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1.
LIU Zhong-Li CHENG Yan TAN Ni-Na GOU Qing-Quan 《理论物理通讯》2006,46(3):573-576
The thermodynamic properties of LiBC are investigated by using the full-potential linearlzed muffin-tin orbital method (FP-LMTO) within the frame of density functional theory (DFT) and using the quasi-harmonic Debye model. The dependencies of the normalized lattice parameters a/a0 and c/c0, the ratio (c/a)/2, the normalized primitive volume V/V0 on pressure and temperature are successfully obtained. It is found that the interlayer covalent interactions (Li-B bonds or Li-C bonds) are more sensitive to temperature and pressure than intralayer ones (B-C bonds), as gives rise to the extreme lattice anisotropy in the bulk hop LiBC. 相似文献
2.
We employ a first-principles plane wave method with the
relativistic analytic pseudopotential of Hartwigsen, Goedecker and Hutter
(HGH) scheme in the frame of DFT to calculate
the equilibrium lattice parameters and the thermodynamic properties of
AlB2 compound with hcp structure. The obtained lattice parameters are in
good agreement with the available experimental data and those calculated by
others. Through the quasi-harmonic Debye model, obtained successfully are
the dependences of the
normalized lattice parameters a/a0 and c/c0 on pressure P, the normalized
primitive cell volume V/V0 on pressure P, the variation of the thermal
expansion α with pressure P and temperature T, as well as the Debye
temperature \ThetaD and the heat capacity CV on pressure P and
temperature T. 相似文献
3.
Arash Boochani Heidar Khosravi Jabbar Khodadadi Shahram Solaymani Masoud Majidiyan Sarmazdeh Rohollah Taghavi Mendi Sayed Mohammad Elahi 《理论物理通讯》2015,63(5):641-647
By FP-LAPW calculations, the structural, elastic, Debye and Curie temperatures, electronic and magnetic properties of Co2 VAl are investigated. The results indicate that Ferromagnetic(FM) phase is more stable than AntiFerromagnetic(AFM) and Non-magnetic(NM) ones. In addition, C11–C12 0, C44 0, and B 0 so Co2 VAl is an elastically stable material with high Debye temperature. Also, the B/G ratio exhibits a ductility behavior. The relatively high Curie temperature provides it as a favorable material for spintronic application. It's electronic and magnetic properties are studied by GGA+U approach leading to a 100% spin polarization at Fermi level. 相似文献
4.
WANG Yong-Liang CUI Hong-Ling YU Bai-Ru CHEN Xiang-Rong 《理论物理通讯》2008,49(2):489-492
The elastic properties of the wurtzite-type aluminum nitride (w-AlN) are investigated by ab initio plane-wave pseudopotential density functional theory method. The pressure dependences of the normalized primitive cell volume V/Vo, the elastic constants cij, the aggregate elastic modulus (B, G, E), the Poisson's ratio (v), and the Debye temperature θD are successfully obtained. From the elastic constants of the w-AlN under pressure, we find that the w-AlN should be unstable at higher pressure than 61.33 GPa. 相似文献
5.
The equations of state (EOS) and other thermodynamic properties of TiB2 are investigated using ab initio plane-wave pseudopotential density functional theory method. The obtained results are in good agreement with the experimental measured data and other theoretical calculated ones. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of relative volume V/V0 on pressure P, cell volume V on temperature T, and Debye temperature Θ and specific heat CV on pressure P are successfully obtained. 相似文献
6.
采用基于密度泛函理论的第一性原理平面波赝势方法研究ZrV2的晶体结构和弹性,利用准谐Debye模型计算在不同温度(T=0~1200 K)和不同压强(P=0~20 GPa)下ZrV2的热力学性质,包括弹性模量与压强,热熔与温度,以及热膨胀系数与温度和压力的关系.结果表明:计算的ZrV2晶格常数与实验值符合较好,晶体材料的弹性常数随着压力增加而增加;在一定温度下,相对体积、热熔随着压强的增加而减小,德拜温度、弹性模量随着压强的增加而增加,且高压下温度对ZrV2热膨胀系数的影响小于压强的影响. 相似文献
7.
S. Mollah Z.A. Khan D.K. Shukla M. Arshad Ravi Kumar A. Das 《Journal of Physics and Chemistry of Solids》2008,69(4):1023-1028
Polycrystalline bulk ferromagnetic insulating (FMI) Ln0.85Ca0.15MnO3 (Ln=Nd, Pr and Sm) samples are prepared by standard solid-state reaction route and characterized. Powder X-ray diffraction (XRD) data of the manganites show single-phase character. Existing theoretical models predict that the high temperature (T>θD/2, θD being the Debye temperature) dc conductivity (σdc) of these samples is due to adiabatic small polaron-hopping conduction. Greaves’ and Mott's variable range hopping (VRH) conduction mechanisms are not suitable to explain the σdc data at low temperature (T<θD/2). 相似文献
8.
We report magnetic susceptibility and specific heat measurements on polycrystalline samples of the 30 K superconductor Ba0·6K0·4BiO3. Normal-state magnetization measurements indicate a Pauli-paramagnetic susceptibility of χpauli = 2.3 × 10−5 emu/mole, from which we infer a value for the density of states at the Fermi level of N(0) = 8.6 × 10 21ev−1cm.−3 Specific heat measurements performed between 1.6 K and 40 K indicate that considerable lattice softening occurs at low temperatures; the effective Debye temperature drops from 280 K at 35 K to 210 K at 4 K, implying that soft phonon modes are present in this compound. This result indicates that conventional phonon-mediated interactions may be responsible for the high transition temperature exhibited by Ba0·6K0·4BiO3. 相似文献
9.
Andreev N.E. Kalmykov S.Y. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2000,28(4):1106-1115
Spectral features of a large-angle stimulated Raman scattering (LA SRS) of a short electromagnetic pulse in an underdense plasma, which are caused by the presence in a plasma of a given linear long-wavelength electron plasma wave (LW EPW), are investigated. It is shown that the LW EPW, whose phase velocity coincides with a group velocity of a pulse and a density perturbation normalized to a background electron density δnLW/n0 exceeds the ratio of the electron plasma frequency to the laser frequency ωpe/ω0 suppresses the well-known Stokes branch of the weakly coupled LA SRS. Under the same condition, the anti-Stokes band appears in the spectrum of the scattered radiation. Variation of a scattering angle and an electron temperature do not significantly modify qualitative features of the effect. In the case of strongly coupled LA SRS, the maximum of the increment is decreased by nearly one-half for δnLW/n0~(a0ωpe /ω0)2/3≫ωpe /ω0, where a0 is an amplitude of an electron quiver velocity in the laser field normalized to a speed of light c, and it decreases further with an increase in plasma density perturbation in LW EPW 相似文献
10.
The thermodynamic properties of LiBC are investigated by using the full-potential linearized muffin-tin orbital method (FP-LMTO) within the frame of density functional theory (DFT) and using the quasi-harmonic Debye model. The dependencies of the normalized lattice parameters a/a0 and c/c0, the ratio (c/a)/2, the normalized primitive volume V/V0 on pressure and temperature are successfully obtained. It is found that the interlayer covalent interactions (Li-B bonds or Li-C bonds) are more sensitive to temperature and pressure than intralayer ones (B-C bonds), as gives rise to the extreme lattice anisotropy in the bulk hcp LiBC. 相似文献
11.
研究了磁场作用下石墨烯中电子与表面光学声子弱耦合情况下的极化子的性质。采用线性组合算符和Pekar变分法分别推导出了石墨烯中弱耦合极化子的基态能量E0、第一激发态能量E1和跃迁频率ω随磁场强度B和德拜截止波数kd之间的变化关系。数值计算结果表明,极化子的基态能量E0随磁场强度B变化的曲线(kd一定时)和E0随kd的变化曲线(B一定时)均会分裂成对称的两条,并且当B一定时E0的绝对值随kd的增加而增加。在kd一定时,极化子的第一激发态能量E1和跃迁频率ω均为磁场B的增函数;在B一定时,E1和ω均随kd的增加而增大。 相似文献
12.
13.
Elastic and thermodynamic properties of c-BN from first-principles calculations 总被引:1,自引:0,他引:1
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The elastic constants and thermodynamic properties of c-BN are
calculated using the first-principles plane wave method with the
relativistic analytic pseudopotential of the Hartwigen, Goedecker
and Hutter (HGH) type in the frame of local density approximation
and using the quasi-harmonic Debye model, separately. Moreover, the
dependences of the normalized volume V/V0 on pressure P, as
well as the bulk modulus B, the thermal expansion α, and the
heat capacity CV on pressure P and temperature T are also
successfully obtained. 相似文献
14.
The elastic constants of superconducting MgB2 are
calculated using a molecular dynamics method (MD) with shell model. The
lattice parameters, five independent elastic constants, equations of state
(EOS), Debye temperature, and bulk modulus of MgB2 are obtained.
Meanwhile, the dependence of the bulk modulus B, the lattice parameters a and c, and the unit cell volume V on the applied pressure are presented. It is
demonstrated that the method introduced here can well reproduce the
experimental results with a reasonable accuracy. 相似文献
15.
The temperature dependence of the upper critical fields, both perpendicular Hc2 and parallel Hc2 to layer planes of ferromagnet/superconductor bi- and multilayers, is theoretically investigated. The secular equation of the superconducting order parameter for determining the phase diagram (H, T) is obtained by solving exactly the linearized Usadel equations in the multimode method taking into account the material parameter values. For the bilayers system, the influence of the boundary resistivity on the critical fields, and the dimensional crossover behavior of Hc2(T) are studied in details. For the multilayered structure, the effects of the π-phase state on both the superconducting transition temperature Tc and the upper critical fields (Hc2, and Hc2) are also considered. The nonmonotonic Tc behaviors are predicted. The interplay between 0- and π-phases leading to the strong oscillations of Tc as well as the temperature dependence of the zero temperature critical fields on the ferromagnetic layer thickness are investigated theoretically. 相似文献
16.
T. D. Ford T. G. Call M. A. Stark M. L. Origlia K. Ballerat-Busserolles E. M. Woolley 《Journal of Molecular Liquids》2001,90(1-3):139-148
We have used a vibrating-tube densimeter to investigate the densities and volumetric properties of aqueous solutions, and a fixed-cell scanning calorimeter to measure aqueous solution heat capacities. Solutions investigated include sugars, neutral weak acids and bases, neutralized acids and bases, neutral and protonated amino acids, surfactants, and both strong and ion-paired electrolytes. We have made measurements at molalities m from 0.005 mol·kg−1 to 0.5 mol·kg−1, at temperatures T from 278.15 K to 393.15 K, and at the pressure P = 0.35 MPa. We have calculated the apparent molar volumes Vφ and apparent molar heat capacities Cp,φ of the solutions and fit them by regression to equations that describe the surfaces (Vφ, T, m) and (Cp,φ, T, m). These results reflect changes and differences in both solute-solute and solute-solvent interactions. Standard state partial molar volumes V2° and heat capacities Cp,2° were estimated by extrapolation to the M = 0 mol·kg−1 plane of the fitted surfaces. We have calculated (Δr,Cp,m, T, m) surfaces for various proton dissociation reactions, and we have created surfaces representing (ΔrHm, T, m) and (pQa, T, m) by integration of our (ΔrCp,m, T, m) surfaces using values for (ΔrHm, m) and (pKa, m) at a reference T as integration constants. We have also created surfaces representing (ΔrSm, T, m) and (ΔrVm, T, m) for these dissociation reactions. 相似文献
17.
Epitaxial thin films of the conductive ferromagnetic oxide SrRuO3 were grown on an (0 0 1) SrTiO3 (STO) substrate by using DC sputtering technique. The magnetic and magnetoresistive properties of the films were measured by applying the magnetic field both perpendicular (out-of-plane) and parallel (in-plane) to the film plane and ever maintaining the direction of the applied field perpendicular to that of the transport current. The films grown on an (0 0 1) STO substrate showed identical magnetization properties in two orthogonal crystallographic directions of the substrate, [1 0 0]S and [0 0 1]S (in-plane and out-of-plane geometry), which suggests the presence of a multi domain structure within the plane of the film. For such samples, no anisotropic field (hard axis) along de [0 0 1]s direction, i.e., perpendicular to the film-plane could be detected. Nevertheless, a distinguishable temperature dependent out-of-plane anisotropic magnetoresistance (MR) along with strong temperature dependent low field hysteretic MR(H) behavior was detected for the studied films. A negative MR ratio MR(T)=[ρ(μ0H=9 T; T)−ρ( μ0H=0 T; T)]/ρ( μ0H=0 T; T) on the order of a few percent, with maximums of 6% and 4% (right at the Curie temperature, TC 160 K) was calculated for an in-plane and out-of plane measuring geometry, respectively. In addition there is an equally strong MR effect at low temperatures, which might be related to the temperature dependence of the magnetocrystalline anisotropy together with a magnetization rotation. Both the MR(T) behavior and the achieved values (except for T<30 K) are similar to those obtained on SrRuO3 films grown on 2° miscut (0 0 1) STO substrates with the current parallel to the field and parallel to the direction, which was identified as the easier axis for magnetization. 相似文献
18.
We have investigated the structural and elastic properties
of MgB2 under high pressures using the full-potential linearized
muffin-tin orbital (FP-LMTO) scheme within the generalized gradient
approximation correction (GGA) in the frame of density functional
theory. The calculated pressure dependence of the normalized
volume is in excellent agreement with the experimental results.
At the same time the elastic constants and acoustic anisotropy
as a function of applied pressure are presented. Through the
quasi-harmonic Debye model, we also investigate the thermodynamic
properties of MgB2. 相似文献
19.
V.K. Sinha S.K. Malik D.T. Adroja J. Elbicki S.G. Sankar W.E. Wallace 《Journal of magnetism and magnetic materials》1989,80(2-3):281-284
The DyTiFe11 - xCox (x = 0, 1, 3), HoTiFe11 - xCox (x = 0, 3) and ErTiFe11 compounds, all exhibiting the T hMn12-type structure, were studied for their ac susceptibility in the temperature range 20–300 K. The Dy- and Ho-containing compounds exhibited spin reorientation from axial to cone to planar, or from axial to cone in the temperature range 250-50 K, as expected. In this structure Dy and Ho with negative second-order Stevens' coefficients (J < 0) favor planar rare earth sublattice anisotropy, while Fe and Co sublattices favor uniaxial and planar anisotropies, respectively and would be in competition as a function of temperature. A spin-reorientation type of behavior was also observed in the ErTiFe11 compound near 50 K. This observation appears to imply that, in this compound, the higher-order crystal-field terms are important. The magnetization data revealed that in these systems the rare earth and transition metal sublattices coupled antiparallel, as is normally the case in the heavy rare-earth-transition-metal compounds. 相似文献
20.
Structural and thermodynamic properties of wurtzite-type aluminium nitride from first-principles calculations
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The lattice parameter, bulk modulus and its pressure derivative of
the wurtzite-type aluminium nitride (w-AlN) are investigated by using
the Cambridge Serial Total Energy Package (CASTEP) program in the
framework of Density Functional Theory (DFT). The calculated results
are in good agreement
with the available experimental data and other theoretical results.
Through the quasi-harmonic Debye model, the dependences of the
normalized lattice parameters $a/a_{0}$ and $ c/c_{0}$, axial ratio
$c/a$, normalized primitive-cell volume $V/V_{0}$, Debye
temperature ${\it\Theta} _{\rm D} $ and heat capacity $C_{\rm V}$ on
pressure $P $ and temperature $ T$ are obtained. It is found that the
interlayer covalent interactions (Al-N bonds) are more (even a
little) sensitive to temperature and pressure than intralayer ones
(N--N bonds), which gives rise to a little lattice anisotropy in the
w-AlN. 相似文献