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1.
The constants of the central and noncentral interactions between carbon atoms in 2D supracrystals, i.e., generalized two-dimensional crystals in which the sites of the lattice contain, instead of individual atoms, their symmetric complexes, have been calculated. It has been shown that these constants essentially depend on the symmetry of the 2D supracrystal and can significantly differ from the corresponding constants for graphene.  相似文献   

2.
研究了用缓慢升温法生长的α-AlPO4晶体的弹性温度特性。测量采用传输法,测温范围为-30—150℃;用最小二乘法拟合弹性-温度曲线;用电子计算机处理数据。给出了弹性常数cij和sij(i,j=1,2,…,6)的温度特性方程以及T0=25℃时的一级、二级和三级温度系数。 关键词:  相似文献   

3.
The linear and nonlinear elastic properties of B4C boron carbide ceramics have been studied. The second-order elastic constants and other parameters of the theory of elasticity in the linear approximation have been calculated based on the experimentally measured density and velocity values of longitudinal and shear bulk acoustic waves in the samples. The Thurston-Brugger method has been used to determine the third-order elastic constants of B4C. To achieve this, we have measured the relative changes of the longitudinal and shear bulk acoustic wave velocities depending on the uniaxial compression applied to the sample.  相似文献   

4.
Elastic properties of NaClO3, KClO3, LiClO4, NaClO4, and KClO4 have been investigated from first principles by the method of linear combination of atomic orbitals in the gradient approximation of the density functional theory using CRYSTAL software. The elastic constants and moduli, hardness, Poisson’s ratio, and the anisotropy parameters have been calculated. The velocities of sound, the Debye temperature, the thermal conductivity, and the Grüneisen parameter have been estimated. It has been found that these compounds are mechanically stable, anisotropic, and ductile materials. The dependences of their elastic parameters on the atomic number of the cation have been calculated. The obtained results are in good agreement with the available experimental data.  相似文献   

5.
The lattice dynamics, second and third order elastic constants and the lattice thermal expansion of dysprosium have been calculated using Keating's approach. The ten third order elastic constants are calculated using four anharmonic parameters. The present model reproduces the measured pressure derivatives of the second order elastic constants of dysprosium well. The low and high temperature limits γ?I and γ?H of the lattice thermal expansion are evaluated and the agreement between the calculated γ?H and that obtained from the thermal expansion and specific heat data is satisfactory.  相似文献   

6.
The optical and acoustic properties of tellurite glasses in the system TeO2/ZrO2/WO3 have been investigated. The refractive index at different wavelengths and the optical spectra of the glasses have been measured. From the refractive index and absorption edge studies for prepared glasses, the optical parameter viz; optical band gap (Eopt), Urbach energy, (ΔE), dispersion energy, Ed, and the average oscillator energy, E0, have been calculated. Sound velocities were measured by pulse echo technique. From these velocities and densities values, various elastic moduli were calculated. The variations in the refractive index, optical energy gap and elastic moduli with WO3 content have been discussed in terms of the glass structure. Quantitatively, we used the bond compression model for analyzing the room temperature elastic moduli data. By calculating the number of bonds per unit volume, the average stretching force constant, and the average ring size we can extract valuable information about the structure of the present glasses.  相似文献   

7.
First-principles calculations of the crystal structure and the elastic properties of OsN2 have been carried out with the plane-wave pseudopotential density functional theory method. The calculated values are in very good agreement with experimental data as well as with some of the existing model calculations. The dependence of the elastic constants cij, the aggregate elastic moduli (B,G,E), Poisson’s ratio, and the elastic anisotropy on pressure has been investigated. Moreover, the variation of the Debye temperature and the compressional and shear elastic wave velocities with pressure P up to 60 GPa at 0 K have been investigated for the first time.  相似文献   

8.
Yildirim A  Koc H  Deligoz E 《中国物理 B》2012,21(3):37101-037101
The structural, elastic, electronic, optical, and vibrational properties of the orthorhombic Pd2Ga compound are investigated using the norm-conserving pseudopotentials within the local density approximation in the frame of density functional theory. The calculated lattice parameters have been compared with the experimental values and found to be in good agreement with these results. The second-order elastic constants and the other relevant quantities, such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocity, and Debye temperature, have been calculated. It is shown that this compound is mechanically stable after analysing the calculated elastic constants. Furthermore, the real and imaginary parts of the dielectric function and the optical constants, such as the optical dielectric constant and the effective number of electrons per unit cell, are calculated and presented. The phonon dispersion curves are derived using the direct method. The present results demonstrate that this compound is dynamically stable.  相似文献   

9.
K.R. Li  W. F. Lu  D. Şopu  B. Sarac  J.H. Yi 《哲学杂志》2020,100(7):874-893
ABSTRACT

The structural properties, enthalpies of formation and entropic temperatures of five stable Co-Zr intermetallics were systematically investigated by first-principles calculations. The calculated enthalpy of formation was used to measure the phase stability of the Co-Zr intermetallic compounds, and the results reveal that CoZr has the highest phase stability among these Co-Zr compounds. Considering the change of temperature, the entropic temperature TS was used to illustrate the high-temperature stability of the Co-Zr intermetallic compounds. Additionally, the elastic constants, anisotropy indexes and Debye temperatures have been calculated. According to the calculated anisotropy indexes, CoZr2 has the highest elastic anisotropy among the Co-Zr binary compounds. Furthermore, the bonding characteristics of these compounds have also been investigated by calculating the electronic structures.  相似文献   

10.
Elastic constants and bulk modulus for the tetragonal, rhombohedral, and cubic phase of Na0.5Bi0.5TiO3 crystal were calculated from the first principles. From the calculated elastic constants, other structural properties such as bulk modulus, shear modulus, Young's modulus, and Poisson's ratio can be derived using respective relationships from Voight–Reuss–Hill approximation; bulk modulus was calculated as an example in this article. It was shown that elastic constants show different behavior for compression and elongation. The different values of elastic constants have been calculated for the direction parallel to the bismuth layer (crystallographic a(b)-axis) and the perpendicular direction (crystallographic c-axis). It seems to be caused by bismuth layer structure oxides of Na0.5Bi0.5TiO3 crystal.  相似文献   

11.
Electronic structures, elastic properties and thermal stabilities of Mg17Al12, Mg2Si and Al2Y have been determined from first-principle calculations. The calculated heats of formation and cohesive energies show that Al2Y has the strongest alloying ability and structural stability. The brittle behavior and structural stability mechanism is also explained through the electronic structures of these intermetallic compounds. The elastic constants are calculated, the bulk moduli, shear moduli, Young's moduli and Poisson ratio value are derived, the brittleness and plasticity of these phases are discussed. Gibbs free energy, Debye temperature and heat capacity are calculated and discussed.  相似文献   

12.
The elastic properties of the compound family of the sulvanite Cu3TMX4 (TM=V, Nb, Ta; X=S, Se) have been calculated using first-principles total energy calculations within the density functional theory along with the local density and the generalized gradient approximations. The calculated elastic properties are the bulk modulus (B), the elastic constants (c11, c12 and c44), the Zener anisotropy factor (A), the isotropic shear modulus (G) and the Young modulus (E). By means of these quantities we have also computed other thermodynamic properties such as the average sound velocity (s) and the Debye temperature (ΘD). The calculated values of the elastic properties led to the conclusion that these compounds are brittle and fragile. We have also calculated the electron localization function, which exhibits the bonding characteristics in these compounds, showing that the Cu-X bond as well as the TM-X bond have a covalent character, but there is also present some ionicity in these compounds due to the Cu-TMX4 bond.  相似文献   

13.
The three independent second-order elastic constants and their temperature and pressure derivatives have been measured for four AgBr-AgCl mixed crystals, with 19.5, 39.1, 56.6 and 78.7 mole % AgCl, using the ultrasonic pulse-echo technique at room temperature. The explicit temperature dependence of the elastic constants is calculated and is found to be much larger than that of other NaCl structure crystals. The violation of the Cauchy relation C12 = C44 is found to be significant and increases between AgBr and AgCl. The high temperature limit of the Gruneisen parameter is calculated from the elastic data. A comparison is made between the elastic properties of the silver halides and the alkali halides.  相似文献   

14.
The structural, optical and elastic properties of cubic HfO2 were studied using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The ground-state properties such as lattice parameter and bulk modulus were calculated and these results are in favorable agreement with the previous work. The complex dielectric function, refractive index, extinction coefficient, complex conductivity function, energy-loss spectrum, absorption coefficient and optical reflectivity are calculated and the peak position distributions of imaginary parts of the complex dielectric function have been explained. The calculated elastic properties are consistent with other calculated results.  相似文献   

15.
The lattice constants, enthalpies of formation, elastic constants and electronic structures of Al-Sr intermetallics have been calculated by first-principles method within generalized gradient approximation. The calculated lattice constants and enthalpies of formation are in good agreement with experimental and other theoretical results. The polycrystalline bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio are also estimated from the calculated single crystalline elastic constants. The total and partial electronic densities of state for the intermetallics were obtained, and the results indicated that Al2Sr-oI is more stable than Al2Sr-cF. Finally, longitudinal, transverse and average sound velocities and Debye temperature are estimated.  相似文献   

16.
The electronic band structure and elastic constants of SnS2 and SnSe2 have been calculated by using density-functional theory (DFT). The calculated band structures show that SnS2 and SnSe2 are both indirect band gap semiconductors. The upper valence bands originate mainly from Sp and Snd electrons, while the lowest conduction bands are mainly from (S, Se) p and Sns states. The calculated elastic constants indicate that the bonding strength along the [100] and [010] direction is stronger than that along the [001] direction and the shear elastic properties of the (010) plane are anisotropic for SnS2 and SnSe2. Both compounds exhibit brittle behavior due to their low B/G ratio. Relationships among volumes, the heat capacity, thermal expansion coefficients, entropy, vibrational energy, internal energy, Gibbs energy and temperature at various pressures are also calculated by using the Debye mode in this work.  相似文献   

17.
Raman scattering measurements were performed on CeO2 nanoparticles at room temperature. Low-frequency modes are assigned to confined acoustic vibrations of spherical CeO2 nanoparticles. Frequencies of these vibrational modes have been calculated in the elastic continuum approximation, which considers a nanoparticle as a homogeneous elastic sphere. We assumed stress-free boundary conditions. The specific dependence of the vibrational frequency on the particle diameter enables the determination of the particle size from the experimental Raman frequency. The particle size value calculated in this way agrees well with the value acquired from the phonon confinement model. PACS 61.46.Df; 73.63.Bd; 63.22.+m  相似文献   

18.
In this work primarily structural parameters of the Y3Al2 was optimized. In the calculations, PBE type Exchange-Correlation function was selected in the GGA approximation and ultra-soft pseudopotential was used. Crystalline lattice parameters a = 15.581 Bohr, c / a = 0.923. Total energy was calculated by small deformations in volume. These values were fitted to the equation of state and the bulk modulus was calculated as 58.4 GPa. The working structure has elastic constants as C11, C12, C13, C33, C44 and C66. These constants have been calculated under ambient pressure. Using the elastic constants, bulk, shear, Young modulus and Poisson ratio (in Voigt approach) were obtained as 58.12, 34.31, 86.01 GPa and 0.25, respectively. Melting temperature of the material was guessed from the elastic constant. The results were compared with the current experimental and theoretical data.  相似文献   

19.
A pulsed ultrasonic method has been used to measure the speeds of longitudinal and transverse elastic waves along [100] and [110] in single crystals of NaxK1-xBr and NaxK1–xCl solid solutions in the range 20–180°C; the elastic constants cik have been determined. These values have been extrapolated to 0°K, while the bulk modulus and shear modulus have been calculated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 76–81, January, 1973.  相似文献   

20.
Mg2Sn电子结构及热力学性质的第一性原理计算   总被引:1,自引:0,他引:1       下载免费PDF全文
刘娜娜  宋仁伯  孙翰英  杜大伟 《物理学报》2008,57(11):7145-7150
采用基于第一性原理的赝势平面波方法系统地计算了Mg2Sn基态的电子结构、弹性常数和热力学性质.计算结果表明Mg2Sn的禁带宽度为0.1198eV.运用线性响应方法确定了声子色散关系和态密度,得出Mg2Sn的热力学性质如等容比热和德拜温度.计算Mg2Sn的热导率并与实验数据相比较. 关键词: 第一性原理 电子结构 弹性常数 热力学性质  相似文献   

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