Pressure dependence of elastic constants of trigonal Se and Te

The pressure dependence of the symmetric elastic constants of Se and Te are analyzed. The weaker interchain forces are shown to increase rapidly with decreasing interchain distances, whereas covalent intrachain forces decrease. The results are consistent with a picture of the bonding having a partially metallic contribution which increases as the crystals approach the actual phase transition to metallic structures, stable at higher pressures.     

Computation of collective excitations and elastic constants of expanded trigonal tellurium

The potential function derived from experimental structure factor data gives a repulsive minimum and also an attractive minimum. These two minima correspond to the first and second nearest-neighbour distances. Similar results have been obtained through the use of Percus-Yevick (PY) and hyper-netted chain (HNC) equations. The Hafner molecular dynamics results also show a similar trend. The first, second and third derivatives of the potential function have been obtained from the expression of the potential function. The first and second derivatives have been used to compute the phonon frequencies using Bhatia and Singh's (BS) method. The phonon frequencies obtained from Hubbard and Beeby's (HB) method show similar results. The elastic constants have also been calculated and the values obtained for C₁₁ by different methods are in good agreement. The Grüneisen constant has been calculated by two different methods which are in very good agreement with each other. From the Grüneisen constant the pressure derivative of the diffusion coefficient has been obtained and has been compared with that of Swalin's equation. The results are in excellent agreement with each other.     

Determination of the elastic constants of copper on copper-whiskers by the flexural vibration method

Copper-whiskers with different orientations were excited in flexural vibrational modes. From the resonance frequencies and the cubic compressibility, the elastic constants c_ik of copper were determined. The results are in good agreement with values obtained by other authors using other methods with macroscopic single crystals of copper. No enhancement of Young's modulus, reported recently in thin metallic films, was seen in Cu-whiskers.     

单向复合纤维材料弹性系数的超声测量

本文将单向复合纤维材料视作六角对称晶体，认为其弹性特征由五个独立的弹性系数来描述。利用Christoffel方程，我们得到这一各向异性介质中不同方向的声波速度与弹性系数的关系．我们还建立了一套计算机控制的实验测量系统，通过它对纤维板样品中的声速进行测量，反演得到了五个独立的弹性系数C11、C33、C13、C14和C12。理论计算得到的声速和实验测量值吻合较好，表明我们的方法是有实用意义的。     

Temperature dependence of the second-order elastic constants of cubic crystals

A simplified phenomenological theory of the temperature dependence of the second-order elastic constants of crystals is considered. The temperature dependences of the second-order elastic constants are calculated for a series of cubic crystals with various types of predominant chemical bonding. Satisfactory agreement between the calculation results and experimental data is obtained. Fiz. Tverd. Tela (St. Petersburg) 41, 235–240 (February 1999)     

Statistical theory of the elastic constants of nematic liquid crystals

A statistical mechanical theory of the Frank elastic constants is formulated. The free energy functional is constructed for the deformed sample and the free energy density is defined for the case of small spatial gradients. The Frank constants are expressed in terms of the direct correlation function c(1, 2) and the orientational single particle distribution function. For the example of Onsager spherocylinders three constants K ₁, K ₂ and K ₃ are calculated. The results of these calculations are similar to those given by Priest and by Straley.     

RUS study of the elastic constants in silver halide crystals

By using RUS method, the temperature dependence of the elastic constants in the silver halide crystals has been measured above room temperature. The elastic constants decrease linearly with increasing temperature. Numerical calculations are presented for the contribution of the multipole polarization to the elastic constants in the silver halide crystals. The calculated values of the deviation from the Cauchy relation are about a quarter of the experimental values. The multipole polarization significantly affects the elastic constants and contributes to the violation of the Cauchy relation.     

Determination of the elastic constants by coherent neutron scattering in polycrystals

It is shown that elastic constants which usually can be determined in single crystals only may be measured in polycrystals by inelastic coherent neutron scattering. Measurements are reported for polycrystalline samples of aluminium, copper and stainless steel. The method is best suited for the determination of the elastic constants connected with transverse phonons.     

Molecular forces and elastic constants of polyethylene single crystals

Polyethylene has an orthorhombic lattice for which nine elastic constants exist; they are obtained in terms of the intra- and intermolecular forces. Constants involved in the 6-12 Lennard-Jones potential approximating the London dispersion type of van der Waals' forces are obtained by computing the crystal potential energy and comparing it with the cohesive energy. First and second nearest-neighbor interactions are considered to establish relationship between the elastic constants and the interaction constants. The latter are obtained in terms of the C—C bond, stretching, bending, and repulsive force constants and the L-J potential constants. A limited type of central force assumption is applied. Values of Young and shear moduli are obtained along the three axes. The value along the chain compares with the experimentally determined and calculated values for oriented polyethylene. Young's modulus along the lateral direction is of the order of Young's modulus of bulk polyethylene, showing that intermo-lecular forces are the ones that determine the Young modulus of bulk polyethylene.     

Derivation of magnetostriction constants for ferrite single crystals by ferromagnetic resonance

Anisotropic elastic stresses are used with discs. Formulas are derived for the saturation magnetostriction constants in terms of the observed shifts in the resonance field. Results are reported for manganese, lithium, and yttrium ferrites.     

Adiabatic and isothermal elastic constants for highly anharmonic crystals

The mass operator of the phonon Green function for a highly anharmonic crystal in the ladder approximation is derived. In order to calculate the mass operator in the collision-dominated regime it is necessary to solve the Boltzmann-like equations. These solutions allow us to find the thermal conductivity coefficient and to prove that the thermodynamic relation between adiabatic and isothermal elastic constants is satisfied.     

高精度(Δ90°≤0.5″)长方体的制造技术

高精度(Δ90°≤0.5″)长方体的制造技术主要包括了加工方法和检测方法两个方面,即长方体的前期加工阶段采用立方体(方砖)形式加工,以保证一个直角的精度;后期是采用分离器单块精抛的加工方式,以保证其平行差。加工过程中用Φ150激光平面干涉仪检测和控制面形及平行度,用LY Φ80棱镜干涉仪检测和控制直角精度。这种制造技术可以将长方体的直角精度做到Δ90°≤0 5″。     

Many body forces and elastic constants of rare gas crystals

The effect of many body Van der Waals forces on the elastic constants of solid rare gases is calculated. These results are combined with contributions from the two body potential and zero point energy. The violation of the Cauchy relation is studied.     

Thermal characteristics of paratellurite single crystals by the rectangular thermal wave method

The study of the thermal characteristics of bulk nonferroelectric materials with low heat conductivity coefficient by the pyroelectrical rectangular thermal wave is shown to need the solution of the problem of the thermal conductivity for a three-layer system. The thermal characteristics of a paratellurite crystal with various crystallographic directions were studied. The heat conductivity coefficient is found to depend on the crystallographic direction.     

Contribution of the multipole polarization to the elastic constants in fluorite structure crystals

Numerical calculations are presented for the contribution of the multipole polarization to the elastic constants in fluorite structure crystals. The multipole polarizability is calculated by the self-consistent field treatment of the local density approximation and the spherical solid model. The elastic constants are significantly affected by the multipole polarization of the ions. The contributions of the multipole polarization of the ions to the elastic constant C₁₁, C₁₂, and C₄₄ are about 25%, 40% and 20% of the experimental values, respectively. The calculated values of the deviation from the Cauchy relation are in good agreement with the experimental values.     

Self-consistent theory of second order elastic constants for nonionic anharmonic crystals

Elastic constants of strongly anharmonic nonionic dielectric crystals are studied within the pseudoharmonic approximation by means of two-time Green functions. The relation between the method of homogeneous deformation by Leibfried and Ludwig and that of long waves is investigated. These considerations lead to a generalization of the method of homogeneous deformation for the case of strongly anharmonic crystals. A comparison between the results of the two methods shows that the pseudoharmonic approximation satisfies the exact elastic sum rule. On leave from the Institute of Theoretical Physics University of Wrocław, Wrocław, Poland.     

Temperature derivatives at constant volume of the elastic constants of alkali halide crystals

A new method has been developed for calculating the temperature derivatives at constant volume of the elastic constants of the alkali halides using the concept of phonon pressure. Calculated values of temperature derivatives of elastic constants are compared with the corresponding values recently derived from ultrasonic experimental data.