GGA and GGA+U Description of Structural, Magnetic, and Elastic Properties of Rh2MnZ (Z=Ge, Sn, and Pb)

Structural, magnetic, electronic, and elastic properties of Rh₂MnGe, Rh₂MnSn, and Rh₂MnPb Heusler compounds have been calculated using full potential linearized augmented-plane wave plus local orbitals (FP-L/APW+lo) method based on the spin density functional theory, within the generalized gradient approximation (GGA) and (GGA+U) (U is the Hubbard correction). Results are given for the lattice parameters, bulk moduli, spin magnetic moments and elastic constants. We have derived the bulk and the shear moduli, Young’s and Poisson’s ratio for Rh₂MnZ (Z=Ge, Sn, and Pb). The elastic modulus of Rh₂MnGe is predicted to be the highest. Also, we have estimated the Debye temperatures from the average sound velocity. We discuss the electronic structures, total and partial densities of states and local moments and we investigate the pressure effect on the elastic properties by calculating the elastic constants at various volumes.     

Determination of mass density, dielectric, elastic, and piezoelectric constants of bulk GaN crystal

Mass density, dielectric, elastic, and piezoelectric constants of bulk GaN crystal were determined. Mass density was obtained from the measured ratio of mass to volume of a cuboid. The dielectric constants were determined from the measured capacitances of an interdigital transducer (IDT) deposited on a Z-cut plate and from a parallel plate capacitor fabricated from this plate. The elastic and piezoelectric constants were determined by comparing the measured and calculated SAW velocities and electromechanical coupling coefficients on the Z- and X-cut plates. The following new constants were obtained: mass density p = 5986 kg/m(3); relative dielectric constants (at constant strain S) ε(S)(11)/ε(0) = 8.6 and ε(S)(11)/ε(0) = 10.5, where ε(0) is a dielectric constant of free space; elastic constants (at constant electric field E) C(E)(11) = 349.7, C(E)(12) = 128.1, C(E)(13) = 129.4, C(E)(33) = 430.3, and C(E)(44) = 96.5 GPa; and piezoelectric constants e(33) = 0.84, e(31) = -0.47, and e(15) = -0.41 C/m(2).     

Thermal and elastic properties of poly(vinyl chloride) (PVC) + chlorinated polyethylene (CPE) blends

Eight types of PVC + CPE blends with different weight ratios (PVC/CPE = 100/0, 90/10, 80/20, 60/40, 40/60, 20/80, 10/90, and 0/100) are tested. Data on the heat conductivity, thermal diffusivity, and heat capacity of the blends investigated are reported. Primary attention is paid to the structural approach for effective elastic constants: bulk, shear, and Young's modulae. The blends are considered as random mixtures of two isotropic constituents. It is found that the elastic moduli may be well represented by the Kerner and Budiansky equations.     

Two opposite effects of sodium on elastic constants of silicate binary glasses

(1 - x)SiO₂-xNa₂O glasses have been studied by Brillouin scattering when sodium oxide molar concentration x, varies in the range 0.05 < x < 0.44. Non-linear dependence of elastic constants on sodium oxide concentration is shown unambiguously for the first time and the compressive elastic constant C₁₁ experienced a non-monotonic behaviour with a minimum value around x = 0.15. These results are compared with those obtained previously in the case of other alkali silicate glasses (Li, K). The variations of elastic constants of these glasses with the alkali metal nature and concentration are discussed on the basis of relations with the molar density of silicon atoms and the force constants between modifiers and non-bridging oxygens.     

Pressure effects on elastic and thermodynamic properties of ZrB2

A theoretical formalism to calculate the single crystal elastic constants for hexagonal crystals from first principle calculations is described. The calculated values compare favorably with recent experimental results. An expression to calculate the bulk modulus along crystallographic axes of single crystals, using elastic constants, has been derived. The calculated linear bulk moduli are found to be in good agreement with the experiments. The shear modulus, Young’s modulus, and Poisson’s ratio for ideal polycrystalline ZrB₂ are also calculated and compared with corresponding experimental values. The shear anisotropic factors and anisotropy in the linear bulk modulus are obtained from the single crystal elastic constants. The Debye temperature is calculated from the average elastic wave velocity obtained from shear and bulk modulus as well as the integration of elastic wave velocities in different directions of the single crystal. The calculated elastic properties are found to be in good agreement with experimental values when the generalized gradient approximation is used for the exchange and correlation potential. It is found that the elastic constants and the Debye temperature of ZrB₂ increase monotonically and the anisotropies weaken with pressure. The thermal properties including the equation of state, linear compressibility, ductility, and the heat capacity at various pressures and temperatures are estimated.     

Low-temperature manganese contributions to the elastic constants of face-centred-cubic Fe-Cr-Ni stainless steel

By ultrasonic methods, we determined the elastic constants between 295 and 4 K of nominally Fe-18Cr-8Ni alloys (in wt%) containing up to 6% manganese. We report five elastic constants:C ₁ = longitudinal modulus,B = bulk modulus,E = Young modulus,G = shear modulus, and v = Poisson ratio. At all temperatures, manganese lowers all these elastic constants. With the exception of v, larger reductions occur at 4 K than at 295 K. At 4 K, the bulk modulus decreases more than the shear modulus: approximately 0.54 and 0.30% per per cent manganese, respectively. Manganese raises the magnetic-transition temperature, which occurs between 40 and 90 K, by approximately 9 K per per cent manganese. A simple model predicts the volume increase accompanying Mn alloying. However, a simple model fails to predict the elastic-constant reductions; this suggests magnetic interatomic interactions.     

Mg2Si弹性性质及热力学性质的第一性原理计算

采用基于第一性原理的赝势平面波方法系统地计算了Mg2Si弹性性质和热力学性质.根据计算数据得出Mg2Si在不同压强下的弹性常数,得出相对晶格常数(α/α0)、相对体积(V/V0)、体弹性模量与压强和温度的关系.通过准谐德拜模型计算了Mg2Si的热力学性质,如比热容和德拜温度,计算出的德拜温度与实验值基本相同.     

High-accuracy standard specimens for the line-focus-beam ultrasonic material characterization system

We prepared standard specimens for the line-focus-beam ultrasonic material characterization system to obtain absolute values of the propagation characteristics (phase velocity and attenuation) of leaky surface acoustic waves (LSAWs). The characterization system is very useful for evaluating and analyzing specimen surfaces. The calibration accuracy of these acoustic parameters depends on the accuracy of acoustical physical constants (elastic constants, piezoelectric constants, dielectric constants, and density) determined for standard specimens. In this paper, we developed substrates of non piezoelectric single crystals (viz., gadolinium gallium garnet [GGG], Si, and Ge) and an isotropic solid (synthetic silica [SiO₂] glass) as standard specimens. These specimens can cover the phase velocity range of 2600 to 5100 m/s for Rayleigh-type LSAWs. To determine the elastic constants with high accuracy, we measured velocities by the complex-mode measurement method and corrected diffraction effects. Measurements of bulk acoustic properties (bulk wave velocity and density) were conducted around 23°C, and bulk wave velocities were obtained with an accuracy of within ±0.004%. We clearly detected differences in acoustic properties by comparing the obtained results with the previously published values; the differences were considered to be due to differences of the specimens used. We also detected differences in acoustic properties among four SiO₂ substrates produced by different manufacturers     

Room temperature single crystal elastic constants of boron carbide

Single crystals of the high temperature ceramic boron carbide have been synthesized by the optical floating zone method. Room temperature elastic constants of a carbon-deficient boron carbide single crystal have been measured using the resonant ultrasound spectroscopy technique. Based upon density measurements, the single crystal stoichiometry was specified as B_5.6C. This crystal has room temperature single crystal elastic constants of c ₁₁ = 542.81, c ₃₃ = 534.54, c ₁₃ = 63.51, c ₁₂ = 130.59, and c ₄₄ = 164.79 GPa, respectively. Analysis of Cauchy's relationships, Poisson's ratios, and elastic anisotropic factors for the single crystal elastic constants indicates that it is more strongly anisotropic in elasticity and interatomic bonding than most solids. Room temperature isotropic elastic moduli of boron carbide show that its bulk, shear and Young's moduli are substantially higher than those of most solids, so that boron carbide belongs to the so-called strong solids. Its Poisson's ratio is significantly lower than that of most solids.     

Comparative study of the elastic properties of polycrystalline aluminum nitride films on silicon by Brillouin light scattering

Brillouin light scattering (BLS) has been used to investigate the elastic properties of polycrystalline AIN films, about 1 μm thick, grown by DC-reactive magnetron sputtering on Si₃N₄ coated (100)-Si substrates. Taking advantage from the detection of a number of different acoustic modes, a complete elastic characterization of the films has been achieved. The elastic constants c₁₁ and c₆₆ have been selectively determined from detection of the longitudinal and of the shear horizontal bulk modes, respectively, travelling parallel to the film surface. The three remaining elastic constants, namely c₄₄, c₃₃ and c₁₃, have been obtained from detection of the Rayleigh surface wave and of the longitudinal bulk wave propagating at different angles from the surface normal. The values of the elastic constants of these sputtered AIN films depend on the deposition conditions and on the microstructural properties of the films, especially oxygen contamination and quality of texture. In the case of the films with the best degree of texture and the lowest oxygen content, the values of the elastic constants are rather close to those previously determined in epitaxial A1N films grown at high temperature by MOCVD. This demonstrates that sputter deposition at relatively low temperature can be used to grow high quality A1N films on Si and is of great importance in view of the integration of these films in the technology of IC semiconductors.     

Prediction Study of the Mechanical and Thermodynamic Properties of the \hbox {RBRh}_{3} (R = Sm, Eu, Gd, and Tb) Compounds

The structural, elastic, and thermodynamic properties of the cubic anti-perovskite $\hbox {RBRh}_{3}$ (R = Sm, Eu, Gd, and Tb) compounds have been investigated using first principles full-potential augmented-plane wave plus local orbitals (FP-APW+lo) method with the generalized gradient approximation. The ground-state quantities such as the lattice parameter, bulk modulus, and its pressure derivative, as well as elastic constants are estimated. Computed equilibrium lattice constants agree well with the available experimental data. The full set of first-order elastic constants and their pressure dependence, which have not been calculated or measured yet, have been determined. The elastic moduli increase linearly with increasing pressure and satisfy the generalized elastic stability criteria for cubic crystals under hydrostatic pressure. The shear modulus, Young’s modulus, and Poisson’s ratio are calculated for ideal polycrystalline $\hbox {RBRh}_{3}$ aggregates. The Debye temperature is estimated from the average sound velocity. From the elastic parameter behavior, it is inferred that cubic anti-perovskites $\hbox {RBRh}_{3}$ are ductile in nature and that the bonding is predominantly of an ionic nature. Following the quasi-harmonic Debye model, the temperature effect on the lattice constant, bulk modulus, heat capacity, and Debye temperature is calculated reflecting the anharmonic phonon effects.     

Molecular Dynamics simulations of uniaxial and hydrostatic compression of C70 in the disordered phase

Classical Molecular Dynamics simulations have been performed for solid C₇₀ in the disordered f.c.c. phase using a spherically averaged Lennard-Jones potential. Each molecule was treated as a spherical shell of 70 carbons with radius of 3.8 Å. Tests imposing axial elongation with fixed lateral dimensions established the elastic constants C₁₁ and C₁₂. Axial deformation with zero lateral pressure was used to predict the Young modulus and the Poisson ratio. The bulk modulus was obtained by independent triaxial tension. These elastic results determined by regression analysis and digital filtering are compared to those of C₆₀ at 400 K and are in good agreement with those of Krzysztof et al. [K. Krzysztof, L.A. Girifalco, J.E. Fischer, J. Phys. Chem. 99 (1995) 16804] using the Girifalco potential.     

Effect of pressure on structural and elastic properties of alkaline-earth oxide CaO

We have performed ab initio calculations using a plane wave pseudopotential method to investigate the phase transition of alkaline-earth oxide CaO from NaCl (B1) to CsCl (B2) type structure. The elastic constants for this material have been determined in the pressure range 0–140 GPa. Also, the effect of hydrostatic pressure on the propagation elastic waves has been studied. The specific elastic constants, bulk modulus and wave velocities that we calculated for both B1 and B2 type structures are in good agreement with the available experiment data.     

薄膜和镀层力学性能的物理方法测试

讨论了薄膜和镀层力学性能的测试方法，包括布里渊散射、表面声波、声显微术及微压入方法。前三种方法是非接触法，最后一种是接触法。声学方法可测量弹性系数的各个分量，在薄膜和镀层情况下这些系数是和大块试样不同的，在弹性各向异性情况下可测出对应某个特定方向的弹性系数。微压入法只能测量各向同性的薄膜和镀层，但它还能测量若干塑性以至断裂的行为。最后，根据弹塑性理论进行的计算机数字模拟可以给出各种应力应变状态下的力学性能。     

Compositional dependence of the elastic constants and the Poisson ratio of GaxIn1−xSb

The pseudopotential method within the virtual crystal approximation combined with the Harrison bond-orbital model were used to determine all three elastic constants, and hence Poisson's ratio of Ga_xIn_1−xSb semiconductor alloys. Our results for parent compounds are compared to experiment and other theoretical calculations and showed generally good agreement. The effect of compositional disorder on the studied quantities has been examined. We found an important bowing in all elastic constants and bulk modulus versus Ga content. The Poisson ratio was found to be independent of alloy composition x.     

Elastic Constants of Mantle Minerals at High Temperature

A simple theoretical model is developed to investigate the temperature dependence of elastic constants. The method is based on a new expression for the temperature dependence of the bulk modulus and the formulation derived from Tallon’s model. The proposed relationship is applied to study the elastic constants of the solids of significance to geophysics applications. The calculated values of elastic constants are found to show good agreement with available experimental data.     

Stress in Thin Films;Diffraction Elastic Constants and Grain Interaction

Untextured bulk polycrystals usually possess macroscopically isotropic elastic properties whereas for most thin films transvers isotropy is expected,owing to the limited dimenionlity .The usually applied models for the calculation of elstic constants of polycrystals from single crystal elastic contants(so-called grain interaction models)erroneously predict macroscopic isotropy for an(untextured) thin film.This paper presents a summary of recent work where it has been demonstrated for the first time by X-ray diffraction analysis of stresses in thin films that elastic grain interaction can lead to macroscopically anisotropic behaviour (shown by non-linear sin^2φ plots).A new grain interaction model,predictin the macroscopically anisotropic behaviour of thin films,is proposed.     

First-Principles Calculations on Structure,Elastic and Thermodynamic Properties of Al2X （X=Sc,Y） under Pressure

To understand deeply the structural,elastic and thermodynamic characteristics of Al 2 X (X= Sc,Y) compounds in C15 type (space number 227) Cu 2 Mg structure,we have performed ab-initio density functional theory within the local density approximation (LDA) and the generalized gradient approximation (GGA).The thermodynamic properties of the considered structures are obtained through the quasi-harmonic Debye model.We have presented the results on the basic physical parameters,such as the lattice constant,bulk modulus,pressure derivative of bulk modulus,second-order elastic constants,Zener anisotropy factor,Poisson s ratio,Young s modulus,and isotropic shear modulus.In order to gain further information,the pressure-and temperature-dependent behaviour of the volume,bulk modulus,thermal expansion coefficient,heat capacity,entropy,Debye temperature and Gru¨neisen parameter were also evaluated over a pressure range of 0-20 GPa for Al 2 Sc and 0-17 GPa for Al 2 Y compound and a wide temperature range of 0-2000 K for both compounds.The obtained results were compared with the other reported values.     

Structural and elastic properties of TiN and AlN compounds: first-principles study

First-principles calculations of the lattice constants, bulk modulus, pressure derivatives of the bulk modulus and elastic constants of AlN and TiN compounds in rock-salt (B1) and wurtzite (B4) structures are presented. We have used the fullpotential linearized augmented plane wave (FP-LAPW) method within the density functional theory (DFT) in the generalized gradient approximation (GGA) for the exchange-correlation functional. Moreover, the elastic properties of cubic TiN and hexagonal AlN, including elastic constants, bulk and shear moduli are determined and compared with previous experimental and theoretical data. Our results show that the structural transition at 0 K from wurtzite to rock-salt phase occurs at 10 GPa and ?26 GPa for AlN and TiN, respectively. These results are consistent with those of other studies found in the literature.     

A method of determining acoustical physical constants for piezoelectric materials by line-focus-beam acoustic microscopy

We developed a new method of determining acoustical physical constants (elastic constant, piezoelectric constant, dielectric constant, and density) of piezoelectric materials with high accuracy. This method acquires velocities of leaky surface acoustic waves (LSAWs) excited on the water-loaded specimen surface, measured by line-focus-beam (LFB) acoustic microscopy, and bulk velocities of longitudinal and shear waves, measured with planewave transducers replacing the LFB device in the same system, together with the dielectric constants and density measured independently, for a small number of specimens. For LiNbO₃ and LiTaO₃ crystals, we demonstrated that we could accurately determine the constants by choosing proper propagation directions of LSAWs and bulk waves for three principal X-, Y-, and Z-cut specimens and one rotated Y-cut specimen [(104) plate for LiNbO₃ and (012) plate for LiTaO₃]. The accuracy is nearly the same as that for the constants determined only from the bulk wave velocities