Structural,mechanical and thermo physical properties of III–V yttrium pnictides with NaCl-structure under high pressure

In the present paper, we have investigated the high-pressure structural phase transition of yttrium pnictides (YX; X = N, P, As and Sb). An extended interaction potential (EIP) model has been developed (including the zero point energy effect in three body interaction potential model). Phase transition pressures are associated with a sudden collapse in volume. The phase transition pressures and associated volume collapses obtained from present potential model show a generally better agreement with available experimental data than others. The elastic constants and their pressure derivatives are also reported. Moreover the thermo physical properties have also been obtained successfully. Our results are in general in good agreement with experimental and theoretical data where available, and provide predictions where they are unavailable.     

High pressure structural (B1–B2) phase transition and elastic properties of II–VI semiconducting Sr chalcogens

We evolve an effective interionic interaction potential (EIoIP) with long-range Coulomb interactions and the Hafemeister and Flygare type short-range overlap repulsion extended up to the second neighbor ions and the van der Waals (vdW) interaction to discuss the pressure induced structural aspects of NaCl-type (B1) to CsCl-type (B2) structure in alkaline earth chalcogenides (SrX; X = S, Se and Te). Particular attention is devoted to evaluate the vdW coefficients following the Slater–Kirkwood variational method, as both the ions are polarizable. The present calculations have revealed reasonably good agreement with the available experimental data on the phase transition pressures (P_t = 17.5, 14.5, 12.5 GPa) and the elastic properties. The calculated values of the volume collapses [ΔV(P)/V(0)] are also closer to their observed data. Further, the variations of the second- and third-order elastic constants with pressure have followed a systematic trend, which are almost identical to those exhibited by the observed data measured for other semiconducting compounds with rocksalt (B1) type crystal structure. Also the Born and relative stability criteria is valid in strontium monochalcogenides.     

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.     

Third-order elastic constants and pressure derivatives of the second-order elastic constants of hexagonal boron nitride

The second and third order elastic constants and pressure derivatives of second order elastic constants of hexagonal boron nitride have been obtained using the deformation theory. The strain energy derived using the deformation theory is compared with the strain dependent lattice energy obtained from elastic continuum model approximation to get the expressions for second and third order elastic constants. Higher order elastic constants are a measure of anharmonicity of crystal lattice. The six second-order elastic constants and the ten non-vanishing third order elastic constants and six pressure derivatives of hexagonal boron nitride are obtained in the present work and are compared with available experimental values. The second order elastic constant C ₁₁ which corresponds to the elastic stiffness along the basal plane of the crystal is greater than C ₃₃. Since C ₃₃ being the stiffness tensor component along the c-axis of the crystal, this result is expected from a layer-like material like boron nitride (BN). The third order elastic constants of hexagonal BN are generally one order of magnitude greater than the second-order of elastic constants as expected of a crystalline solid. The pressure derivative dC ₃₃/dp obtained in the present study is greater than dC ₁₁/dp which indicates that the compressibility along c-axis is higher than that along ab-plane of hexagonal BN.     

A density functional study of structural and elastic properties of LaN under high pressure

Structural and elastic properties of LaN at normal and high pressures are investigated using ab initio calculations based on full-potential linearized augmented plane wave (FP-LAPW) within both local density approximation (LDA) and generalized gradient approximation (GGA). Our results concerning equilibrium lattice parameter and bulk modulus agree well with the available experimental and previous theoretical findings. The transition pressure from NaCl (B1) to CsCl (B2) phase is found to be 31.05 GPa from LDA, and 42.2 GPa from GGA. To the best of our knowledge, the elastic properties for LaN in the B1 structure in the presence of pressure have never been reported so far. The linear pressure coefficients of elastic constants and their related bulk modulus are determined from the pressure dependence of these parameters. Furthermore, the mechanical stability criteria for LaN in B1 phase are found to be fulfilled at normal conditions.     

The elastic properties, elastic models and elastic perspectives of metallic glasses

Bulk metallic glass (BMG) provides plentiful precise knowledge of fundamental parameters of elastic moduli, which offer a benchmark reference point for understanding and applications of the glassy materials. This paper comprehensively reviews the current state of the art of the study of elastic properties, the establishments of correlations between elastic moduli and properties/features, and the elastic models and elastic perspectives of metallic glasses. The goal is to show the key roles of elastic moduli in study, formation, and understanding of metallic glasses, and to present a comprehensive elastic perspectives on the major fundamental issues from processing to structure to properties in the rapidly moving field.A plentiful of data and results involving in acoustic velocities, elastic constants and their response to aging, relaxation, applied press, pressure and temperature of the metallic glasses have been compiled. The thermodynamic and kinetic parameters, stability, mechanical and physical properties of various available metallic glasses especially BMGs have also been collected. A survey based on the plentiful experimental data reveals that the linear elastic constants have striking systematic correlations with the microstructural features, glass transition temperature, melting temperature, relaxation behavior, boson peak, strength, hardness, plastic yielding of the glass, and even rheological properties of the glass forming liquids. The elastic constants of BMGs also show a correlation with a weighted average of the elastic constants of the constituent elements. We show that the elastic moduli correlations can assist in selecting alloying components with suitable elastic moduli for controlling the elastic properties and glass-forming ability of the metallic glasses, and thus the results would enable the design, control and tuning of the formation and properties of metallic glasses.We demonstrate that the glass transition, the primary and secondary relaxations, plastic deformation and yield can be attributed to the free volume increase induced flow, and the flow can be modeled as the activated hopping between the inherent states in the potential energy landscape. We then propose an extended elastic model to understand flow in metallic glass and glass-forming supercooled liquid, and the model presents a simple and quantitative mathematic expression for flow activation energy of various glasses. The elastic perspectives, which consider all metallic glasses exhibit universal behavior based on a small number of readily measurable parameters of elastic moduli, are presented for understanding the nature and diverse properties of the metallic glasses.     

Structural elastic and thermal properties of Sr x Cd1−x O mixed compounds — a theoretical approach

In the present paper, the structural and mechanical properties of alkaline earth oxides mixed compound Sr _x Cd_1?x O (0 ? x ? 1) under high pressure have been reported. An extended interaction potential (EIP) model, including the zero point vibrational energy effect, has been developed for this study. Phase transition pressures are associated with a sudden collapse in volume. Phase transition pressure and associated volume collapses [ΔV (Pt)/V(0)] calculated from this approach are in good agreement with the experimental values for the parent compounds (x = 0 and x = 1). The results for the mixed crystal counterparts are also in fair agreement with experimental data generated from the application of Vegard’s law to the data for the parent compounds.     

Structural phase transition,electronic and elastic properties in TlX (X = N,P, As) compounds: Pressure-induced effects

Using the first-principles plane-wave pesudopotential (PW-PP) method with the generalized gradient approximation (GGA) for the exchange-correlation potential, we have studied the structural, electronic and elastic properties of TlX (X = N, P, As) compounds under hydrostatic pressure. Our calculations show that TlN, TlP and TlAs undergo a phase transition from the zincblende (ZB) to the rocksalt (RS) structure at 19.05, 7.29 and 5.01 GPa, with a volume collapse of 14.96%, 17.45% and 18.03%, respectively. The influence of crystallographic structure and hydrostatic pressure on electronic band structures, elastic constants, and aggregate bulk moduli are investigated. Further, the elastic wave velocities, Debye temperatures and melting temperatures for zincblende TlN, TlP and TlAs compounds are obtained. Our calculated results are compared with the previously reported theoretical data.     

Elastic properties of CeRu2

We present data of the elastic properties of the Laves phase compound CeRu₂ in the normal and superconducting state obtained from ultrasound measurements. In the temperature range between the superconducting transition temperature of 6.1 K and 300 K we used a deformation potential coupling approach to describe the temperature dependence of the elastic constants. The elastic anomalies in the superconducting state are characterised with the model of thermally assisted flux flow (TAFF). This enables us to construct a detailed superconducting B-T phase diagram including the vortex dynamics and interpret the peak effect region. Especially the ultrasonic measurements exhibit clearly the connection between the normal state and the superconducting properties. They show that structural fluctuations have strong effects on the superconductivity and on the vortex dynamics.     

Elastic anisotropy and low-temperature thermal expansion in the shape memory alloy Cu-Al-Zn

Cu-based shape memory alloys are known for their technologically important pseudo-elastic and shapememory properties, which are intimately associated with the martensitic transformation. A combination of deformation theory and finite-strain elasticity theory has been employed to arrive at the expressions for higher order elastic constants of Cu-Al-Zn based on Keating's approach. The second- and third-order elastic constants are in good agreement with the measurements. The aggregate elastic properties like bulk modulus, pressure derivatives, mode Grüneisen parameters of the elastic waves, low temperature limit of thermal expansion, and the Anderson-Grüneisen parameter are also presented.     

Measurement of ultrasonic wave velocity in a solid under gas pressures up to 0·4 GPa

A set-up is described for the measurement of longitudinal and transverse wave velocities in a solid under gas pressures up to 0·4 GPa. To check the performance of the set-up, the elastic constants of Se and As₂Se₃ glasses and their pressure derivatives were obtained from the wave velocity data and compared with the data available in the literature.     

Higher order elastic constants of rare earth metals: gadolinium,dysprosium and erbium

The expressions for the second and third order elastic constants of the rare earth metals, gadolinium dysprosium and erbium have been worked out and their values have been determined. The present theoretical values are compared with the experimentally observed results. It is also suggested that the third order elastic constants of these metals may be measured using ultrasonic technique under high pressures.     

Theoretical Investigation of the Phase Transition,Elastic and Superconductivity Properties of LaS Under Pressure

The first-principles method has been performed to investigate the phase transition, elastic, thermodynamic and superconductivity properties of lanthanum monosulphide (LaS) under pressure. A structural phase transition from the NaCl-type (B₁) to CsCl-type (B₂) structure is found to occur at around 16.8 GPa. The calculated ground state properties such as lattice constants, bulk modulus, and Debye temperatures are in good agreement with experimental data. Finally, the pressure dependence of the theoretical elastic constants and elastic modulus of LaS has been studied. The observations show that LaS is mechanically stable not only in B₁ phase below 8.77 GPa but also in B₂ phase under high pressure. LaS is ductile in B₁ phase while brittle in B₂ phase. The present observation of physical properties in B₂ phase of LaS needs validation by future experimental.     

Pressure dependence of elastic properties of ZnX (X = Se,S and Te): Role of charge transfer

An effective interaction potential (EIOP) is developed to invoke the pressure induced phase transition from zinc blende (B3) to rocksalt (B1) structure and anharmonic properties in ZnX (X = Se, S, Te) semiconductors. The effective interaction potential incorporates the long range Coulomb interaction, van der Waals interaction and short-range repulsive interaction up to second neighbour ions within the Hafemeister and Flygare approach as well as the charge transfer effects caused by the electron-shell deformation of the overlapping ions. The van der Waals coefficients are computed by the Slater Kirkwood variation method as a first step. Later on, we evaluate volume collapse, second order and third order elastic constants with pressure pointing to the systematic trends in all compounds of zinc blende structure and their thermal properties such as force constant, Gruneisen parameter, compressibility, Debye temperature etc. The vast volume discontinuity in pressure-volume (PV) phase diagram identifies the structural phase transition from zinc blende (B3) to rock salt (B1) structure and is consistent with those revealed from earlier reports.     

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.     

Elastic constants and high pressure structural transitions in yttrium pnictides

We present first-principles calculations on the structural, elastic and high pressure properties of yttrium pnictide compounds, using the pseudo-potential plane-waves approach based on density functional theory, within the generalized gradient approximation. Results are given for lattice constant, bulk modulus and its pressure derivative. The pressure transition at which these compounds undergo structural phase transition from NaCl-type (B1) to CsCl-type (B2) structure is calculated and compared with previous calculations and available experimental data. The elastic constants and their pressure dependence are calculated using the static finite strain technique. We derived the bulk and shear moduli, Young’s modulus and Poisson’s ratio of the B1 phase for YN, YP, YAs and YSb compounds. We estimated the Debye temperature of these compounds from the average sound velocity. This is the first quantitative theoretical prediction of the elastic properties of YN, YP, YAs and YSb compounds, and it still awaits experimental confirmation.     

Mechanical properties of hybrid composites using finite element method based micromechanics

A micromechanical analysis of the representative volume element of a unidirectional hybrid composite is performed using finite element method. The fibers are assumed to be circular and packed in a hexagonal array. The effects of volume fractions of the two different fibers used and also their relative locations within the unit cell are studied. Analytical results are obtained for all the elastic constants. Modified Halpin–Tsai equations are proposed for predicting the transverse and shear moduli of hybrid composites. Variability in mechanical properties due to different locations of the two fibers for the same volume fractions was studied. It is found that the variability in elastic constants and longitudinal strength properties was negligible. However, there was significant variability in the transverse strength properties. The results for hybrid composites are compared with single fiber composites.     

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.     

大跨度桥梁典型断面颤振机理

该文建立了箱梁表面压力与颤振导数之间的数学关系,探讨了表面压力的分布特性对箱梁颤振导数和颤振临界风速的影响。结合流固松耦合的计算方法,利用动网格技术模拟了箱梁的风致振动。采用分块分析方法研究了箱梁表面压力的局部特性对颤振导数以及系统振动能量的影响。研究结果表明：箱梁迎风侧风嘴附近的分布压力对模型振动的稳定性产生了不利的影响,而模型尾部的压力则有助于提高系统的颤振临界风速。当迎风侧的分布压力向模型尾部移动时,对箱梁颤振稳定性影响较大的颤振导数则会发生较显著的变化,箱梁的颤振临界风速也随之增加,因此断面迎风侧风嘴附近区域的分布压力对颤振导数和系统振动的稳定性影响最大。另外,迎风侧风嘴附近的区域也是振动系统吸收气动能量的主要部位,而箱梁尾部风嘴附近的区域则消耗系统的振动能量。箱梁表面压力与模型振动最大位移之间的相位差对颤振导数有较大影响,当相位差沿断面呈反对称分布,并使气动阻尼始终为负时,则有利于箱梁颤振的稳定性。     

箱梁表面的压力分布对颤振稳定性的影响EI北大核心CSCD

该文建立了箱梁表面压力与颤振导数之间的数学关系,探讨了表面压力的分布特性对箱梁颤振导数和颤振临界风速的影响。结合流固松耦合的计算方法,利用动网格技术模拟了箱梁的风致振动。采用分块分析方法研究了箱梁表面压力的局部特性对颤振导数以及系统振动能量的影响。研究结果表明:箱梁迎风侧风嘴附近的分布压力对模型振动的稳定性产生了不利的影响,而模型尾部的压力则有助于提高系统的颤振临界风速。当迎风侧的分布压力向模型尾部移动时,对箱梁颤振稳定性影响较大的颤振导数则会发生较显著的变化,箱梁的颤振临界风速也随之增加,因此断面迎风侧风嘴附近区域的分布压力对颤振导数和系统振动的稳定性影响最大。另外,迎风侧风嘴附近的区域也是振动系统吸收气动能量的主要部位,而箱梁尾部风嘴附近的区域则消耗系统的振动能量。箱梁表面压力与模型振动最大位移之间的相位差对颤振导数有较大影响,当相位差沿断面呈反对称分布,并使气动阻尼始终为负时,则有利于箱梁颤振的稳定性。