金属结合能、线膨胀系数及德拜温度的解析研究与计算

采用两体势模型研究了7类晶系共53种金属的结合能、线膨胀系数及德拜温度,并给出了三者之间普适性的关联方程及解析计算式.理论计算出的线膨胀系数及德拜温度与实验值比较其平均相对误差分别为2.9%和1.66%,相对均方根误差分别为3.75%和2.19%.金属结合能、线膨胀系数及德拜温度三者关联方程中,存在适合于不同晶系结构的共同的关联因子,该因子的均值为1.046,相对均方根误差为2.17%.     

由微观参量表示的金属单晶体杨氏模量的解析计算式

根据原子物理晶体模型 ,采用原子间相互作用的势函数分析方法 ,得到了由微观物理量表示的金属单晶体杨氏模量的解析计算式 .计算了 7种金属晶体的杨氏模量及金属晶体的断裂强度 ,计算结果与实际值吻合很好 .     

铟钇金属间化合物力学性能的第一性原理计算

本文基于密度泛函理论的平面波超软赝势方法,对铟钇(In-Y)金属间化合物的力学结构稳定性、弹性性质和热力学性能进行了研究.通过结构优化得到了In_3Y、InY、InY_2三种金属间化合物的晶格常数,发现与实验值比较吻合.弹性常数的计算结果表明In-Y金属间化合物的结构是稳定的,由弹性常数推算出In_3Y、InY、InY_2三种合金的体积模量、杨氏模量、剪切模量、泊松比和各向异性等力学性质,发现InY_2合金的体积模量、杨氏模量、剪切模量要比其它两种的值大,其抗形变能力更强.本文还预测了In-Y金属间化合物的热力学性质,如德拜温度、热导率,通过第一性原理计算得到的In-Y金属间化合物的力学和热力学性质为In-Y合金材料的实际应用和材料设计提供了参考.     

高温高压下Zr2AlC的结构及热学性质的第一性原理

利用密度泛函理论研究了高温高压下Zr₂AlC的结构和热力学性质,计算得到Zr₂AlC的晶格参数与实验值符合较好．研究了Zr₂AlC的弹性常数、体模量、剪切模量和杨氏模量等力学性质随压力变化的趋势．同时研究了维氏硬度随压力的变化趋势．通过计算得到的杨氏模量预测了Zr₂AlC的弹性各向异性．最后,基于准简谐德拜模型,成功预测了Zr₂AlC的德拜温度、热容、热膨胀系数和Grüneisen参数随着压强和温度的变化关系.     

硅酸镁钙钛矿弹性及热力学特性的第一性原理计算

基于密度泛函理论的第一性原理计算,结合准谐德拜模型研究了高压下硅酸镁钙钛矿的弹性及热力学特性. 计算得到的物态方程数据、热容、热膨胀系数等在宽广的温度和压力范围与实验结果及其他理论计算结果吻合. 根据有限应变理论计算了硅酸镁钙钛矿的弹性常数,并讨论了杨氏模量、泊松比、德拜温度、晶体各向异性随压力的变化.     

点缺陷对 L12-Al3Li金属间化合物热力学性能的影响

运用基于第一性原理的平面波赝势法研究了L12-Al3Li金属间化合物中Li原子空位和Al原子反位缺陷对Al3Li热力学性能的影响,结果表明：Al反位缺陷易与周围原子形成局域共价键,使晶体体积增大,而Li空位缺陷却减小了晶体体积。Li空位缺陷使L12-Al3Li的硬度增加,延展性降低,德拜温度值升高。Al反位缺陷降低了晶体的硬度,增加了延展性,降低了德拜温度值。在德拜温度以下,Li空位缺陷减小了L12-Al3Li的热容, 而Al反位缺陷使晶体热容增大。晶格畸变对L12-Al3Li晶体的热力学性能有重要影响     

点缺陷对L1_2-Al_3Li金属间化合物热力学性能的影响

运用基于第一性原理的平面波赝势法研究了L12-Al3Li金属间化合物中Li原子空位和Al原子反位缺陷对Al3Li热力学性能的影响,结果表明:Al反位缺陷易与周围原子形成局域共价键,使晶体体积增大,而Li空位缺陷却减小了晶体体积.Li空位缺陷使L12-Al3Li的硬度增加,延展性降低,德拜温度值升高.Al反位缺陷降低了晶体的硬度,增加了延展性,降低了德拜温度值.在德拜温度以下,Li空位缺陷减小了L12-Al3Li的热容,而Al反位缺陷使晶体热容增大.晶格畸变对L12-Al3Li晶体的热力学性能有重要影响.     

温度和压强对金属化合物Co_2Zr和Co_2Ti的结构和热力学性质影响的研究

基于平面波赝势密度泛函理论(DFT)和广义梯度近似(GGA)的第一性原理计算了高温高压下金属化合物Co_2Zr和Co_2Ti的结构和热力学性质.Co_2Zr和Co_2Ti均为立方晶体,且结构类型为Cu2Mg结构.通过计算得出的晶格参数跟实验值符合较好.用准谐德拜模型计算了Co_2Zr和Co_2Ti的热力学性质.在0~100 GPa的压强和0~1500 K的温度作用下,两种物质的德拜温度Θ,热容CV,热膨胀系数α随压强和温度的变化而变化.随着压强的增大,德拜温度单调的增加;相同压强下,Co_2Ti的德拜温度始终大于Co_2Zr.热容CV和热膨胀系数α均随温度的增加而增加,增大压强时反而减小,说明减小温度和增大压强对CV以及α有相同的影响.     

高压下超导体YBa_2Cu_3O_7弹性性质的第一性原理研究(英文)

通过从头算密度泛函理论研究了YBa2Cu3O7的结构和弹性性质.发现c轴最容易压缩.另外,我们还计算了各种弹性性质与压强的关系,例如弹性模量,剪切模量,杨氏模量,泊松比.最后,我们获得了不同压强下的德拜温度和声速.     

高压下超导体YBa2Cu3O7弹性性质的第一性原理研究

通过从头算密度泛函理论研究了YBa2Cu3O7的结构和弹性性质。发现c轴最容易压缩。另外,我们还计算了各种弹性性质与压强的关系,例如弹性模量,剪切模量,杨氏模量,泊松比。最后,我们获得了不同压强下的德拜温度和声速。     

Ab initio studies of the structural,elastic, electronic and thermal properties of NiTi2 intermetallic

First principles calculations were performed in the framework of the density functional theory (DFT) using the Full Potential–Linear Augment Plane Wave method (FP–LAPW) within the generalized gradient approximation (GGA) to predict the structural, electronic, elastic and thermal properties of NiTi₂ intermetallic compound. By using the Wien2k all-electron code, calculations of the ground state and electronic properties such as lattice constants, bulk modulus, presure derivative of bulk modulus, total energies and density of states were also included. The elastic constants and mechanical properties such as Poisson’s ratio, Young’s modulus and shear modulus are estimated from the calculated elastic constants of the single crystal. Through the quasi-harmonic Debye model, the preasure and temperature dependences of the linear expansion coefficient, bulk modulus and heat capacity have been investigated. Finally, the Debye temperature has been estimated from the average sound velocity according to the predicted polycrystal bulk properties and from the single crystal elastic constants.     

FP-LMTO calculations of the structural,elastic, thermodynamic,and electronic properties of the ideal-cubic perovskite BiGaO3

Using the first-principles full-potential linear muffin-tin orbital method within the local density approximation, we have studied the structural, elastic, thermodynamic, and electronic properties of the ideal-cubic perovskite BiGaO₃. It is found that this compound has an indirect band gap. The valence band maximum (VBM) is located at Γ-point, whereas the conduction band minimum (CBM) is located at X-point. The pressure and volume dependences of the energy band gaps have been calculated. The elastic constants at equilibrium are also determined. We derived the bulk and shear moduli, Young’s modulus, and Poisson’s ratio. The thermodynamic properties are predicted through the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. The variation of the bulk modulus, heat capacities, and Debye temperature with pressure and temperature are successfully obtained.     

Dependence of electrical and magnetic properties of the AuCu-1 alloy on its atomic ordering

Electrical resistivity and magnetic susceptibility studies have shown that atomic ordering in theα ₁ phase of the AuCu-1 alloy is accompanied by a decrease in the Fermi energy, in the Debye characteristic temperature, and in the Young modulus. The behavior of conduction electrons in the ordered AuCu-1 alloy is appreciably affected by the interaction of such electrons with ions in the crystal lattice.     

Alpha-plutonium's polycrystalline elastic moduli over its full temperature range

alpha-plutonium's volume-corrected polycrystal elastic moduli were measured between 18 K and the upper limit of its occurrence, near 400 K. The two independent moduli for a polycrystal-bulk and shear-behave smoothly, indicating no phase transition. Both moduli show the same 50% increase on cooling, an order of magnitude larger than in other metals. The Debye temperature obtained from low-temperature elastic moduli, 207 K, significantly exceeds most previous estimates. The Gruneisen parameter gamma=5.3, obtained from the temperature dependence of the bulk modulus, is intermediate among previous estimates using other approaches, alpha-plutonium's Poisson ratio nu is low: 0.18, nearly temperature independent, and its small decrease on warming opposes usual behavior. The high gamma, large but equal bulk modulus and shear modulus fractional stiffening on cooling, and near-temperature-invariant nu are attributed to a single mechanism: 5-f electron localization-delocalization.     

Recovery of Young’s modulus upon annealing of nanostructured niobium produced through severe plastic deformation

The effect of temperature (in the range 20–500°C) on the Young’s modulus of nanostructured niobium with Ta impurity content <0.5 wt % and that of O₂ < 0.1 wt % and with a mean grain size of ?200 nm is studied. The transformation of polycrystalline niobium into a nanostructured state is performed through severe plastic deformation by equal-channel angular pressing. The Young’s modulus is found to increase in two stages as the temperature of isothermal annealing is gradually increased. The mechanisms of recovery of the elastic modulus upon annealing of the nanostructured niobium are discussed in the context of the modern concepts of the defect structure of deformed metals.     

First-principles investigations on structural,elastic, electronic properties and Debye temperature of orthorhombic Ni3Ta under pressure

The structural, elastic, electronic properties and Debye temperature of Ni₃Ta under different pressures are investigated using the first-principles method based on density functional theory. Our calculated equilibrium lattice parameters at 0 GPa well agree with the experimental and previous theoretical results. The calculated negative formation enthalpies and elastic constants both indicate that Ni₃Ta is stable under different pressures. The bulk modulus B, shear modulus G, Young’s modulus E and Poisson’s ratio ν are calculated by the Voigt–Reuss–Hill method. The bigger ratio of B/G indicates Ni₃Ta is ductile and the pressure can improve the ductility of Ni₃Ta. In addition, the results of density of states and the charge density difference show that the stability of Ni₃Ta is improved by the increasing pressure. The Debye temperature Θ _D calculated from elastic modulus increases along with the pressure.     

Elastic and thermodynamical properties of A15 Nb3X (X = Al,Ga, In,Sn and Sb) compounds — First principles DFT study

Elastic and thermodynamical properties of Nb₃X (X = Al, Ga, In, Sn and Sb) compounds are obtained by performing the band structure calculations, using the FP-LAPW method. The calculated lattice constants, elastic constants, Bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, Debye temperature and anisotropy ratio are reported and the results agree with the available data. From the present study, it is observed that stiffness and shear resistance are found to be greater in Nb₃Sb than in other compounds. It is more brittle in nature and comparatively harder than other materials under study. The degree of anisotropy decreases as one moves across Nb₃Ga, Nb₃Al, Nb₃In, Nb₃Sb and Nb₃Sn. From the calculated values of the Debye temperature, it is observed that thermal conductivity is greater for Nb₃Sb and less for Nb₃In.     

A first-principles study on structural stability and mechanical properties of polar intermetallic phases CaZn2 and SrZn2

Structural stability and electronic properties of polar intermetallic CaZn₂ and SrZn₂ in both CeCu₂-type and MgZn₂-type structures have been investigated using first-principles method. The calculated equilibrium lattice parameters agree closely with the available experimental and other theoretical results. In terms of formation enthalpy, it is discovered that the present compounds with CeCu₂-type structure are energetically more stable than that with MgZn₂-type. They are all mechanically stable according to the criteria of elastic stability. In particular, we have investigated the pressure effect on the compressive behaviour and structural stability of each compound. Subsequently, the bulk modulus, shear modulus, Young’s modulus, theoretical hardness, Poisson’s ratio and Debye temperature in the ground state can be estimated using Voigt–Reuss–Hill homogenization method. Mechanical anisotropy is characterized by the anisotropic factors and direction-dependent Young’s modulus. Finally, the electronic structures are determined to reveal the bonding characteristics of considered phases.     

Theoretical investigations of the physical properties of tetragonal CaSiO3 perovskite

The first principles study of the physical properties of tetragonal CaSiO₃ perovskite is reported using the pseudopotential plane wave method within the local density approximation. The calculated equilibrium volume is in good agreement with the available experimental data. A complete elastic tensor of the tetragonal CaSiO₃ perovskite is determined in the wide pressure range. The geologically important quantities: sound velocity, Young’s modulus, Poisson’s ratio, and crystal anisotropy, are derived from the calculated data. A systematic decrease of crystal’s anisotropy with pressure is noticed except symmetry plane (001). Finally, by using a quasiharmonic Debye model, the Debye temperature, the heat capacity, the coefficient of thermal expansion, and the Grüneisen parameter are also obtained in the present work.     

Ab initio investigation of the structural,elastic and electronic properties of the anti-perovskite TlNCa3

We have investigated the structural, elastic and electronic properties of the anti-perovskite TlNCa₃ using ab initio calculations within the generalized gradient approximation and the local density approximation for the exchange–correlation potential. The lattice constant, bulk modulus, elastic constants and their pressure dependence, energy band structures, density of states and charge density distribution are calculated and analyzed in comparison with the available experimental and theoretical data. The bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, Lamé’s coefficients, average sound velocity and Debye temperature are numerically estimated for ideal polycrystalline TlNCa₃ aggregates in the framework of the Voigt–Reuss–Hill approximation. This is the first theoretical prediction of the elastic constants and their related properties for TlNCa₃ that requires experimental confirmation.