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1.
M. K. Aliev G. R. Alimov T. M. Muminov B. A. Olimov Kh. I. Turkmenov I. Kholbaev L. I. Leonyuk R. F. Rumi 《Physics of the Solid State》1999,41(1):11-14
Y1Ba2Cu3O7−x
single crystals are investigated near T
c
≈92 K in fields 0<H⩽9 kOe using a modified ESR spectrometer. The temperature modulation method is used for the first time, together with the
traditional magnetic modulation method, to detect microwave responses in single crystals. Superconducting-transition peaks
shifted relative to one another in temperature and differing in shape are observed in the temperature dependence of the corresponding
signals ∂R/∂H and ∂R/∂T (R — microwave absorption). The evolution of these peaks as a function of the field and the angle π between H and the c axis of the single crystal is traced. It is shown that the difference in the temperature dependences of the derivatives ∂R/∂H and ∂R/∂T is due to the broadening of the superconducting transition characteristic of HTSCs.
Fiz. Tverd. Tela (St. Petersburg) 41, 14–17 (January 1999) 相似文献
2.
The effect of mechanical contacts between γ-Fe2O3 particles on the temperature of the γ-α structural transition in them is established by magnetic studies and differential
thermal analysis (DTA). The sample in which γ-Fe2O3 particles had no mechanical contacts with one another remained in the ferromagnetic state up to T
C = 630°C and had two exothermal DTA peaks. The first peak almost coincided with the Curie temperature, while the second peak
attributed to the γ → α structural transition corresponded to 760°C. The magnetic transition for particles with a larger number
of contacts was shadowed by the γ → α structural transition with a temperature lowered to 550°C. 相似文献
3.
B. A. Strukov E. P. Ragula S. Yu. Stefanovich I. V. Shnaidshtein S. V. Arkhangel’skaya A. Onodera 《Physics of the Solid State》1998,40(7):1193-1195
The specific heat of the ceramic and the permittivity of a single-crystal sample of LaBSiO5, a new ferroelectric in the stilwellite family, were measured in a temperature range which includes the phase transition
point (T
C=140 °C). The excess entropy of the phase transition ΔS=1.05 J/mol · K and the Curie-Weiss constant C
C-W=3.2×103 K were determined. The results indicate that the phase transition in this crystal is of a “mixed” nature and exhibits features
of a displacement-type transition and an order-disorder transition.
Fiz. Tverd. Tela (St. Petersburg) 40, 1310–1312 (July 1998) 相似文献
4.
A. I. Yakimov N. P. Stepina A. V. Dvurechenskii L. A. Shcherbakova 《Journal of Experimental and Theoretical Physics》1997,85(3):501-506
The temperature dependence of the hopping conductivity and the relaxation kinetics of the transient current in porous amorphous
silicon are investigated after treatment in a hydrogen plasma at 200 °C. It is discovered that posthydrogenation of the material
increases the dimension of the conducting channel from 2.5 to 3, while suppressing and slowing the relaxation of the transient
current. The results obtained are attributed to passivation of the electrically active dangling bonds on the pore surface
by hydrogen. It is concluded that electron transport in porous amorphous silicon in the temperature range T>T*, where T* lies in the range 130–270 K and depends on the density of states, takes place between superlocalized states of the internal
surface, which is enriched with dangling bonds and acts as a fractal percolation system. When the temperature is lowered below
T*, a transition to one-dimensional hopping conduction in the bulk silicon regions occurs.
Zh. éksp. Teor. Fiz. 112, 926–935 (September 1997) 相似文献
5.
The temperature-induced frequency shifts (1/ω)(∂ω/∂T)
p
are calculated from the pressure induced frequency shifts (1/ω)(∂ω/∂P)
T
using the observed frequencies at various pressures for the Raman modes of II and III in phase II (P > P
C
) of s-triazine. The values of the mode Grüneisen parameters γ
T
(isobaric) and γ
T
(isothermal) of those Raman modes studied here, are determined through the Pippard relations in the spectroscopically modified
forms for this crystal. The temperature-induced and the pressure-induced frequency shifts are then used to predict the pressure
dependence of the isothermal compressibility, thermal expansion and the specific heat in phase II (P > P
C
) of s-triazine. 相似文献
6.
The distinctive features of the low-frequency internal friction Q
−1(T) of (Cu-Sn)-Nb composites at high temperatures (up to 400°C) are investigated for strains in the range 10−5–10−4. Considerable hysteresis of Q
−1(T) in the heating-cooling cycle is recorded, including the presence of a minimum at ∼175°C when the sample is heated to 400°C
and two peaks P
2 (at 280°C) and P
1 (at ∼100°C) when the sample is cooled from 400°C. The activation energy of the anomalous internal friction background (up
to 175°C), the oxygen diffusion parameters, and the oxygen concentration in the niobium fibers (all of which govern the peak
P
2) are calculated, and the value and temperature dependence of the yield point of the bronze matrix (which govern the peak
P
1) are estimated.
Zh. Tekh. Fiz. 68, 114–117 (November 1998) 相似文献
7.
H.Y. Wang Z.W. Ma E.Y. Jiang Y.J. He H.S. Huang 《Applied Physics A: Materials Science & Processing》1999,68(5):559-562
The structure and magnetic properties of Fe-N and Fe-Ti-N films have been studied as a function of annealing temperature Ta with a transmission electron microscope and a vibrating sample magnetometer. The as-prepared Fe-N films consist of the γ′-Fe4N and α′′-Fe16N2 phases, and the Fe-Ti-N films are composed of the γ′-Fe4N, α′′-Fe16N2, and TiN phases. The structural changes with annealing temperature in the Fe-N films are distinct. The α′′-Fe16N2 decomposes into α+γ′ phases in the Fe-N film annealed at about 300 °C, and it disappears in the film annealed at 350 °C. Annealing of the Fe-Ti-N
films shows no structural changes between room temperature (RT) and 500 °C. The saturation magnetization 4πMS and coercivity Hc of the Fe-N films change drastically with the annealing temperature Ta, whereas those of the Fe-Ti-N films do not change with Ta up to 500 °C. These results indicate that the additon of Ti may improve the thermal stability of Fe-N films.
Recieved: 6 Juli 1998 / Accepted: 19 Oktober 1998 / Published online: 10 March 1999 相似文献
8.
Time differential perturbed angular correlation measurements of the 133–482 keVγ-γ cascade of181Ta in Hf-doped YBa2Cu3O7−x
are presented. The181Hf precurser nuclei are incorporated into the sample by thermal neutron irradiation. Two quadrupole interaction frequencies
are observed in the as-irradiated sample:v
Q1=161±10 MHz with intensityf
1=75%, asymmetry parameterη
1=0.32 and damping parameter Λ1=0.42, andv
Q2=1108±40 MHz withf
2=25%,η
2=0.62, and Λ2=0.60. On annealing the sample in air at various temperaturesT
a and quenching to room temperature,f
1 remained nearly constant forT
a<600°C andv
Q1 for all annealing temperatures indicating that these are insensitive to oxygen stoichiometry. This frequency is interpreted
to be due to181Hf substitutingY sites. BeyondT
a=600°C,f
1 increased and reached a constant value of 90% forT
a=800°C. The value ofv
Q2 showed a slight variation between 1086 and 1160 MHz, whilef
2 remained nearly constant at 25% forT
a<600°C. This component is identified to be due to181Hf substituting Cu 1 sites in the Cu-O chains of YBCO. Above 600°Cv
Q2 decreased and reached a value of 808 MHz beyond 750°C. 相似文献
9.
The absorption spectra and the melting and crystallization kinetics of CuCl nanocrystals in glass are investigated in the
range of particle radii 1–30 nm. Three discontinuities are found on the curves representing the size dependence of the melting
point T
m(R) and the crystallization point T
c(R). As the particle radius gradually decreases from 30 nm in the range R⩽12.4 nm there is a sudden 60° drop in the temperature T
c in connection with the radius of the critical CuCl nucleus in the melt. A 30° drop in T
m is observed at R=2.1 nm, and a second drop of 16° in the temperature T
c is observed for CuCl particles of radius 1.8 nm. The last two drops are associated with changes in the equilibrium shape
of the nanoparticles. In the range of smaller particles, R⩽1.34 nm the T
c(R) curve is observed to merge with the T
m(R) curve, owing to the disappearance of the work of formation of the crystal surface during crystallization of the melt as
a result of the zero surface tension of CuCl particles of radii commensurate with the thickness of the effective surface layer.
An increase in the size shift of the exciton energy is observed in this same range of CuCl particle radii (1–1.8 nm). The
size dependence of the melting and crystallization temperatures of the nanoparticles is attributed to variation of the free
energy in the surface layer of a particle.
Fiz. Tverd. Tela (St. Petersburg) 41, 310–318 (February 1999) 相似文献
10.
A. B. Lebedev S. A. Pul’nev V. V. Vetrov Yu. A. Burenkov V. I. Kopylov K. V. Betekhtin 《Physics of the Solid State》1998,40(7):1155-1157
The thermal stability of the yield stress and Young’s modulus was investigated in ultrafinegrained copper (99.98%) and a Cu-HfO2 composite obtained by intensive plastic deformation using the method of equichannel angular pressing. It is shown that both
the pure copper and the composite strengthened with HfO2 nanoparticles demonstrate in this state a high yield stress (σ
0.2≈400 MPa). When the two-hour annealing temperature T
a is increased above 200 °C, the yield stress in pure copper decreases to 40 MPa at T
a=400 °C, whereas in the Cu-HfO2 composite, high yield stresses are conserved up to T
a=500 °C. A recovery stage of Young’s modulus is found at around 200 °C both in pure copper and in the Cu-HfO2 composite. It is concluded that this stage reflects the transition of the grain boundaries from a nonequilibrium to an equilibrium
state, and the high-strength properties of the materials are determined mainly by the grain size and depend weakly on the
grain-boundary structure.
Fiz. Tverd. Tela (St. Petersburg) 40, 1268–1270 (July 1998) 相似文献
11.
In the temperature range 15–770°C, a correlation between the dielectric and structural specific features of lead cadmium tungstate
is established. When studying the structure of Pb2CdWO6 in the temperature range 15 ≤ T ≤ 770°C, the unit-cell parameters and atomic parameters of the orthorhombic phase with space group Pmc21 (15 ≤ T ≤ 380°C) and cubic phase with space group Fm3m (380 ≤ T ≤ 770°C) are determined. It is revealed that the antiferroelectric state observed in of Pb2CdWO6 in the orthorhombic phase is associated with antiparallel displacements of Pb atoms. In the cubic phase, the Cd atoms are
found to have disordered static displacements along [100]-type directions. 相似文献
12.
The precipitation of the fcc γ-phase of iron has been studied by a systematic series of isothermal and isochronal (0–48 h)
heat treatments (300–800°C) on a supersaturated solution ofCuFe containing 3 at% Fe. The optimal conditions (450–600°C) for precipitation of the maximum fraction (90%) of iron attainable
within 48 h in the form of γ-Fe have been delineated from analysis of the room temperature spectra. The time dependence for
formation of γ-Fe precipitates is well described by the equation for long term annealing. An activation energyE
a
≈0.6 eV for the formation of γ-Fe in Cu is obtained. It indicates short range rather than long range diffusion in theCuFe sample studied. 相似文献
13.
V. R. Shaginyan 《JETP Letters》1998,68(6):527-533
Fermion condensation (FC) is studied within the density functional theory. FC can fulfill the role of a boundary, separating
the region of strongly interacting electron liquid from the region of strongly correlated electron liquid. Consideration of
the superconductivity in the presence of FC shows that, under certain circumstances, at temperatures above T
c
the superconductivity vanishes and the superconducting gap smoothly transforms into a pseudogap. The pseudogap occupies only
a part of the Fermi surface, and one that shrinks with increasing temperature and vanishes at T=T*, and the single-particle excitations of the gapped area of the Fermi surface have a width γ ∼(T-T
c
).
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 491–496 (25 September 1998)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
14.
D. N. Voskresensky E. E. Kolomeitsev B. Kämpfer 《Journal of Experimental and Theoretical Physics》1998,87(2):211-217
We consider massive photon decay reactions via intermediate states of electron-electron-holes and proton-proton-holes into
neutrino-antineutrino pairs in the course of neutron star cooling. These reactions may become operative in hot neutron stars
in the region of proton pairing where the photon due to the Higgs-Meissner effect acquires an effective mass m
γ
that is small compared to the corresponding plasma frequency. The contribution of these reactions to neutrino emissivity
is calculated; it varies with the temperature and the photon mass as T
3/2
m
γ
7/2
exp(−m
γ
/T) for T<m
γ
. Estimates show that these processes appear as extra efficient cooling channels of neutron stars at temperatures T≅109–1010 K.
Zh. éksp. Teor. Fiz. 114, 385–397 (August 1998)
Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor. 相似文献
15.
S. Vatnik M. C. Pujol J. J. Carvajal X. Mateos M. Aguiló F. Díaz V. Petrov 《Applied physics. B, Lasers and optics》2009,95(4):653-656
The three thermo-optic coefficients of the biaxial laser host KLu(WO4)2 are measured at 633 nm by a deflection method. Their values at 300 K amount to ∂
n
g
/∂
T=−7.4×10−6 K−1; ∂
n
m
/∂
T=−1.6×10−6 K−1 and ∂
n
p
/∂
T=−10.8×10−6 K−1. Nearly athermal propagation directions are found for polarizations along the N
m
and N
p
dielectric axes. 相似文献
16.
R. M. Aseeva P. A. Sakharov A. M. Sakharov 《Russian Journal of Physical Chemistry B, Focus on Physics》2009,3(5):844-850
The paper presents the results obtained in studies of the physicochemical characteristics of modified polysaccharides prepared
by the catalytic oxidation of starch with molecular oxygen in an alkaline medium. The amorphous-crystalline structure of starch
was partially retained after oxidation. The differential scanning calorimetry data were used to determine the specific heat
capacity of oxidized polysaccharides in the vitreous state over the temperature range 10–160°C and the enthalpy and temperature
characteristics of fusion of amorphous-crystalline lamellae. The structural and thermodynamic parameters of crystallites (surface
free energy, enthalpy, and entropy) were calculated. The segmental mobility of oxidized polysaccharide macromolecules and
the transition from the vitreous to high-elasticity state were observed at T
g
= 187.7°C, and the transition to the viscous-flow state, above 209°C. The pyrolysis of the polymer began after the unfreezing
of its segmental mobility and was accompanied by the release of water and carbon dioxide and the formation of a large amount
of coke foam. 相似文献
17.
A. U. Sheleg K. V. Iodkovskaya S. V. Rodin V. A. Aliev 《Physics of the Solid State》1997,39(6):975-977
The influence of γ irradiation on the electrical conductivity σ, the dielectric permittivity ɛ, and the dielectric loss tangent tanδ of β-TlInS2 crystals is investigated in the temperature range of the incommensurate phase. It is established that γ irradiation lowers the values of ɛ and tanδ over the entire investigated temperature range and decreases the maxima of the σ(T) and tanδ(T) curves in the vicinity of the transition temperature T
c, but does not alter the transition temperature.
Fiz. Tverd. Tela (St. Petersburg) 39, 1088–1090 (May 1997) 相似文献
18.
Summary The partition of the spin probe TEMPO between the fluid lipid phase of single-walled vesicles of dipalmitoylphosphatidylcholine
and the aqueous bulk solution have been used to investigate the interaction of monovalent ions with polar head of neutral
phospholipids. The study has been performed by electron spin resonance (ESR) spectroscopy in the temperature range of (20÷60)°C
and in the presence of (0÷3) M 1∶1 electrolyte. In the absence of electrolyte the spin probe TEMPO reveals the characteristic
order→disorder DPPC main phase transition atT
m≈37°C, while the pretransition occurs atT
p≈27.5°C. On increasing the ionic strength of the dispersion medium it results for the partition coefficient,P
C, that, at each temperature,P
C(3)>P
C(2)>P
C(1)>P
C(0). Correspondingly, the pretransition disappears and theT
m value downshifts from ≈37°C with 0 M electrolyte to ≈34°C with 3M salt in the order:T
m(3)>T
m(2)>T
m(1)>T
m(0). The results suggest an increase in the net surface charge density of vesicles due to high ionic-strength values. The
alteration of the electric interactions occurring into the polar zone of DPPC bilayer reduces the hindrances which, in turn,
favour the enhancement of TEMPO partitioning in the hydrophobic core of phospholipid bilayers.
The authors of this paper have agreed to not receive the proofs for correction. 相似文献
19.
Anomalous behavior of the interlayer resistance of a BSCCO-2212 crystal in a parallel magnetic field
V. N. Zavaritskii 《JETP Letters》1996,63(2):139-145
The electrical resistance across the Cu-O layers of a BSCCO-2212 single crystal is investigated in the range of angles 0°⩽φ⩽90°
between the magnetic field H⩽15 T and the ab plane. It is found that the temperature dependence R(T) at the transition into the mixed state is much sharper for φ≃0° than for 1°≲φ≲90°, where R is determined by the perpendicular component of the magnetic field and is described by the Arrhenius law R∼exp(−U/T). For H∥ ab hysteretic jumps in R(T, H), which vanish as the current increases, are observed at fields in the range 5.5⩽H⩽11 T. This effect can be attributed to
a commensurate phase transition in a lattice of Josephson vortices.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 2, 123–128 (25 January 1996) 相似文献
20.
I. A. Smirnov B. I. Smirnov T. S. Orlova Cz. Sulkovski H. Misiorek A. Jezowski J. Muha 《Physics of the Solid State》2011,53(11):2244-2249
This paper reports on measurements of the thermopower S of high-porosity samples of beech wood biocarbon with micron-sized sap pores aligned with the tree growth direction. The
measurements have been performed in the temperature range 5–300 K. The samples have been fabricated by pyrolysis of beech
wood in an argon flow at different carbonization temperatures (T
carb). The thermopower S has been measured both along and across the sap pores, thus offering a possibility of assessing its anisotropy. The curves
S(T
carb) have revealed a noticeable increase of S for T
carb < 1000°C for all the measurement temperatures. This finding fits to the published data obtained for other physical parameters,
including the electrical conductivity of these biocarbons, which suggests that for T
carb ∼ 1000°C they undergo a phase transition of the insulator-(at T
carb < 1000°C)-metal-(at T
carb > 1000°C) type. The existence of this transition is attested also by the character of the temperature dependences S(T) of beech wood biocarbon samples prepared at T
carb above and below 1000°C. 相似文献