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1.
The thermally stimulated depolarization currents of poly (ethylene-terephthalate) electrets with a reduced degree of crystallinity
(≃4%), corona-charged at polarization temperatures between 65 and 100 °C, show a heteropolar α * relaxation placed between the α relaxation (heteropolar) and the ρ relaxation (homopolar). This α * relaxation is associated with a uniform mechanism and has been observed in the discharge of electrets with shorted evaporated
electrodes, which have been formed using the windowing polarization method at polarization temperatures between 76 and 79
°C. The intensity and position of α * depend on the degree of crystallinity and the morphology. The application of the method of thermal stimulation by steps,
which leads to a gradual crystallization of the sample, shows that the α c relaxation of crystalline PET has its origin in α *. 相似文献
2.
Electrical and superconducting properties of indium films condensed in a H 2 atmosphere (pressure p
H
2=6×10 −6 to 1.4×10 −4 Torr) onto a substrate cooled with liquid helium are investigated. As hydrogen content is increased, a continuous increase
in residual resistivity ρ* is observed, permitting systematic study of the resistance vs. temperature dependence R( T) and the superconducting transition temperature T
c on approaching the metal-insulator transition (MIT). With regard to ρ*, four regimes of conductivity can be observed: (1)
conductivity with a positive temperature resistance coefficient (TRC), (2) conductivity with a small, constant, negative TRC,
(3) conductivity under weak localization with Δ R ( T) ∼ ln T or
type corrections, (4) hopping conductivity. T
c rises continuously with ρ* and reaches its peak (∼5.2K) in the second regime. A further increase of ρ* leads to a decrease
of T
c and complete suppression of superconductivity. The experimental dependence R( T) is compared with theory. The T
c variation on approaching the MIT and the relation between Mooij's rule and the superconducting properties are discussed. 相似文献
3.
The isochoric heat capacity of pure methanol in the temperature range from 482 to 533 K, at near-critical densities between
274.87 and 331.59 kg· m −3, has been measured by using a high-temperature and high-pressure nearly constant volume adiabatic calorimeter. The measurements
were performed in the single- and two-phase regions including along the coexistence curve. Uncertainties of the isochoric
heat capacity measurements are estimated to be within 2%. The single- and two-phase isochoric heat capacities, temperatures,
and densities at saturation were extracted from experimental data for each measured isochore. The critical temperature ( Tc = 512.78±0.02K) and the critical density (ρ c = 277.49±2 kg · m −3) for pure methanol were derived from the isochoric heat-capacity measurements by using the well-established method of quasi-static
thermograms. The results of the CVVT measurements together with recent new experimental PVT data for pure methanol were used to develop a thermodynamically self-consistent Helmholtz free-energy parametric crossover
model, CREOS97-04. The accuracy of the crossover model was confirmed by a comprehensive comparison with available experimental
data for pure methanol and values calculated with various multiparameter equations of state and correlations. In the critical
and supercritical regions at 0.98 Tc≤ T ≤ 1.5 Tc and in the density range 0.35ρ c ≤ ρ leq 1.65 ρ c, CREOS97-04 represents all available experimental thermodynamic data for pure methanol to within their experimental uncertainties. 相似文献
4.
Poly(ethylene-2,6-naphthalate) (PEN) was crystallized from the glassy state at atmospheric pressure (beyond the end of primary crystallization) and from the melt at high pressure. The structure was characterized using small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC) and density measurements. The SAXS patterns were analysed using the interface distribution function (IDF) method. For the materials prepared at ambient pressure the crystallinity inside the layer stacks remains nearly constant during the secondary crystallization process. On the other hand, the volume filled with the stacks increases as a function of crystallization temperature ( T
c) and time ( t
c). For T
c > 200°C secondary crystallisation goes along with a dynamic rearrangement of the primary stacks, as concluded from variations of the layer thickness distributions in the SAXS data. For T
c < 200°C primary lamellae are stable, and both insertion of new crystal lamellae into existing stacks and generation of additional stacks is found. In contrast to PET, two different kinds of layer stacks are not observed in the PEN nano-composites. Materials prepared at 400 MPa exhibit high roughness of the crystalline domain surfaces. Depending on T
c there is a continuous transformation from the to the -crystal modification, but hardly any change of the long period. Crystal thickness increases, both at the expense of the amorphous thickness and of the volume filled with lamellar stacks. The structure of samples showing two melting peaks is discussed in terms of a dual lamellar contribution of correlated and uncorrelated nano-crystallites, respectively. 相似文献
5.
We present measurements of the field induced changes in the 47 GHz complex resistivity, Δρ~( H, T), in Tl 2Ba 2CaCu 2O 8+x
(TBCCO) thin films with T
c
≃ 105 K, prepared on CeO 2 buffered sapphire substrates. At low fields (μ 0
H < 10 mT) a very small irreversible feature is present, suggesting a little role of intergranular phenomena. Above that level
Δρ~( H, T exhibits a superlinear dependence with the field, as opposed to the expected (at high frequencies) quasilinear behaviour.
We observe a crossover between predominantly imaginary to predominantly real (dissipative) response with increasing temperature
and/or field. In addition, we find the clear scaling property Δρ~( H, T = Δρ~[ H/ H
* ( T)], where the scaling field H
∗ ( T) maps closely the melting field measured in single crystals. We discuss our microwave results in terms of loss of flux lines
rigidity. 相似文献
6.
We have studied the effect of atomic ordering in a nanodimensional clustered structure of amorphous LaSrMnO films on the slope
of the temperature dependence of resistivity ρ( T) in the regions where dρ/ dT > 0. It is established that a high concentration of clusters of a “metallic” phase ( C
met = 9%) capable of fertromagnetic ordering leads to a giant temperature coefficient of resistivity (TCR), with its value (normalized
slope) reaching ( dρ/ dT)/ρ = 1.6 × 10 4% K −1. Samples with a small concentration of such clusters ( C
met = 0.1%) possess paramagnetic properties and their normalized TCR decreases by three orders of magnitude to ( dρ/ dT)/ρ = 1.7 × 10 1% K −1. This behavior is explained by self-consistent changes in the atomic, magnetic, and electron subsystems. 相似文献
7.
The effect of magnetic iron impurity on the superconducting properties of amorphous Nb 50Zr 35−x
Si 15Fe
x
( x⩽4 at %) alloys was examined. Doping with an iron impurity resulted in a linear depression of T
c and H
c2( T) and a decrease in
and ρ
n after reaching a maximum value at 0.5 to 1.0 at % iron. The observed decrease was about 35% for T
c, 85% for H
c2 at 2.0 K, 16% for
and 21% for ρ
n. Although the decrease in
occurs through the decrease in ρ
n as expected from the GLAG theory, the depression in T
c caused by magnetic impurity could not be explained in terms of the GLAG theory which is applicable to Nb-Zr-Si amorphous
alloys without magnetic impurity, but was interpreted as arising from the pair-breaking effect in the superconducting nature
due to magnetic scattering. However, the pair-breaking effect was found to be smaller by about one-tenth for the present amorphous
superconductors than for crystalline superconductors, indicating the high stability of the superconductivity of the Nb-Zr-Si-Fe
alloys against the magnetic scattering arising from the magnetic impurity. The reduced magnetic field at which the reduced
fluxoid pinning force exhibits a maximum value increased with iron concentration, indicative of an enhancement of fluxoid
pinning force. The enhancement in fluxoid pinning force was interpreted as arising from the increase in compositional, electronic
and/or magnetic fluctuations by the dope of iron impurity. 相似文献
8.
The lattice parameters of film-grade poly(phenylene sulphide), PPS, have been studied at room temperature as a function of thermal history. Effects of crystallization temperature and annealing time for films crystallized from the rubbery amorphous state were investigated using wide- and small-angle X-ray diffraction, bulk density and thermal analysis techniques. The dimensions of the crystal lattice are found to depend upon prior thermal treatment conditions. As the cold crystallization temperature, T
c, increases, or the annealing time at fixed temperature increases, the bulk density, degree of crystallinity, and crystal perfection increase. With an increase in annealing time at fixed temperature, lattice a, b, and c decrease leading to an increase in lattice density. As the cold crystallization temperature increases, lattice density also increases as a result of a systematic decrease in lattice parameters a and b. 相似文献
9.
The present paper deals with the theoretical investigation of temperature-dependent resistivity of the perovskite manganites
La 0.78Pb 0.22MnO 3-δ within the framework of the classical electron–phonon model of resistivity, i.e., the Bloch–Gruneisen model. Due to inherent
acoustic (low-frequency) phonons (ω ac) as well as high-frequency optical phonons (ω op), the contributions to the electron–phonon resistivity have first been estimated. At low temperatures the acoustic phonons
of the oxygen-breathing mode yield a relatively larger contribution to the resistivity as compared to the contribution of
optical phonons. Furthermore, the nature of phonons changes around T = 215 K exhibiting a crossover from an acoustic to optical phonon regime with elevated temperature. The contribution to resistivity
estimated by considering both phonons, i.e., ω ac and ω op, when subtracted from experimental data, infers a T4.5 temperature dependence over most of the temperature range. Deduced T4.5 temperature dependence of ρdiff = [ ρexp − { ρ0 + ρe-ph( = ρac + ρop)}] is justified in terms of electron–magnon scattering within the double exchange (DE) process. Within the proposed scheme,
the present numerical analysis of temperature dependent resistivity shows similar results as those revealed by experiments 相似文献
10.
The specific contact resistance of the screen-printed Ag contacts in the silicon solar cells has been investigated by applying
two independent test methodologies such as three-point probe (TPP) and well-known transfer length model (TLM) test structure
respectively. This paper presents some comparative results obtained with these two measurement techniques for the screen-printed
Ag contacts formed on the porous silicon antireflection coating (ARC) in the crystalline silicon solar cells. The contact
structure consists of thick-film Ag metal contacts patterned on the top of the etched porous silicon surface. Five different
contact formation temperatures ranging from 725 to 825 °C for few minutes in air ambient followed by a short time annealing
step at about 450 °C in nitrogen ambient was applied to the test samples in order to study the specific contact resistance
of the screen-printed Ag metal contact structure. The specific contact resistance of the Ag metal contacts extracted based
on the TPP as well as TLM test methodologies has been compared and verified. It shows that the extraction procedure based
on the TPP method results in specific contact resistance, ρ
c
= 2.15 × 10 −6 Ω-cm 2 indicating that screen-printed Ag contacts has excellent ohmic properties whereas in the case of TLM method, the best value
of the specific contact resistance was found to be about ρ
c
= 8.34 × 10 −5 Ω-cm 2. These results indicate that the ρ
c
value extracted for the screen-printed Ag contacts by TPP method is one order of magnitude lower than that of the corresponding
value of the ρ
c
extracted by TLM method. The advantages and limitations of each of these techniques for quantitatively evaluating the specific
contact resistance of the screen-printed Ag contacts are also discussed. 相似文献
11.
The effects of the annealing of 20BaO–30V 2O 5–50Bi 2O 3 glass on the structural and electrical properties were studied by scanning electron micrographs (SEM), X-ray diffraction (XRD), differential scanning calorimeter (DSC) density ( d) and dc conductivity ( σ). The XRD and SEM observations have shown that the sample under study undergoes structural changes: from amorphous at the beginning, to partly crystalline after nanocrystallization at crystallization temperature ( Tc) for 1 h and to colossal crystallization after the annealing at the same temperature for 24 h. The average size of these grains after nanocrystallization at Tc for 1 h was estimated to be about 25–35 nm. However, the glass heat treated at Tc = 580 °C for 24 h the microstructure changes considerably. The nanomaterials obtained by nanocrystallization at Tc for 1 h exhibit giant improvement of electrical conductivity up to four order of magnitude and better thermal stability than the as-received glass. The major role in the conductivity enhancement of this nanomaterial is played by the developed interfacial regions “conduction tissue” between crystalline and amorphous phases, in which the concentration of V 4+–V 5+ pairs responsible for electron hopping is higher than inside the glassy matrix. The annealing at Tc for 24 h leads to decrease of the electronic conductivity. This phenomena lead to disappearance of the abovementioned “conduction tissue” for electrons and substantial reduction of electronic conductivity. The high temperature (above θ/2) dependence of conductivity could be qualitatively explained by the small polaron hopping (SPH) model. The physical parameters obtained from the best fits of this model are found reasonable and consistent with the glass compositions. 相似文献
12.
Following the previous recognition [1], reached with the aid of real time low angle X-ray diffraction (using a synchrotron X-ray source) that in melt crystallized polyethylene the initial (primary) lamellar thickness is much smaller than hitherto envisaged, we have proceeded to construct the full relationship between primary fold length ( I
g
*) and supercooling ( T) covering a wide range of crystallization temperature ( T
c). The principal result of this work is the identification of supercooling as the sole factor which determines I
g
*. Comparison with crystallization from solution [2–4] has revealed that the I
g
* against T curves are completely superposable thus removing the gap which has existed up to the present between melt and solution crystallization, bringing about a welcome unification of these two separate (at least as far as fold length was concerned) aspects of polymer crystallization. Further, we show that while T determines I
g
*, subsequent thickening is determined by the absolute temperature. Isothermal thickening in particular proceeds first by a large discontinuous step followed by a continuous logarithmic increase with time. The importance of these findings and in particular the affirmation of the unique role of supercooling for chain folding and lamellar crystallization in general is emphasized. 相似文献
13.
In order to optimize the series array performance of Y Ba 2Cu 3O 7−x (YBCO) grain boundary shunted junctions, a method to determine and control the junction resistance R s and Au/YBCO contact resistivity ρ
c
has been developed. 200 nm thick c-oriented YBCO films were grown by intermittent thermal coevaporation on bicrystal yttria-stabilized
zirconia substrates. A gold contact overlayer of thickness d n was deposited in situ. Normal junction resistances have been measured as a function of d n and shunt width w. It was shown that, in accordance with theoretical estimates, the junction shunt resistance is essentially
controlled by the c-axis Au/YBCO interface specific resistance and scales as
. The product ρ
c
ρ
n
≃ 3.10 −14 Ω 2
cm
3 was estimated from the experimental data, leading to ρ
c
≈ 10 −8 Ω cm
2 for typical values of ρ
n
for gold thin films. 相似文献
14.
The structure of phases and interphases in samples crystallized under controlled undercoolings, of isotactic polypropylene/ethylene-co-propylene
copolymers (iPP/EPR blends) was examined using optical and electron microscopy and small-angle X-ray scattering and differential
scanning calorimetry. The study was undertaken to establish the influence of molecular structure of the EPR copolymers and
blend composition on the phase structure developed in samples isothermally crystallized at relatively low undercoolings. Optical
and electron microscopy revealed that the molecular structure and composition of the EPR phase play a predominant role in
determining the mode and state of dispersion of the minor rubber component. It was also found that the crystallization process
of iPP from its blends was influenced by the presence of the EPR phase with no regular dependence on its molecular structure
and composition. For a given crystallization temperature, a decrease in thickness of the crystalline lamellae, L
c, and an increase in the amorphous interlamellar layer, L
a were observed. The L
c and L
a values were found to be strictly related to the blend composition; L
c decreasing and L
a increasing with increasing EPR content in the blend. 相似文献
15.
This work develops the Helmholtz potential A(ρ, T) for He 4 below 0.8 K. Superfluid terms, related to temperature and momentum gradients, are neglected with negligible loss of accuracy
in the derived state properties (specific heats, first sound velocity, expansivity, compressibility, etc.). Retained terms
are directly related to a bulk fluid compressibility plus phonon and roton excitations in this quantum fluid. The bulk fluid
compressibility is found from the empirical equation c 13 ≈ c 103 + b; P, where c1 is the velocity of first sound, P is the pressure, and c10 and b are constants; this empirical equation is found to apply also to other helium temperature ranges and to other fluids. The
phonon excitations lead to a single temperature-dependent term in A(ρ , T) up to 0.3 K, with only two more terms added up to 0.8 K. The roton potential, negligible below about 0.3 K, is a single
term first derived 60 years ago but little used in more recent work. The final A(ρ , T) is shown to fit available experimental specific heat data to about ±2% or better. The magnitude of the pressure-independent
Gruneisen parameter below 0.3 K is typical of highly compressed normal liquids. Extension of the equation above 0.8 K is hampered
by lack of data between 0.8 and 1.2 K 相似文献
16.
A novel amorphous structure coupling with ultra-fine nano α-Fe grains in the surface crystallization layer was fabricated successfully through composition regulation and proper quenching conditions. The microstructure of the newly formed surface crystallization layer and its effects on soft magnetic properties of FeMnCuMoCPSiB amorphous alloy were investigated systematically. The FeMnCuMoCPSiB amorphous alloy with surface α-Fe crystallization layers exhibits an excellent comprehensive performance of soft magnetic properties (SMPs) with high Bs of 1.67 T, low Hc of 1.6 A/m, and high μi of 9.3?×?103 at 1 kHz. The SMPs of the amorphous alloy is considerably superior to that of widely used commercial soft magnetic materials METGLAS 2605, promising a potential engineering application. It is noteworthy that a nanoscale surface precipitation was found in the alloy, which favors SMPs of the alloy. 相似文献
17.
The SEM and specific contact resistance measurements of the Ag metal contact formed by applying a fire-through process on
the shallow emitter region of the silicon solar cell have been investigated. The metal contact consists of screen-printed
Ag paste patterned on the silicon nitride (Si 3N 4) deposited over the n +-Si emitter region of the solar cell. The sintering step consists of a rapid firing step at 800 °C or above in air ambient.
This is followed by an annealing step at 450 °C in nitrogen ambient. It enables to drive the Ag metal paste onto the Si 3N 4 layer and facilitates the formation of an Ag metal/p-Si contact structure. It serves as the top metallization for the screen-printed
silicon solar cell. The SEM measurement shows that sintering of the Ag metal paste at 800 °C or above causes the Ag metal
to firmly coalesce with the underlying n +-Si surface. A thin layer of conductive glassy layer is also presents at the interface of the Ag metal and n +-Si surface. The electrical quality of the contact structure was characterized by measuring the specific contact resistance,
ρ
c
(in Ω-cm 2) using the iteration technique based on the power loss calculation for the solar cell. It shows that best value of ρ
c
= 2.53 × 10 −5 Ω-cm 2 is estimated for the Ag metal contact sintered at temperature above 800 °C. This value of ρ
c
is two orders of magnitude lower than the typical value of ρ
c
= 3 × 10 −3 Ω-cm 2 reported previously for the Ag contacts of the solar cell. Such low value of ρ
c
for the Ag metal contacts indicates that fire-through process results in excellent ohmic properties. The plot of the ρ
c
versus impurity doping level ( N
s
) shows that measured value of the ρ
c
follows a linear relationship with the N
s
as predicted by the theory for the heavily doped semiconductor surface. Hence, carrier injection across the Schottky barrier
height is quite appropriate to explain the observed ohmic properties of the Ag metal contacts on the n +-Si surface of the silicon solar cell.
相似文献
18.
The van der Waals equation for a monomer is used to derive the equation of state for a fluid consisting of chain molecules
of equal length. The evolution of a part of the diagram of state pertaining to liquid-vapor equilibrium is treated for the
case of an increase in the number of links in a molecule. The dependences on the number of links n are found for the following
properties of polymer fluid: the critical temperature T
c
, the critical pressure p
c
, the critical density p c, the critical compressibility z
c
, the temperature of normal boiling, the Riedel parameter of similarity a, the acentric factor Ω, and the enthalpy of vapor
formation δH V, A comparison with the experimental data for n-alkanes and 1-alkanols reveals that the obtained dependences reflect qualitatively correctly the variation of the above-identified
properties with an increase of the number of links in a molecule. For long chains (n ≪ 1), the scaling dependences are determined for the properties of a chain-molecule fluid: T
c
∽ n
−1/2, p
c
∽ n
−3/2ρ c∽ n
−1/2, z
c∽ n
−1,α∽ n, ω∽ n
2/3,Δ H
ν∽ n. 相似文献
19.
The glass transition temperature was studied via differential thermal analysis of glasses in the system (100 − x)TeO 2–5Bi 2O 3– xZnO and (100 − x)TeO 2–10Bi 2O 3– xZnO where x = 15, 20, 25 in mol%. The crystallization behavior and microstructure development of the 0.7TeO 2/0.1Bi 2O 3/0.2ZnO glass during annealing were investigated by non-isothermal differential thermal analysis (DTA), X-ray diffractometry,
and transmission electron microscopy. The glass transition temperature, crystallization temperature, and the nature of crystalline
phases formed were determined. From the heating rate dependence of the glass transition temperature, the glass transition
activation energy was derived. From variation of DTA peak maximum temperature with heating rate, the activation energies of
crystallization were calculated to be 305.8 and 197 kJ mol −1 for first and second crystallization exotherms, respectively. Moreover, synthesized crystalline Bi 3.2Te 0.8O 6.4, Bi 2Te 4O 11, and Zn 2Te 3O 8 were investigated. In addition, the change in particle size with increasing annealing time was observed by high-polarized
optical microscope. 相似文献
20.
As a positive temperature coefficient of resistivity (PTCR) material, Ba 0.92Ca 0.05(Bi 0.5Na 0.5) 0.03TiO 3 ceramics with donor doping of Nb 5+ and acceptor doping of Mn 2+ were prepared by a conventional mixed oxide method. The influence of contents of Nb 5+ and Mn 2+ on the microstructure and PTCR characteristics of Ba 0.92Ca 0.05(Bi 0.5Na 0.5) 0.03TiO 3 ceramics sintered at 1,360°C for 2 h was investigated. The result showed that the Curie temperature ( T
c) was shifted to a lower temperature with increasing of the content of Nb 5+ and the resistance jump (ρ max/ρ min) was enhanced with doping of Mn 2+. The grain size of ceramic sample decreased with increasing of contents of donor Nb 5+ and acceptor Mn 2+. The Ba 0.92Ca 0.05(Bi 0.5Na 0.5) 0.03TiO 3 ceramic with 0.4 mol%Nb 5+ and 0.04 mol%Mn 2+ exhibited a low ρ RT of 5.0 × 102 Ω cm, a typical PTCR effect of ρ max/ρ min > 10 3, and a T
c of 158°C. 相似文献
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