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1.
《中国物理快报》2016,(3)
Using the newly developed particle swarm optimization algorithm on crystal structural prediction,we predict a new class of boron nitride with stoichiometry of NB_2 at ambient pressure,which belongs to the tetragonal I4m2 space group.Then,its structure,elastic properties,electronic structure,and chemical bonding are investigated by first-principles calculations with the density functional theory.The phonon calculation and elastic constants confirm that the predicted NB_2 is dynamically and mechanically stable,respectively.The large bulk modulus,large shear modulus,large Young's modulus,and small Poisson's ratio show that the I4m2 NB_2 should be a new superhard material with a calculated theoretical Vickers hardness value of 66 GPa.Further analysis on density of states and eiectron localization function demonstrate that the strong B-B and B-N covalent bonds are the main reason for its high hardness in I4m2 NB_2. 相似文献
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Structural, thermodynamic and electronic properties of zinc-blende AlN from first-principles calculations 下载免费PDF全文
Structural, thermodynamic and electronic properties of zinc-blende
AlN under pressure are investigated by first-principles calculations
based on the plane-wave basis set. Through the analysis of enthalpy
variation of AlN in the zinc-blende (ZB) and the rock-salt (RS)
structures with pressure, we find the phase transition of AlN from
ZB to RS structure occurs at 6.7 GPa. By using the quasi-harmonic
Debye model, we obtain the heat capacity CV, Debye temperature
ΘD, Grüneisen parameter γ and thermal
expansion coefficient α. The electronic properties including
fundamental energy gaps and hydrostatic deformation potentials are
investigated and the dependence of energy gaps on pressure is
analysed. 相似文献
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In recent years, transition metal borides (TMBs) have attracted much attention because they are considered as potential superhard materials and have more abundant crystal structures compared with traditional superhard materials. So far, however, no superhard materials have been found in TMBs. A large number of structures and potential new properties in TMBs are induced by the various hybridization ways of boron atoms and the high valence electrons of transition metals, which provide many possibilities for its application. And most TMBs have layered structures, which make TMBs have the potential to be a two-dimensional (2D) material. The 2D materials have novel properties, but the research on 2D TMBs is still nearly blank. In this paper, the research progress of TMBs is summarized involving structure, mechanical properties, and multifunctional properties. The strong covalent bonds of boron atoms in TMBs can form one-dimensional, two-dimensional, and three-dimensional substructures, and the multiple electron transfer between transition metal and boron leads to a variety of chemical bonds in TMBs, which are the keys to obtain high hardness and multifunctional properties of TMBs. Further research on the multifunctional properties of TMBs, such as superconductors, catalysts, and high hardness ferromagnetic materials, is of great significance to the discovery of new multifunctional hard materials. 相似文献
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在广义梯度近似(GGA)和GGA+U(在位库仑势)下,采用第一性原理方法系统地研究了三元过渡金属硼碳化合物YPd3X(X=B,C)的晶体结构、弹性性质、电子结构和成键特性.计算的晶格参数和体弹性模量均与报道的实验结果吻合,而YPd3X(X=B,C) 的弹性参数计算值则表明YPd3C的硬度大于YPd3B.根据晶体机械稳定标准得到YPd3B和YPd3C的失稳临界压强分别约为16.5GPa和23GPa.由Pugh经验关系可知YPd3X(X=B,C)均属于韧性材料,且YPd3B的韧性略高于YPd3C.电子能带结构分析表明YPd3B和YPd3C均具有金属特性,且导电能力相当.由态密度和电荷密度分析得知,X与Pd之间形成较强的共价键,而Y与Pd3X之间形成离子键,化学键键能的不同是两种材料的弹性参数存在差异的内在原因.上述的研究结果为YPd3X(X=B,C)的力电材料的设计和应用提供了一定的理论依据. 相似文献
5.
A new transition metal diphosphide α-MoP2 synthesized by a high-temperature and high-pressure technique 下载免费PDF全文
Xiaolei Liu 《中国物理 B》2023,32(1):18102-018102
Monoclinic $\alpha $-MoP$_{2}$, with the OsGe$_{2}$-type structure (space group $C2/m$, $Z = 4$) and lattice parameters $a = 8.7248(11) $ Å, $b = 3.2322(4) $ Å, $c = 7.4724(9) $ Å, and $\beta =119.263^\circ $, was synthesized under a pressure of 4 GPa at a temperature between 1100 ${^\circ}$C and 1200 ${^\circ}$C. The structure of $\alpha $-MoP$_{2}$ and its relationship to other transition metal diphosphides are discussed. Surprisingly, the ambient pressure phase orthorhombic $\beta $-MoP$_{2}$ (space group Cmc2$_{1}$) is denser in structure than $\alpha $-MoP$_{2}$. Room-temperature high-pressure x-ray diffraction studies exclude the possibility of phase transition from $\beta $-MoP$_{2}$ to $\alpha $-MoP$_{2}$, suggesting that $\alpha $-MoP$_{2}$ is a stable phase at ambient conditions; this is also supported by the total energy and phonon calculations. 相似文献
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基于密度泛函理论平面赝势波法的第一性原理计算,研究过渡金属单硼化物TMB(以3d系列中的TiB、VB和CrB;4d系列中的ZrB、NbB和MoB;5d系列中的HfB、TaB和WB为例)的热力学稳定性、力学性质和微观机制.发现过渡金属单硼化物的热力学稳定与硬度异常的规律.当价电子浓度为8 e·(f.u.)-1时,热力学最稳定,且硬度最高.计算TMB的电子结构,发现TMB的价电子浓度为8 e·(f.u.)-1时,pd共价键合,有效阻碍了金属双层之间的位错滑动,防止剪切变形,致使其具有高硬度. 相似文献
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First-principles investigations on elastic and thermodynamic properties of zinc-blende structure BeS 下载免费PDF全文
In this paper the elastic and thermodynamic properties of the cubic
zinc-blende structure BeS at different pressures and temperatures
are investigated by using \textit{ab initio} plane-wave
pseudopotential density functional theory method within the
generalized gradient approximation (GGA). The calculated results are
in excellent agreement with the available experimental data and
other theoretical results. It is found that the zinc-blende
structure BeS should be unstable above 60GPa. The thermodynamic
properties of the zinc-blende structure BeS are predicted by using
the quasi-harmonic Debye model. The pressure-volume-temperature
($P-V-T$) relationship, the variations of the thermal expansion
coefficient $\alpha$ and the heat capacity $C_{V}$ with pressure $P$
and temperature $T$, as well as the Gr\"{u}neisen
parameter-pressure-temperature ($\gamma -P-T$) relationship are
obtained systematically in the ranges of 0--90GPa and 0--2000K. 相似文献
12.
采用密度泛函理论中的赝势平面波方法系统地研究了高压下RhB的结构相变、弹性性质、电子结构和硬度.分析表明,RhB在25.3 GPa时从anti-NiAs结构相变到FeB结构,这两种结构的弹性常数、体弹模量、剪切模量、杨氏模量和弹性各向异性因子的外压力效应明显.电子态密度的计算结果显示,这两种结构是金属性的,且费米能级附近的峰随着压强的增大向两侧移动,赝能隙变宽,轨道杂化增强,共价性增强,非局域化更加明显.此外,硬度计算结果显示,anti-NiAs-RhB的金属性比较弱,有着较高的硬度,属于硬质材料. 相似文献
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Based on the first-principles plane-wave basis pseudopotential calculations, we investigate mechanical properties and electronic structures of the hardest known oxide, cotunnite TiO2. The calculated results show that cotunnite TiO2 has the highest bulk modulus (348 GPa) and hardness (32 GPa) among the high-pressure phases of TiO2, but its mechanical properties are not superior to those of c-BN. Moreover, the high hardness of cotunnite TiO2 can be understood from both the dense crystal structure (high valence electron density and short bond lengths) and the unusual mixtures of covalent and ionic bonding of Ti-O. 相似文献
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Novel structures and mechanical properties of Zr2N:Ab initio description under high pressures 下载免费PDF全文
With the formation of structural vacancies,zirconium nitrides(key materials for cutting coatings,super wearresistance,and thermal barrier coatings) display a variety of compositions and phases featuring both cation and nitrogen enrichment.This study presents a systematic exploration of the stable crystal structures of zirconium heminitride combining the evolutionary algorithm method and ab initio density functional theory calculations at pressures of 0 GPa,30 GPa,60 GPa,90 GPa,120 GPa,150 GPa,and 200 GPa.In addition to the previously proposed phases P42/mnm-,Pnnn-,and Cmcm-Zr2 N,five new high-pressure Zr2N phases of PA/nmm,IA/mcm,P21/m,P3 m1,and C2/m are discovered.An enthalpy study of these candidate configurations reveals various structural phase transformations of Zr2 N under pressure.By calculating the elastic constants and phonon dispersion,the mechanical and dynamical stabilities of all predicted structures are examined at ambient and high pressures.To understand the structure-property relationships,the mechanical properties of all Zr2N compounds are investigated,including the elastic moduli,Vickers hardness,and directional dependence of Young’s modulus.The Cmncm-Zr2 N phase is found to belong to the brittle materials and has the highest Vickers hardness(12.9 GPa) among all candidate phases,while the I4/mcm-Zr2 N phase is the most ductile and has the lowest Vickers hardness(2.1 GPa).Furthermore,the electronic mechanism underlying the diverse mechanical behaviors of Zr2 N structures is discussed by analyzing the partial density of states. 相似文献
15.
High-pressure Raman study of osmium and rhenium up to 200 GPa and pressure dependent elastic shear modulus C44 下载免费PDF全文
Jingyi Liu 《中国物理 B》2022,31(3):37801-037801
High-pressure Raman scattering from hexagonal close-packed (HCP) metals Os and Re have been extended up to 200 GPa, and the pressure-dependent shear modulus C44 has been deduced from the Raman-active mode E2g, which is generated from the adjacent vibration of atoms in hexagonal planes, providing the valuable information about the elastic properties for HCP metals under high pressure. Combined with the available data of HCP metals from previous works, a further study indicates that the $C_{44}^\prime/C_{44}$ ratio would be close to a constant value, 0.01, with increasing atomic number of metals. The results obtained from high-pressure Raman scattering will allow us to probe the elastic anisotropy of the HCP metals at very high pressure. 相似文献
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Molecular dynamics simulation is employed to study the structural evolution of low density amorphous ice during its compression from one atmosphere to 2.5 GPa. Calculated results show that high density amorphous ice is formed at an intermediate pressure of -1.0 GPa; the O-O-O bond angle ranges from 83° to 113°, and the O-H… O bond is bent from 112° to 160°. Very high density amorphous ice is obtained by quenching to 80 K and decompressing the ice to ambient pressure from 160 K/1.3 GPa or 160 K/1.7 GPa; and the next-nearest O-O length is found to be 0.310 nm, just 0.035 nm beyond the nearest O-O distance of 0.275 nm. 相似文献
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Three of the five structures obtained from the evolutionary algorithm based structure search of Ruthenium Carbide systems in the stoichiometries RuC, Ru2C and Ru3C are relaxed at different pressures in the range 0–200 GPa and the pressure-induced variation of their structural, elastic, dynamical, electronic and thermodynamic properties as well as hardness is investigated in detail. No structural transition is present for these systems in this pressure range. RuC–Zinc blende is mechanically and dynamically unstable close to 100 GPa. RuC-Rhombohedral and Ru3C-Hexagonal retain mechanical and dynamical stability up to 200 GPa. For all three systems the electronic bands and density of states spread out with pressure and the band gap increases with pressure for the semiconducting RuC–Zinc blende. From the computed IR spectrum of RuC–Zinc blende at 50 GPa it is noted that the IR frequency increases with pressure. Using a semi-empirical model for hardness it is estimated that hardness of all three systems consistently increases with pressure. The hardness of RuC–Zinc blende increases towards the superhard regime up to the limiting pressure of its mechanical stability while that of RuC-Rhombohedral becomes 30 GPa at the pressure of 150 GPa. 相似文献
18.
B. Abidri D. Rached H. Baltache I. Merzoug 《Journal of Physics and Chemistry of Solids》2010,71(12):1780-1784
We present in this paper the results of an ab initio theoretical study within the local density approximation (LDA) to determine in rock-salt (B1), cesium chloride (B2), zinc-blende (B3), and tungsten carbide (WC) type structures, the structural, elastic constants, hardness properties and high-pressure phase of the noble metal carbide of ruthenium carbide (RuC).The ground state properties such as the equilibrium lattice constant, elastic constant, the bulk modulus, its pressure derivative, and the hardness in the four phases are determined and compared with available theoretical data. Only for the three phases B1, B3, and WC, is the RuC mechanically stable, while in the B2 phase it is unstable, but in B3 RuC is the most energetically favourable phase with the bulk modulus 263 GPa, and at sufficiently high pressure (Pt=19.2 GPa) the tungsten carbide (WC) structure would be favoured, where ReC-WC is meta-stable.The highest bulk modulus values in the B3, B2, and WC structures and the hardnesses of H(B3)=36.94 GPa, H(B1)=25.21 GPa, and H(WC)=25.30 GPa indicate that the RuC compound is a superhard material in B3, and is not superhard in B1 and WC structures compared with the H(diamond)=96 GPa. 相似文献
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本论文中, 采用晶体结构预测软件USPEX结合第一性原理方法全面地搜索了Hf-C体系在高压下的晶体结构, 预测得到了两种新的化合物及HfC在高压下的相变路径. 压力低于100 GPa 时, 除了常压下的结构HfC, Hf3C2, Hf6C5, 并没有得到新的热力学稳定结构. 在200 GPa时, 预测得到了一种新化合物——Hf2C, 空间群为I4/m; 且HfC的结构发生了相变, 空间群由Fm3m变为C2/m. 在300 GPa时, 预测得到了另一种新化合物——HfC2, 空间群为Immm. 而在400 GPa时, HfC的结构再次发生相变, 空间群为Pnma. 通过能量计算, 得到了Hf-C体系的组分-压力相图: 在压力分别低于15.5 GPa和37.7 GPa时, Hf3C2和Hf6C5是稳定的; 压力分别大于102.5 GPa和215.5 GPa时, Hf2C和HfC2变成稳定化合物; HfC的相变路径为Fm3m→C2/m→Pnma, 相变压力分别为185.5 GPa 和322 GPa. 经结构优化后, 得到了这四种高压新结构的晶体学数据, 如晶格常数、原子位置等, 并分析了其结构特点. 对于Hf-C 体系中的高压热力学稳定结构, 分别计算了其弹性性质和声子谱曲线, 证明是力学稳定和晶格动力学稳定的. 采用第一性原理软件VASP模拟高压结构的能带结构、态密度、电子局域函数和Bader 电荷分析, 发现HfC(C2/m, Pnma结构), Hf2C 和HfC2 中Hf-C 键具有强共价性、弱金属性和离子性, 且C-C 间存在共价作用. 相似文献