Physical Review B
The van der Waals (vdW) interactions between carbon nanotubes (CNTs) were studied based on the continuum Lennard-Jones model. It was found that all the vdW potentials between two arbitrary CNTs fall on the same curve when plotted in terms of certain reduced parameters, the well depth, and the equilibrium vdW gap. Based on this observation, an approximate approach is developed to obtain the vdW potential between two CNTs without time-consuming computations. The vdW potential estimated by this approach is close to that obtained from complex integrations. Therefore, the developed approach can greatly simplify the calculation of vdW interactions between CNTs.
关键词:
molecules;clusters;bundles;growth;phase;c-60
Lin LI
,
O.Van Der Biest
,
Peiling WANG
材料科学技术（英）
The application of substitutional model in oxide systems, in comparison with that of sublattice model, is discussed. The results show that in the case of crystalline phases and liquid phases without molecular-like associates or the shortage of element in sublattice, these two models get consistent in the description of the formalism of Gibbs free energies of phases and obtain the same result of phase diagram calculation when the valence of the cations keep the same.
关键词:
Oxide systems
,
null
,
null
Chemical Physics Letters
The potential energies of van der Waals (VDW) interactions between two parallel, infinitely long and perfect SWNTs with identical, and different sizes were studied based on the continuum Lennard-Jones model. The conclusion of Girifalco's work on (n, n) SWNTs that the potentials of SWNT-SWNT fell on a single curve, is also applicable to SWNTs with different sizes. We further obtained the corresponding constants of the well depth \phi(0)\ and equilibrium VDW gap g(0) for SWNTs with a radius from 2 to 25 Angstrom. (C) 2005 Elsevier B.V. All rights reserved.
关键词:
carbon nanotubes;graphite;bundles;c-60;moduli;ropes
Journal of Physical Chemistry B
The potential energies of van der Waals interactions between two multiwalled carbon nanotubes (MWNTs) as well as two carbon nanoparticles (CNPs) were calculated and compared on the basis of the continuum Lennard-Jones model. The well depth of the potential is 1 order of magnitude higher for MWNTs than for CNPs, indicating that MWNTs and CNPs can be separated from each other through polymer-induced steric stabilization. On the basis of this prediction, a novel method for the purification of MWNTs was proposed. The method involves a high-temperature annealing ( 2600 degrees C, 1 h) followed by an extraction treatment with a selected dispersing agent. While the annealing process evaporates the metal particles, the extraction treatment removes CNPs. The quality of the nanotubes obtained after purification was examined by laser Raman, thermogravimetric analysis, and electron microscopy observations.
关键词:
decomposition;hydrocarbons;temperature;nanofibers;pyrolysis;monoxide;bundles;purity;gas
Y. Q. Jia1)
,
J. G. Li1)
,
Y. M. Wang2)
,
L. X. Ding2)
,
X. M . Qin1) and X. D. Sun1)1) School of Materials and Metallurgy
,
Northeastern University
,
Shenyang 110006
,
China2) Department of Materials
,
School of Mechanical Engineering
,
Shenyang University
,
Shenyang 110044
,
China
金属学报(英文版)
Using yttriu m nitrate as the m other salt , synthesis of ultrafine yttria po w der through w et che mical route w as investigated . Choice of precipitant has dra m atic effects on co m position ,particle size distribution and particle m orphology of the precipitates . When a m m onia solutionw as used as the precipitant , the precursor precipitate w as m ainly Y2( O H) 5 14( N O3) 0 86· H2 O with co m paratively large particle size , broad size distribution and co m plex particleshapes . When sodiu m hydroxide solution w as used , roughly spherical α Y( O H)3·3 H2 Opre cipitate w ith sm all particle size and narro w size distribution w as obtained . The transfor m a tion sequence of dry α Y( O H)3 ·3 H2 O gel during calcination w as determ ined to be α Y( O H) 3·3 H2 O→ Y O O H→ Y2 O3 . After calcining at 600 ℃ for 1 hour , both Y2( O H) 5 14( N O3) 0 86· H2 O and α Y( O H) 3·3 H2 O transfor m to well crystallized Y2 O3 pow ders ,w ith particle sizes of 50 ～3000 n m and 20 n m , respectively .
关键词:
KEYW ORDS yttria
,
null
,
null
,
null
张霞
,
苏希玉
,
侯芹英
,
侯艳丽
低温物理学报
doi:10.3969/j.issn.1000-3258.2008.03.011
考虑态密度的Van Hove奇异性和非电声作用,我们在BCS理论框架内研究了HgBa2Cun-1CunO2n+2+δ(n=1,2,3)系统的超导转变温度和同位素效应.结果表明,当同时考虑Van Hove奇异性和非电声作用时,可以更好地解释HgBa2Cun-1CunO2n+2+δ(n=1,2,3)系统的超导性质.
关键词:
Van Hove奇异性
,
非电声作用
,
超导转变温度
,
同位素效应
Acta Physica Sinica
High quality and large-size single crystals of CaTi(2) O(4) were prepared by the molten salt flux method. The X-ray diffraction and the EDS results showed that all the CaTi(2) O(4) crystals have the rom temperature lattice parameters a = 9. 781 angstrom, b = 9. 966 angstrom and c = 3. 148 angstrom, and all the samples have perfect stoichiometric composition. Through the magnetic susceptibility measurement, we first obtained the Van-Vleck paramagnetic parameter of CaTi(2) O(4) of 6. 85 x 10(-5) cm(3)/mol, and Cure-Weiss temperature of -0. 44 K, revealing that CaTi(2) O(4) is a weak ferromagnetic compound. Further more, the existence of Ti-Ti dimer was confirmed by anisotropy measurement, the structure and direction of the antiferromagnetic dimer chains were also determined.
关键词:
CaTi(2) O(4);magnetic susceptibility;anisotropy;antiferromagnetic;dimer;transition
Acta Physica Sinica
Large, high quality single crystals of Dy2Ti2O7 have been successfully grown by the floating zone technique in an infrared image furnace. The obtained single crystal has been characterized by X-ray diffraction at room temperature and is shown to have the face centred cubic structure, Fd (3) over barm, with a room temperature lattice parameter a = 1.0112(2) nm. The full-width at half-maximum of rocking curves of [111] and [400] Bragg peaks are 0.07 degrees and 0.05 degrees, respectively. Magnetic susceptibility measurements give a Van Vleck paramagnetic parameter of 2.46 x 10(-5) m(3)/mol, the effective moment mu(eff) = 10.24(4)mu(B) and Cure-Weiss temperature Theta(CW) = 1.1 K, indicating weak ferromagnetism for the Dy2Ti2O7 single crystal. The comparative studies of the experiment and theoretical analysis reveal that the long-ranged dipole-dipole interactions dominate the magnetic behaviors of this kind of spin ice system, and the dipolar energy scale D-nm = 3.00 K.
关键词:
Dy2Ti2O7;crystal growth with floating zone method;correlated electron;system;spin ice;earth titanate pyrochlores;spin ice;ferromagnet;liv2o4;oxide
Science in China Series B-Chemistry
The equation of the state of the hydrogen bonding fluid system of A(a)D(d) type is studied by the principle of statistical mechanics. The influences of hydrogen bonds on the equation of state of the system are obtained based on the change in volume due to hydrogen bonds. Moreover, the number density fluctuations of both molecules and hydrogen bonds as well as their spatial correlation property are investigated. Furthermore, an equation describing relation between the number density correlation function of "molecules-hydrogen bonds" and that of molecules and hydrogen bonds is derived. As application, taking the van der Waals hydrogen bonding fluid as an example, we considered the effect of hydrogen bonds on its relevant statistical properties.
关键词:
hydrogen bonding fluid;equation of state;fluctuation;correlation;effect;liquid methanol;temperature;water;dependence
