐变化到通常的无在位势的色散关系频隙.     

Study of dielectric anisotropy and other related parametersof a liquid crystal compound 7OAOB

Temperature-dependent dielectric anisotropy has been measured for the compound 4,4′-di-n-heptyloxy-azoxy benzene (7OAOB) by using a digital LCR bridge (HIOKI 3532-50 LCR HiTESTER). The compound 7OAOB is found to exhibit negative dielectric anisotropy in the nematic and smectic-C phase. Frequency-dependent electrical conductivity has been measured for this compound. The dc conductivity has also been obtained from frequency-dependent total conductivity studies by using universal power law equation. The activation energy of the dc conduction process and relaxation time has been determined in different mesophases. The behavior of splay elastic constant (K₁₁) with temperature has been examined for this compound. From the studies of UV-visible spectra, the values of energy band gap have been evaluated.     

The influence,on lithium electrochemical intercalation,of bond ionicity in layered chalcogenophosphates of transition metals

In the course of lithium electrochemical intercalation in the host structure of layered M∥PX₃ phases (M = V, Mn, Fe, Co, Ni, X = S, Se), it was shown that the best energy yield was obtained from low ionicity bond materials. The absorption edge energy, along with the free energy of the intercalation reactions have been correlated in a satisfactory way to the ionicity fi of the M-X bonds. These diagrams indicate which phases have to be looked at to obtain the maximum electrochemical yields.     

An Ising model for the stress relaxation of solids

A kinetic theory of stress relaxation of solids as a cooperative process is proposed. The theory is based on a two-state model for the relaxation. It is shown that the conventional mean field approximation leads to an exponential dependence of the rate of stress relaxation on the stress while the multiplicative approximation of Vol'kenstein et al. leads to a power law. It is argued that the exponential law should be valid initially in the relaxation process while the power law is appropriate when the system is nearer equilibrium, which is in qualitative agreement with recent experimental findings.     

Effect of Li2O doping on electrical properties of CoFe2O4

The solid–solid interactions between cobalt and ferric oxides to produce CoFe₂O₄ were followed up using XRD investigation. The effect of Li₂O-doping on the ferrite formation was also studied. The electrical and dielectric parameters of pure and doped mixed solids precalcined at 1273 K were measured using d.c and a.c instruments.The dopant concentration was varied between 0.5 and 6 mol% Li₂O. The results obtained revealed that Li₂O doping much enhanced the ferrite formation due to an increase in the mobility of the reacting species.

The addition of the smallest amount of Li₂O (0.5 mol%) resulted in measurable variations in the electrical constants (ρ, E_a, ′, ″ and tan δ). Resistivity increased upon increasing the dopant concentration up to 1.5 mol% exceeding the values measured for the undoped sample. Furthermore, the presence of 6 mol% Li₂O brought about a significant decrease of electrical resistivity. Also, the activation energy decreased with increasing the dopant concentration. The dielectric constant behaves according to ε=const. 1/ρ^1/2.

The Li₂O-doping modified the values of different dielectric constants, the change in these constants was found to be strongly dependent on the amount of Li₂O added.These results have been discussed in terms of the potentiality of Li₂O in increasing the mobility of the reacting species involved in the ferrite formation.     

Analysis of effective compressibilities in PbS,PbSe, PbTe and SnTe

An analysis of effective compressibilities in ionic semiconductors PbS, PbSe, PbTe and SnTe has been performed within the framework of many-body lattice theory (MLT). The extended three-body force shell model (ETSM) has been employed to obtain the values of effective compressibilities in the solids under study. The model parameters have been calculated using the expressions for elastic and dielectric constants within the framework of the ETSM. It is found that the predicted values of β¹/β agree fairly well with the results obtained from the Szigeti relation.     

Diagrammatic method for the calculation of short-range order effects in an ordering binary alloy

A statistical thermodynamic theory of short-range order effects in an ordering binary alloy with an arbitrary composition and an arbitrary radius of the interatomic interaction has been constructed in the approximation of ring diagrams for the free energy. For concreteness, a solid solution, which orders according to the Cu₃Au type, has been considered. A formula has been obtained for the Fourier components of the correlation parameters, which is valid for a wide range of variation of concentration and temperature of the alloy. Correlation parameters of the system Cu₃Au with a stoichiometric composition have been calculated according to this formula for given values of the displacement energy for various coordination spheres at several values of temperature and the interaction radius.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 62–67, August, 1988.The authors thank D. M. Sedrakyan and É. M. Kazaryan for a discussion of the results.     

尾流效应对快速双原子分子离子在固体中电荷态及分子轴取向的影响

研究了快速双原子分子离子在固体中穿行时,尾流效应对各离子电荷态以及库仑爆炸过程的影响.借助于线性介电响应理论和局域介电函数,离子之间的动力学相互作用势可以表示成对称的屏蔽库仑势和非对称的尾势.通过对分子离子上所有束缚电子的总能量进行变分和求解单个离子的运动方程,自洽地确定出分子离子中每个离子的电荷态.数值结果表明,由于尾流效应的影响,在初始穿行阶段,分子离子中导航离子的电荷数随穿行深度的增加而单调递增,而尾随离子的电荷数则随穿行深度的增加而振荡.但当穿行深度很大时,两个离子的电荷数都趋于具有相同速度的孤立离子的电荷数.此外,还发现分子轴的取向朝入射速度方向偏转