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1.
Results are presented of experimental studies of how the spontaneous polarization of β-BaB2O4 (BBO) varies with temperature in the range from 2.5 to 90 K. Values of the pyroelectric coefficient γ
s are calculated, and effective values of the Debye temperature (Θ=112 K) and the Einstein temperature (ΘE=28 K) are estimated. It is shown that the dominant contribution to γ
s comes from acoustic lattice modes. A mechanism is proposed to explain why the temperature dependence of the pyroelectric
effect in linear pyroelectric materials is different from that in ferroelectrics.
Fiz. Tverd. Tela (St. Petersburg) 39, 1631–1633 (September 1997) 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.
A. H. Cai X. Xiong Y. Liu H. Chen W. K. An X. S. Li Y. Zhou Y. Luo 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(2):147-151
We propose expressions for the estimation of the isenthalpic temperature T
0 (T
0 = αT
m
, α is a semi-empirical parameter and 0 ⩽ α < 1, T
m
is the solidus temperature) and the Kauzmann temperature T
k
(T
k
= T
m
exp(α−1)) for glass forming alloys. It is found that T
k
estimated by T
k
= T
m
exp(α−1) is in agreement with that directly calculated from the heat capacity data, indicating that T
k
= T
m
exp(α − 1) can be used to estimate T
k
of glass forming alloys. T
0 estimated by T
0 = αT
m
, on the other hand, widely deviates from that of directly calculated from the heat capacity data. This suggests that the
enthalpy difference of the under-cooled liquid and the crystal might be a nonlinear function of the temperature below T
k
. Moreover, the Gibbs free energy difference ΔG is not sensitive to the deviation of α. 相似文献
4.
The Young’s modulus and the internal friction of beryllium polycrystals (size grain from 6 to 60 μm) prepared by the powder
metallurgy method have been studied as functions of the amplitude and temperature in the range from 100 to 873 K. The measurements
have been performed using the composite piezoelectric vibrator method for longitudinal vibrations at frequencies about 100
kHz. Based on the acoustic measurements, the data have been obtained on the elastic and inelastic (microplastic) properties
as functions of vibration stress amplitudes within the limits from 0.2 to 30–60 MPa. The microplastic deformation diagram
is shown to become nonlinear at the amplitudes higher than 5 MPa. The beryllium mechanical characteristics (the yield strength
σ
0.2, the ultimate strength σ
u
, and the conventional microscopic yield strength σ
y
) obtained with various grain sizes are compared. At room temperature, all the parameters satisfactorily obey the Hall-Petch
relationship, although there is no complete similarity. The temperature dependences are quite different, namely: σ
0.2(T) and σ
u
(T) decrease monotonically during heating from room temperature to higher temperatures; however, σ
y
(T) behaves unusually, and it has a minimum near 400 K. The different levels of stresses and the absence of similarity indicate
that the scattering of the ultrasound energy and the formation of a level of the macroscopic flow stresses in beryllium occur
on dislocation motion obstacles of different origins. 相似文献
5.
M.?P.?Ivliev S.?I.?Raevskaya O.?Yu.?Kravchenko I.?P.?Raevski? L.?A.?Reznichenko 《Physics of the Solid State》2009,51(10):2109-2114
It is established that the Curie-Weiss temperature of Na1 − x
Li
x
NbO3 solid solutions determined by extrapolation of linear portions of the temperature dependence of the reciprocal of the permittivity
ɛ−1 from the cubic phase sharply increases with x, although the temperature of the ɛ(T) maximum decreases. It is shown in terms of a simple theoretical model that the experimentally observed change in the dielectric
properties of Na1 − x
Li
x
NbO3 is well explained under the assumption of formation of a dipole system due to the displacement of Li cations from the center
of the cubooctahedral cavity because of the significant steric misfit between the Na and Li cations. 相似文献
6.
Anderson Rosa Kurelo Yuri Aparecido Opata Lincoln Brum de Leite Gusmão Pinheiro Alcione Roberto Jurelo Adilson Luiz Chinelatto 《Brazilian Journal of Physics》2011,41(1):1-6
We report on systematic conductivity fluctuation measurements on samples of Ho1 − x
Ce
x
Ba2Cu3O7 − δ
with x = 0.00, 0.05, and 0.10. The samples were produced by a standard solid-state reaction method, and the microstructure was analyzed
by X-ray diffraction. To identify power-law divergences of the conductivity, the results were analyzed in terms of the temperature
derivative of the resistivity dρ/dT and with the logarithmic derivative of the conductivity with respect to temperature − dln (Δσ)/dT. It was observed that the critical temperature decreases and that the transition width increases with increasing Ce doping.
The data showed the occurrence of a two-stage transition besides the pairing transition splitting, associated with Ce doping
and related with the occurrence of a phase separation. Above the critical temperature, the Gaussian and critical regimes were
observed. On approaching the zero resistance state, our results showed a power-law behavior that corresponds to a phase transition
from a paracoherent to a coherent state of the granular array. 相似文献
7.
X. G. Tang Q. X. Liu J. Wang H. L. W. Chan 《Applied Physics A: Materials Science & Processing》2009,96(4):945-952
The effect of a dc bias field on the diffuse phase transition and nonlinear dielectric properties of sol-gel derived Ba(Zr0.2Ti0.8)O3 (BZT) ceramics are investigated. Diffuse phase transitions were observed in BZT ceramics and the Curie–Weiss exponent (CWE)
was γ∼2.0. The dielectric constant versus temperature characteristics and the γ in the modified Curie–Weiss law, ε
−1=ε
m
−1[1+(T−T
m
)
γ
/C1](1≤γ≤2), as a function of the dc bias field was obtained for BZT ceramics. The results indicated that γ is a function of dc bias field, and the γ value decreased from 2.04 to 1.73 with dc bias field increasing from 0 to 20 kV/cm. The dielectric constant decreases with
increasing dc bias field, indicating a field-induced phase transition. The dc bias field has a strong effect on the position
of the dielectric peak and affects the magnitude of the dielectric properties over a rather wide temperature range. The peak
temperature of the dielectric loss does not coincide with the dielectric peak and an obvious minimum value for the dielectric
loss at the temperature of the dielectric peaks is observed. At room temperature, 300 K, the high tunability (K=80%), the low loss tangent (≈0.01) and the large FOM (74), clearly imply that these ceramics are promising materials for tunable capacitor-device applications. 相似文献
8.
A. Yu. Mollaev I. K. Kamilov R. K. Arslanov T. R. Arslanov U. Z. Zalibekov V. M. Novotortsev S. F. Marenkin 《JETP Letters》2010,91(9):478-480
The magnetic susceptibility χ/χ0 and the longitudinal Δρ
zz
/ρ0 and transverse Δρ
xx
/ρ0 magnetoresistances have been measured as functions of the hydrostatic pressure P ≤ 7 GPa at room temperature in the high-temperature ferromagnetic semiconductor Cd0.7Mn0.3GeAs2 with a chalcopyrite structure and the Curie temperature T
c = 355 K. A pressure-induced metamagnetic transition from the low-magnetization state to the high-magnetization state has
been observed in Cd0.7Mn0.3GeAs2 near the magnetic ordering temperature. This transition is accompanied by the hysteresis of the magnetic susceptibility and
magnetoresistance. 相似文献
9.
A. Geranios 《Il Nuovo Cimento C》1989,12(5):613-624
Summary The dynamical characteristics of α-particles in the solar wind between 0.3 and 1.0 AU are studied. It has been found that
the connections between alpha temperature and speed, normalized at 1AU, as well as radial temperature exponents significantly
differ from those found for protons. Between α and proton temperature, generally, the α temperature depends stronger on flow
speed. Nevertheless, the flow characteristics of alphas and protons concerning their speeds are similar. For example, the
dependence ofT
α onV
α is stronger also for slow than for fast alpha flows. The alpha radial temperature decreases much slower than proton temperature
away from the Sun, according to the relationT
α/T
0=(r/r
0)−k
withk varying from very low (0.10) to moderate values (0.60).T
α,T
0 are the alpha temperatures at distancesr,r
0(=1 AU), respectively. These findings strongly suggest an additional heating of alphas, for example by Alfven waves or Coulomb
collisions.
To speed up publication, the author of this paper has agreed to not receive the proofs for correction. 相似文献
10.
Fan Yu-shan Song Hong-zhang Li Zhi-hui Yang De-lin Hu Xing 《Frontiers of Physics in China》2006,1(3):368-370
The oxygen adsorption-desorption properties of RBa2Cu3O7−δ
(R = Gd, Er, Eu, Dy, Sm, Ho and Nd) and Y1−x
LaxBa2Cu3O7−δ
(x=0.1, 0.5 and 1.0) were investigated from room temperature to 950 °C by thermogravimetry (TG). The results show that all samples
will release oxygen with the increasing of temperature and the released oxygen can be absorbed back into the sample when temperature
decreases. However, dependent on the rare earth element, the amount of the released oxygen is different for these samples.
Moreover, in the temperature increasing and decreasing circle the repetition of oxygen adsorption-desorption is also different. 相似文献
11.
Bi4V2O11 exists in three phases viz. α, β, and γ. High temperature γ-phase can be stabilized to room temperature owing to its higher
conductivity by the partial substitution of metallic cations for vanadium in Bi4V2O11. Phase transitions from α → β and β → γ are composition and temperature-dependent. Mn2+-doped compounds Bi4V2−x
Mn
x
O11−
δ
(0 ≤ x ≤ 0.4) have been synthesized by solid state reaction technique and investigated by X-ray diffraction and ionic conductivity
measurement. High ionic conducting γ-phase is stabilized for x ≥ 0.2. The ionic conductivity of the series of Bi4V2−x
Mn
x
O11−
δ
samples has been measured by using ac impedance spectroscopy technique. The conductivity data do show departure from its
simple Arrhenius behavior for all of the compositions. The highest conductivity observed for x = 0.2 sample can be attributed to lower activation energy. 相似文献
12.
A. U. Sheleg E. M. Zub L. A. Stremoukhova A. M. Luginets 《Physics of the Solid State》1997,39(6):932-934
The lattice parameters a and c of β-BaB2O4 crystals have been measured in the temperature range 80–300 K by the x-ray diffraction method. The thermal expansion coefficients
α are calculated from the measured values of the parameters. A substantial anisotropy of the thermal expansion is found. It
is shown that the thermal expansion coefficient α
c along the c axis is an order of magnitude greater than the thermal expansion coefficient α
a in a plane perpendicular to this axis. It is established that α
a becomes negative in the temperature range 80–190 K.
Fiz. Tverd. Tela (St. Petersburg) 39, 1038–1040 (June 1997) 相似文献
13.
V. Yu. Yushankhai 《Hyperfine Interactions》1989,50(1-4):775-779
On the basis of current theoretical views on the critical phenomena in isotropic Heisenberg ferromagnets the power temperature
behavior Λ=c(τ)λ0τ-w has been derived for the muon spin relaxation rate Λ as π-T
c
−1
(T-T
c
) → 0+. It is shown that the crossover from an exchange critical regime to a dipolar one is accompanied not only with the change
in the critical exponentw in the above law, but also with the reduction of the coefficientc(π). A comparison with the temperature behaviour of the inverse nuclear relaxation timet
R
−1
measured in the PAC experiment is carried out. 相似文献
14.
A. A. Petukhov B. E. Zhurtanov S. S. Molchanov N. D. Stoyanov Yu. P. Yakovlev 《Technical Physics》2011,56(4):520-525
The electroluminescent characteristics of an InGaAsSb/GaAlAsSb heterostructure LED emitting at 1.85 μm are studied in the
temperature range 20–200°C. It is shown that the emission power exponentially drops as P ≅ 0.4exp(2.05 × 103/T) with a rise in temperature primarily because of an increase in the Auger recombination rate. It is found that band-to-band
radiative recombination goes in parallel with recombination through acceptor levels, the latter causing the emission spectrum
to broaden. With a rise in temperature, the activation energy of the acceptor levels decreases by the law ΔE≅ 32.9 − 0.075T and the maximum of the LED’s emission spectrum shifts toward the long-wavelength range (hν
max = 0.693 − 4.497 × 10−4
T). Based on the dependence E
g
= hν
max − 0.5kT and experimental data, an expression is derived for the temperature variation of the bandgap in the In0.055Ga0.945AsSb active area, E
g
≅ 0.817 − 4.951 × 10−4
T, in the range 290 K < T < 495 K. The resistance of the heterostructure decreases exponentially with rising temperature as R
0 ≅ 5.52 × 10−2exp(0.672/2kT), while cutoff voltage U
cut characterizing the barrier height of a p−n junction decreases linearly with increasing temperature (U
cut = −1.59T + 534). It is found that the current through the heterostructure is due to the generation-recombination mechanism throughout
the temperature interval. 相似文献
15.
N. V. Dalakova B. I. Belevtsev A. S. Panfilov E. Yu. Belyaev 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(5):692-694
The temperature dependence of the resistance of a La2CuO4 + δ (δ ≈ 0.05) single crystal with the Neel temperature T
N ≈ 205 K was investigated in order to establish the correlation between the transport and magnetic properties of the crystal.
The R(T) dependence near T
N reveals a kink related to the enhancement of sample’s conductivity upon the transition from the antiferromagnetic to paramagnetic
state. With an increase in temperature far above T
N, the transition from the dielectric (dR/dT < 0) to metal (dR/dT > 0) occurs. The observed behavior of resistance is attributed to delocalization of carriers above T
N. 相似文献
16.
I. V. Zolotukhin S. V. Spitsina L. I. Yanchenko L. N. Korotkov 《Physics of the Solid State》1999,41(11):1891-1893
Macroscopic fractal aggregates of KH2PH4 (KDP) measuring up to 500 μm have been obtained. The fractal structure forms as a result of the precipitation of KDP particles
from a supersaturated aqueous solution in the presence of a temperature gradient followed by a diffusioncontrolled mechanism
of aggregation. The electron-microscopic analysis performed has shown that the fractals are formed predominantly from crystallites
of the tetragonal modification measuring ∼1 μm. The dielectric constant (ɛ) of fractal KH2PO4 has been measured in the temperature range 80–300 K. A characteristic anomaly has been discovered on the ɛ(T) curve in the vicinity of 122 K, which attests to a ferroelectric phase transition. The absolute value of ɛ is significantly smaller than the components ɛ
11 and ɛ
33 for KH2PO4.
Fiz. Tverd. Tela (St. Petersburg) 41, 2059–2061 (November 1999) 相似文献
17.
The behavior of the thermal conductivity k(T) of bulk faceted fullerite C60 crystals is investigated at temperatures T=8–220 K. The samples are prepared by the gas-transport method from pure C60, containing less than 0.01% impurities. It is found that as the temperature decreases, the thermal conductivity of the crystal
increases, reaches a maximum at T=15–20 K, and drops by a factor of ∼2, proportional to the change in the specific heat, on cooling to 8 K. The effective phonon
mean free path λ
p, estimated from the thermal conductivity and known from the published values of the specific heat of fullerite, is comparable
to the lattice constant of the crystal λ
p∼d=1.4 nm at temperatures T>200 K and reaches values λp∼50d at T<15 K, i.e., the maximum phonon ranges are limited by scattering on defects in the volume of the sample in the simple cubic
phase. In the range T=25−75 K the observed temperature dependence k(T) can be described by the expression k(T)∼exp(Θ/bT), characteristic for the behavior of the thermal conductivity of perfect nonconducting crystals at temperatures below the
Debye temperature Θ (Θ=80 K in fullerite), where umklapp phonon-phonon scattering processes predominate in the volume of the
sample.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 651–656 (25 April 1997) 相似文献
18.
A. T. Pugachev N. P. Churakova N. I. Gorbenko Kh. Saadli E. S. Syrkin 《Journal of Experimental and Theoretical Physics》1998,87(5):1014-1018
The thermal expansion coefficient a and structure of C60 films with thickness t∼3–10 nm were investigated in the temperature interval from room to liquid-nitrogen temperature by electron-optical methods.
The thermal expansion coefficient was determined from the temperature shift of the diffraction maxima in the electron diffraction
patterns. The objects of investigation were epitaxial C60 films condensed in vacuum on a (100) NaCl cleavage surface and oriented in the (111) plane. A surface-induced size effect
in the thermal expansion coefficient was observed. It was established that as t decreases α
f increases and is described well by the relation α
f=17·10−6 K−1+8.3·10−5 nm K−1
t
−1. This relation was used to estimate the linear expansion coefficient α
s of the C60 surface in the (111) plane as α
s=60·10−6K−1, which is several times larger than the bulk value. The experimental results agree satisfactorily with the theoretical calculations
of the mean-square displacements of molecules located in a region near the surface.
Zh. éksp. Teor. Fiz. 114, 1868–1875 (November 1998) 相似文献
19.
R. Gammag C. Villagonzalo 《The European Physical Journal B - Condensed Matter and Complex Systems》2012,85(1):22
The effect of atomic disorder on the electron transport and the magnetoresistance (MR) of Co2CrAl Heusler alloy (HA) films has been investigated. We show that Co2CrAl films with L21 order exhibit a negative value for the temperature coefficient of resistivity (TCR) in a temperature range of 10 < T < 290 K, and the temperature dependence of electric conductivity varies as T
3/2 similarly to that of the zero-gap semiconductors. The atomic or the site disorder on the way of L21 → B2 → A2 → amorphous state in Co2CrAl HA films causes the deviation from this dependence: reduction in the absolute value of TCR as well as decrease in the
resistivity down to ϱ(T = 293 K) ∼ 200 μΩ cm in comparison to ϱ(T = 293 K) ∼ 230 μΩ cm typical for the Co2CrAl films with L21 order. The magnetic-field dependence of MR of the Co2CrAl films with L21 order is determined by two competing contributions: a positive Lorentz scattering and a negative s-d scattering. The atomic disorder in Co2CrAl films drastically changes MR behavior due to its strong influence on the magnetic properties. 相似文献
20.
A. A. Verevkin N. G. Ptitsina K. V. Smirnov G. N. Gol’tsman E. M. Gershenzon K. S. Ingvesson 《JETP Letters》1996,64(5):404-409
The temperature dependence of the energy relaxation time τe (T) of a two-dimensional electron gas at an AlGaAs/GaAs heterointerface is measured under quasiequilibrium conditions in the
region of the transition from scattering by acoustic phonons to scattering with the participation of optical phonons. The
temperature interval of constant τe, where scattering by the deformation potential predominates, is determined. In the preceding, low-temperature region, where
piezoacoustic and deformation-potential-induced scattering processes coexist, τ e decreases slowly with increasing temperature. Optical phonons start to participate in the scattering processes at T∼25 K (the characteristic phonon lifetime was equal to τLOτ4.5 ps). The energy losses calculated from the τe data in a model with an effective nonequilibrium electron temperature agree with the published data obtained under strong
heating conditions.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 5, 371–375 (10 September 1996) 相似文献