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1.
M. N. Magomedov 《Physics of the Solid State》2010,52(6):1283-1292
The dependences of the specific surface energy, the surface tension, and the surface pressure on the size, the surface shape,
and the temperature of a nanodiamond with a free surface have been investigated using the Mie-Lennard-Jones interatomic interaction
potential. The nanocrystal has the form of a parallelepiped faceted by the (100) planes with a square base. The number of
atoms N in the nanocrystal varies from 5 to ∞. The isothermal isomorphic dependences of the specific surface energy, its isochoric
derivative with respect to the temperature, the surface tension, and the surface pressure on the nanodiamond size have been
calculated at temperatures ranging from 20 to 4300 K. According to the results of the calculations, the surface energy under
this conditions is positive, which indicates that the nanodiamond cannot be fragmented at temperatures up to 4300 K. The surface
pressure for the nanodiamond P
sf
(N) ∼ N
−1/3 is considerably less than the Laplace pressure P
ls
(N)−1/3 ∼ N
−1/3 for the same nanocrystal at the given values of the temperature, the density, and the number of atoms N. As the temperature increases from 20 to 4300 K, the lowering of the isotherm P
sf
(N) is considerably more pronounced than that of the isotherm P
ls
(N). At high temperatures, the isotherm P
sf
(N) changes the shape of the size dependence and goes to the range of extension of small nanocrystals. It has been demonstrated
that the lattice parameter of the nanodiamond can either decrease or increase with a decrease in the nanocrystal size. The
most significant change in the lattice parameter of the nanodiamond is observed at temperatures below 1000 K. 相似文献
2.
V. A. Konstantinov V. P. Revyakin V. V. Sagan O. I. Pursky V. M. Sysoev 《Journal of Experimental and Theoretical Physics》2011,112(2):220-225
Thermal conductivity Λ
P
of solid cyclohexane is measured at a pressure P = 0.1 MPa in the temperature range from 80 K to the melting point, which covers the ranges of low-temperature orientationally
ordered phase II and high-temperature orientationally disordered phase I. Thermal conductivity Λ
V
is measured at a constant volume in orientationally disordered phase I. The thermal conductivity measured at atmospheric
pressure decreases with increasing temperature as Λ
P
∝ T
−1.15 in phase II, whereas Λ
P
∝ T
−0.3 in phase I. As temperature increases, isochoric thermal conductivity Λ
V
in phase I increases gradually. The experimental data are described in terms of a modified Debye model of thermal conductivity
with allowance for heat transfer by both phonons and “diffuse” modes. 相似文献
3.
Diffusion and solubility of helium in Ce0.8Gd0.2O1.9 − δ ceramics (δ = 0, 0.015) with a submicrocrystal structure are studied by thermodesorption of helium from preliminarily saturated
(in the gas phase) crystals at temperatures of 613 and 673 K in the saturated pressure range 0–21 MPa. It is shown that, in
this ceramics (δ = 0), the defect-trap diffusion mechanism operates. The main positions for dissolution are neutral anion
vacancies formed as a result of thermal dissociation of impurity-vacancy complexes and saturated up to ∼1 × 1019 cm−3 at P = 6 MPa and T = 673 K. The dissociation energy of the complex and the energy of helium dissolution in the neutral anion vacancy are estimated
at ∼2 eV and below −0.3 eV, respectively. 相似文献
4.
A. U. Sheleg V. G. Hurtavy S. N. Mustafaeva E. M. Kerimova 《Physics of the Solid State》2011,53(3):472-475
The temperature dependences of the electrical conductivity and the permittivity of TlInSe2 and TlGaTe2 crystals unirradiated and irradiated with 4-MeV electrons at a doze of 1016 cm−2 have been investigated. It has been established that electron irradiation leads to a decrease in the electrical conductivity
σ and the permittivity ɛ over the entire temperature range under study (90–320 K). It has been revealed that the TlInSe2 and TlGaTe2 single crystals undergo a sequence of phase transitions characteristic of crystals of this type, which manifest themselves
as anomalies in the temperature dependences σ = f(T) and ɛ = f(T). Electron irradiation at a doze of 1016 cm−2 does not affect the phase transition temperatures of the crystals under investigation. 相似文献
5.
Wanwimon Banlue Naratip Vittayakorn 《Applied Physics A: Materials Science & Processing》2008,93(2):565-569
The solid solution between the antiferroelectric PbZrO3 (PZ) and relaxor ferroelectric Pb(Co1/3Nb2/3)O3 (PCoN) was synthesized by the columbite method. The phase structure and thermal properties of (1−x)PZ–xPCoN, where x=0.0–0.3, were investigated. With these data, the ferroelectric phase diagram between PZ and PCoN has been established. The
crystal structure data obtained from XRD indicates that the solid solution PZ–PCoN, where x=0.0–0.3, successively transforms from orthorhombic to rhombohedral symmetry with an increase in PCoN concentration. The AFE→FE
phase transition was found in the compositions of 0.0≤x≤0.10. The AFE→FE phase transition shift to lower temperatures with higher compositions of x. The width of the temperature range of FE phase was increased with increasing amount of PCoN. It is apparent that the replacement
of the Zr4+ ion by (Co1/3Nb2/3)4+ ions would decrease the driving force for antiparallel shift of Pb2+ ions, because they interrupt the translational symmetry. This interruption caused the appearance of a rhombohedral ferroelectric
phase when the amount of PCoN was more than 10 mol%. 相似文献
6.
Intergalactic magnetic fields are assumed to have been spontaneously generated at the reheating stage of the early Universe,
due to vacuum polarization of non-Abelian gauge fields at high temperature. The fact that the screening mass of this type
of fields has zero value was discovered recently. A procedure to estimate their field strengths, B(T), at different temperatures is here developed, and the value B(T
ew)∼1014 G at the electroweak phase transition temperature is derived by taking into consideration the present value of the intergalactic
magnetic field strength, B
0∼10−15 G, coherent on the ∼1 Mpc scale. As a particular case, the standard model is considered and the field scale at high temperature
is estimated in this case. Model-dependent properties of the phenomena under investigation are briefly discussed, too. 相似文献
7.
S. S. Murzin 《JETP Letters》2010,91(3):155-157
It has been shown that the observation of the transitions between the dielectric phase and the integer-quantum-Hall-effect
phases with the quantized Hall conductivity σ
xy
q ≥ 3e
2/h announced in a number of works is unjustified. In these works, the crossing points of the magnetic-field dependence of the
diagonal resistivity ρ
xx
at different temperatures T and ωcτ = 1 have been misidentified as the critical points of the phase transitions. In fact, these crossing points are due to the
sign change of the derivative dρ
xx
/dT owing to the quantum corrections to the conductivity. Here, ωc = eB/m is the cyclotron frequency, τ is the transport relaxation time, and m is the effective electron mass. 相似文献
8.
Yu. P. Petrov Yu. K. Karasevich S. V. Turetskii 《Russian Journal of Physical Chemistry B, Focus on Physics》2010,4(4):566-573
The kinetics of nitromethane (NM) decomposition and the observed rate constant of the process were measured behind reflected
shock wave using absorption spectroscopy at λ = 230 nm, temperatures of 1060 to 1350 K, pressure of ∼40 atm, and initial reactant
concentration within 30–100 ppm. It was observed that, at the initial stage, nitromethane decomposes exponentially, without
autoacceleration. The results of numerical simulations with the help of three most known kinetic schemes of nitromethane decomposition
proved to be in close to agreement with our experimental data over the entire temperature range covered. It was demonstrated
that the measured rate constant is identical to the rate constant of the dissociation CH3NO2 → CH3 + NO2. The temperature dependence of k
1 was approximated by the Arrhenius formula k
1 = 2.57 × 1014 exp(−52.85/RT) s−1 (activation energy in kcal/mol), which suggests that the nitromethane dissociation proceeds in the falloff pressure region. 相似文献
9.
Infrared absorption and Raman study ofβ-Ni(OH)2 has been carried out up to 25 GPa and 33 GPa, respectively. The frequency ofA
2u
internal antisymmetric stretching O-H mode decreases linearly with pressure at a rate of −0.7 cm−1/GPa. The FWHM of this mode increases continuously with pressure and reaches a value of ∼ 120 cm−1 around 25 GPa. There was no discernible change observed in the frequency and width of the symmetric stretchingA
1g
O-H Raman mode up to 33 GPa. The constancy of the Raman mode is taken as a signature of the repulsion produced by H-H contacts
in this material under pressure. Lack of any discontinuity in these modes suggests that there is no phase transition in this
material in the measured pressure range. 相似文献
10.
本文采用第一性原理框架下的赝势平面波方法结合振动类德拜模型研究了α,β和γ-Si3N4在高温下的点阵常数,弹性常数和弹性模量.研究发现三种同质异相体的体模量都很高.β-Si3N4在低温下表现出脆性,在高温下则表现出延展性.γ-Si3N4在低温和高温下都是脆性的共价化合物.β → γ 相变的相界斜率为正值,说明在较高温度时合成γ-Si3N4所需的压强也较高.α → γ 相变的相界可以表示成 P=16.29- 1.835-10-2 T+9.33945-10-5T2-2.16759-10-7T3+2.91795-10-10T4.本文还分析了Si3N4同质异相体在高压下的态密度和能带.在α-Si3N4中主要是Si-s, p和N-s,p的轨道杂化对晶体的稳定性起作用.α和β-Si3N4都具有ΓV-ΓC类型的间接带隙(分别是4.9~eV和4.4~eV)而γ-Si3N4具有直接带隙(3.9~eV). 研究还发现α-Si3N4和β-Si3N4的价带顶分别沿着Γ-M和Γ-A方向.本文的计算结果和已有的实验数据是一致的. 相似文献
11.
We revisit the problem of a two-dimensional polymer ring subject to an inflating pressure differential. The ring is modeled
as a freely jointed closed chain of N monomers. Using a Flory argument, mean-field calculation and Monte Carlo simulations, we show that at a critical pressure,
pc ∼ N-1, the ring undergoes a second-order phase transition from a crumpled, random-walk state, where its mean area scales as 〈A〉 ∼ N, to a smooth state with 〈A〉 ∼ N2. The transition belongs to the mean-field universality class. At the critical point a new state of polymer statistics is
found, in which 〈A〉 ∼ N3/2. For p ≫ pc we use a transfer-matrix calculation to derive exact expressions for the properties of the smooth state. 相似文献
12.
The temperature variation of the lattice parameter of CsPbCl3 in the cubic phase has been studied by x-ray method, from a determination of the precision lattice parameter at various temperatures,
ranging from 50°C to 400°C. The coefficient of thermal expansion of CsPbCl3 can be expressed by the quadratic equation,α
T
= 21.6 × 10−6 + 2.44 × 10−9
T + 5.90 × 10−11
T
2. 相似文献
13.
V. V. Brazhkin A. G. Lyapin R. N. Voloshin S. V. Popova Yu. A. Klyuev A. M. Naletov S. C. Bayliss A. V. Sapelkin 《JETP Letters》1999,69(11):869-875
The results of an investigation of the transformation of C60 fullerite to diamond under pressure through intermediate three-dimensionally polymerized and amorphous phases are reported.
It is found that treatment of fullerite C60 at pressures 12–14 GPa and temperatures ∼1400°C produces a nanocrystalline graphite-diamond composite with a concentration
of the diamond component exceeding 50%. At lower temperatures (700–1200°C) nanocomposites consisting of diamondlike (sp
3) and graphitic (sp
2) amorphous phases are formed. The nanocomposites obtained have extremely high mechanical characteristics: hardness comparable
to that of best diamond single crystals and fracture resistance two times greater than that of diamond. Mechanisms leading
to the transformation of C60 fullerite into diamond-based nanocomposites and the reasons for the high mechanical characteristics of these nanocomposites
are discussed.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 11, 822–827 (10 June 1999) 相似文献
14.
Explicit expressions have been derived for the volume dependence of electron-phonon coupling strength (λ) and the Coulomb pseudopotential (μ*) considering the variation of Fermi momentum (κ
F) and Debye temperature (θ
D) with volume. Ashcroft’s model pseudopotential and RPA form of dielectric screening have been used for obtaining pressure
dependence of transition temperature (T
C) and the logarithmic volume derivative (Φ) of the effective interaction strength (N
0
V) for metallic glass superconductor Mg70Zn30. It has been observed that T
C of the metallic glass Mg70Zn30 decreases rapidly with increase of pressure and the superconducting phase disappears at about 30% decrease of volume, for
which the μ* curve shows a minimum and an elbow is formed in the Φ graph. 相似文献
15.
E. S. Itskevich 《Journal of Experimental and Theoretical Physics》1998,86(4):805-810
A study is made of the properties of the homologous series of mercury HTSC-cuprates HgBa2Can−1CunO2n
+2+δ with n=1–8. Experiments are conducted under pressure for samples with n=1–5. The Hg-1223 and Hg-1234 phases were synthesized using a controlled high pressure chamber. The oxygen content of an initial
mixture corresponding to the Hg-1234 phase was varied by changing the composition of the initial BaO/BaO2 oxides. The dependence of the superconducting transition temperature T
c
on the lattice constant a (and, therefore, on the oxygen content) and of T
c
max
and dT
c
max
/dp on n are convex upward up to n=4, 5. The maximum values always correspond to the Hg-1223 phase. Experimental T
c
max
(n) curves for the phases with n=1–6 and dT
c
max
/dp curves for n=1–5 are compared with Anderson’s theory (the so-called RVB model). A general analysis of these results indicates that the
mercury cuprates have an ideal structure for HTSC. The Hg-1223 phase is the “champion” in this ideal structure and the critical
temperature corresponding to this phase (T
c
=135 K) is the highest at atmospheric pressure.
Zh. éksp. Teor. Fiz. 113, 1474–1483 (April 1998) 相似文献
16.
M.H. Thoma S. Leupold U. Mosel 《The European Physical Journal A - Hadrons and Nuclei》2000,7(2):219-223
Assuming that ρ-mesons exist in a quark-gluon plasma at temperatures close to the QCD phase transition, we calculate the
dilepton production rate from q-ˉq annihilation via a ρ-meson state using Vector Meson Dominance. The result is compared to the rates from direct q-ˉq annihilation and from π+-π− annihilation. Furthermore we discuss the suppression of low mass dileptons if the quarks assume an effective mass in the
quark-gluon plasma.
Received: 8 September 1999 / Revised version: 22 October 1999 相似文献
17.
Cai Lingcang Chen Qifeng Gu Yunjun Zhang Ying Zhou Xianming Jing Fuqian 《中国科学G辑(英文版)》2005,48(2):695-705
Hugoniot curves and shock temperatures of gas helium with initial temperature 293 K and three initial pressures 0.6, 1.2,
and 5.0 MPa were measured up to 15000 K using a two-stage light-gas gun and transient radiation pyrometer. It was found that
the calculated Hugoniot EOS of gas helium at the same initial pressure using Saha equation with Debye-Hückel correction was
in good agreement with the experimental data. The curve of the calculated shock wave velocity with the particle velocity of
gas helium which is shocked from the initial pressure 5 MPa and temperature 293 K, i.e., theD ≈u relation,D=C
0+λu (u<10 km/s, λ=1.32) in a low pressure region, is approximately parallel with the fittedD ≈u (λ=1.36) of liquid helium from the experimental data of Nellis et al. Our calculations show that the Hugoniot parameter λ
is independent of the initial density p{in0}. TheD≈u curves of gas helium will transfer to another one and approach a limiting value of compression when their temperature elevates
to about 18000 K and the ionization degree of the shocked gas helium reaches 10−3. 相似文献
18.
This investigation is a contribution to the research on alternative cathode materials with much more promising performances
for lithium batteries. It deals with the electrochemical properties of iron phosphate compound FePO4, chemically prepared through the so-called sol–gel Pechini process, terminated by a calcination of the product precursor
at temperatures (T
c) ranging between 350°C and 650°C. A crystalline phase was obtained for temperatures ≥400°C. The particle size decreased with
the decrease in T
c, giving rise to a Brunauer–Emmett–Teller (BET)-specific surface area, S
BET, as high as 28 m2 g−1 for the sample annealed at 400°C. The electrochemical properties of FePO4-based composite cathodes were characterized on three-electrode laboratory cells. Charge–discharge cycling determined a maximum
reversible capacity of 132 mAh g−1, which fell with the increase in T
c. A direct correlation was established between the activity of the material and its active surface area. 相似文献
19.
The organic compound 1-chlorooctane exists in liquid state at ambient temperatures and has numerous synthetic applications.
Fourier transform infrared and Raman spectra of this molecule have been recorded in the range of 4000−400 cm−1 and 3500−200 cm−1, respectively. A detailed vibrational analysis in terms of assignment of the observed frequencies of this molecule for its
four most probable conformations in liquid phase, having symmetries C
s
and C
l
, has been done using normal co-ordinate calculations. The force-field transferred from already studied lower chain chloro-alkanes
is subjected to refinement so as to fit the observed infrared and Raman frequencies with those of calculated ones. The potential
energy distribution has also been calculated for each mode of vibration of the molecule for the most probable conformations
present in its liquid phase. 相似文献
20.
Calculations of the complex elastic moduli Ĉ(T) in dilute Cr alloys are compared to measurements of the velocity and damping of sound near T
N and at high temperatures T>T
N (T
N — Néel temperature). The thermodynamic calculation is based on the covalent bond model of 3d ions in a state with different numbers n of covalent electrons. The parameters A
ij
(n)
of indirect exchange between the ions of the i and j sublattices are expressed in terms of the covalent bond energy Γ
ij
(n)
. The stability of the charge and spin density waves (CDWs and SDWs) is found by a variational method and is determined by
the dispersion of Γ
ij
(n)
and by the Coulomb parameters U
n. For a small structural vector Q the phase diagram contains a superantiferromagnetic phase (SAFM) at temperatures T
N<T≲2T
N. The peak of the defect |ΔE(T)| of the modulus and of the sound damping Δh(T
N) near the first-order SDW-SAFM transition is determined by the structure of the transitional domain. Measurements of the
anomalous growth of E(T) at temperatures T>T
N make it possible to determine the magnetostriction constants λ(T) of Ce alloys in the SAFM phase on the basis of the SAFM theory.
Fiz. Tverd. Tela (St. Petersburg) 41, 1467–1472 (August 1999) 相似文献