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1.
From light-scattering studies on polybutylmethacrylate, a polymeric glass, the variation of the velocity and attenuation of thermally excited hypersonic phonons with temperature has been measured. Measurement of the temperature dependence of the ratio of the intensity of the Rayleigh line to the Brillouin lines is interpreted as due to a configurational rearrangement within the glass above the glass transition temperature, Tg . Only light scattered from longitudinal phonons was observed. The distinct change in the temperature dependence of the velocity, attenuation and intensity ratio identified the glass transition. For samples annealed well above Tg, Tg was found to be about 0°C from the light-scattering studies, 12°C from differential scanning calorimetry (DSC), and 20°C from refractive index measurements. For an unannealed sample the behaviour of the above parameters with temperature was found to be different. Tg for the unannealed sample was 14°C from light-scattering, 18°C from DSC and 20°C from index of refraction measurements. 相似文献
2.
The crystallization and glass transition kinetics using differential scanning calorimetry (DSC) in 50AgI–33.33Ag2O–16.67[(V2O5)1−x
–(MoO3)
x
] superionic glassy system is discussed. Thermal stability of glass, studied using various criteria, does not vary significantly
with glass former variation. However, the activation energies for structural relaxation (E
s) at glass transition temperature and crystallization (E
c) obtained using Moynihan and Kissinger, Matusita-Sakka formulations found to exhibit interesting trends with MoO3 substitution in the glass matrix. It is noticed that the electrical conductivity (σ)–temperature (T) cycles obtained at a typical heating rate of 1 °C/min do exhibit significant thermal events. The conductivity after first
heating cycle at room temperature is found to be increasing with MoO3 content and maximum for x = 0.3 (~10−3 Ω−1 cm−1 at 30 °C) which is comparable to that of the host 50AgI–33.33Ag2O–16.67V2O5 glassy system. The parameters obtained from σ–T plots and DSC scans do complement each other in a particular range of composition. 相似文献
3.
J. C. Cruz V. Baglio S. Siracusano R. Ornelas L. Ortiz-Frade L. G. Arriaga V. Antonucci A. S. Aricò 《Journal of nanoparticle research》2011,13(4):1639-1646
Nanosized IrO2 electrocatalysts (d ~ 7–9 nm) with specific surface area up to 100 m2 g−1 were synthesized and characterized for the oxygen evolution reaction in a solid polymer electrolyte (SPE) electrolyzer. The
catalysts were prepared by a colloidal method in aqueous solution and a subsequent thermal treatment. An iridium hydroxide
hydrate precursor was obtained at ~100 °C, which was, successively, calcined at different temperatures from 200 to 500 °C.
The physico-chemical characterization was carried out by X-ray diffraction (XRD), thermogravimetry–differential scanning calorimetry
(TG–DSC) and transmission electron microscopy (TEM). IrO2 catalysts were sprayed onto a Nafion 115 membrane up to a loading of 3 mg cm−2. A Pt catalyst was used at the cathode compartment with a loading of 0.6 mg cm−2. The electrochemical activity for water electrolysis of the membrane-electrode assemblies (MEAs) was investigated in a single
cell SPE electrolyzer by steady-state polarization curves, impedance spectroscopy and chrono-amperometric measurements. A
maximum current density of 1.3 A cm−2 was obtained at 1.8 V and 80 °C for the IrO2 catalyst calcined at 400 °C for 1 h. A stable performance was recorded in single cell for this anode catalyst at 80 °C. The
suitable catalytic activity and stability of the most performing catalyst were interpreted in terms of proper combination
between nanostructure and suitable morphology. 相似文献
4.
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
5.
R. Rai 《Zeitschrift für Physik B Condensed Matter》1995,99(1):327-332
The closeness of low-lying T1u and T1g levels of C
60
−
could enable their mixing under an odd parity vibration of (T1 u + T1 g ⊗ (hg + τ1 u)type. In addition, the two levels are susceptible to Jahn-Teller interaction due to five-fold degenerate hg vibrations. This complex problem of (T1u+T1g)⊗(hg+τ1u) vibronic interaction is transformed to a form similar to T2g ⊗ (εg + τ2g) vibronic problem of octahedral symmetry. The problem is analysed in an infinite coupling model and compared with the experimental
spectroscopic results for the C
60
−
radical. The resulting parameters are used to calculate the pair-binding energy and superconducting transition temperature
in C
60
n−
fullerides. Vibronic mixing with the T1g level is found to be responsible for maximising the pair-binding energy at the doping level n=3. It is also found to be an
important source of Tc enhancement. 相似文献
6.
S. V. Demishev A. V. Semeno N. E. Sluchanko N. A. Samarin J. Singleton A. Ardavan S. J. Blundell W. Hayes S. Kunii 《JETP Letters》1996,64(10):760-766
In undoped pure single crystals of the mixed valence compound SmB6 anomalous ESR absorption is observed in the frequency range v=40–120 GHz at temperatures of 1.8–4.2 K. The ESR for the case of the coherent ground state consists of two components corresponding
to g-factors g
1=1.907±0.003 and g
2=1.890±0.003. The amplitude of both ESR lines strongly depends on temperature in the temperature range studied: the amplitude
of the first line with g=g
1 increases and the amplitude of the second line decreases with temperature. A model based on consideration of intrinsic defects
in the SmB6 crystalline lattice, with a densit ∼1015−1016 cm−3, is suggested as an explanation for the anomalous ESR-behavior. In the frequency range v>70 GHz at T=4.2 K, in addition to the main ESR lines, a new magnetic resonance with a hysteretic field dependence is discovered.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 10, 707–712 (25 November 1996)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
7.
V. Singh S. Watanabe T. K. Gundu Rao I.-J. Lee 《Applied physics. B, Lasers and optics》2011,104(4):1019-1027
Tricalcium aluminate doped with Eu3+ was prepared at furnace temperatures as low as 500°C by using the convenient combustion route and examined using powder X-ray
diffraction, scanning electron microscope and photoluminescence techniques. A room-temperature photoluminescence study showed
that the phosphors can be efficiently excited by UV/Visible region, emitting a red light with a peak wavelength of 616 nm
corresponding to the 5D0–7F2 transition of Eu3+ ions. The phosphor exhibits three thermoluminescence (TL) peaks at 195°C, 325°C and 390°C. Electron Spin Resonance (ESR)
studies were carried out to study the defect centres induced in the phosphor by gamma irradiation and also to identify the
defect centres responsible for the TL process. Room-temperature ESR spectrum of irradiated phosphor appears to be a superposition
of three distinct centres. One of the centres (centre I) with principal g-value 2.0130 is identified as O− ion while centre II with an axially symmetric principal values g
∥=2.0030 and g
⊥=2.0072 is assigned to an F+ centre (singly ionized oxygen vacancy). O− ion (hole centre) correlates with the TL peak at 195°C and the F+ centre (electron centre), which acts as a recombination centre, is also correlated to the 195°C TL peak. F+ centre further appears to be related to the high temperature peak at 390°C. Centre III is also assigned to an F+ centre and seems to be the recombination centre for the TL peak at 325°C. 相似文献
8.
Electron spin resonance (ESR) study was done on calcite encrustation on Fili neotectonic fault surface, Greece. Normally such
calcite encrustations on fault surfaces are not observed. Significantly, the ESR study has detected the presence of nitrate
NO32− radical in this calcite encrustation, havingg
⊥=2.0063±0.0001 and hyperfine coupling constantA
⊥=3.44 mT, the second such detection of nitrate NO32− radical following a sample from Scott Glacier, Antarctica. From isochronal thermal annealing measurement the NO32− radical was found to be quite stable, only fully annealed at 475°C. This study also shows that the ESR, as a tool, can be
suitably applied to date the age of formation of the calcite encrustation with SO3− as an ESR dating signal by additive γ-ray irradiation. A preliminary estimation indicates the age of formation of calcite
precipitation at Fili fault, Greece to be about 5600 years. 相似文献
9.
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
10.
Lisa Richards Denny Raymond F. Boyer Hans-Georg Ellas 《Journal of Macromolecular Science: Physics》2013,52(3):227-265
A differential scanning calorimeter (DSC) investigation (heating rate 10 K/min) is presented on the multiple transition (relaxation) spectra of PMMA: Tβ < Tg; Tg, Tll > Tg; and Tlρ > Tll, as a function of tacticity. Specimens are characterized by fractional triad content: isotactic (it-), Xii; syndiotactic (st-), Xss; and atactic (at-), Xis. Values for the seven specimens are it-, 1.0;, at-, 0.495 to 0.750; st-, 0.958. Results on Tβ were inconclusive. Our Tg results clarify some discrepancies in the prior literature. Linear least squares regression analyses give: Tg (°C) = 56.6 + 76.6 Xss (our data) Tg (°C) = 49.1 + 87.3 Xss (our data plus selected literature data) Extrapolated Tg 's for Xss = 1 are 133.2°C and 136.1°C, respectively, in contrast to Thompson's extrapolated value of 160°C. Similarly Tg(°C) = 99.5 + 71.6 (1?Xii) for our DSC data. The extrapolated Tll for Xss = 1 is 171.1°C. The intensity of Tll is high for st-and it-, with a broad minimum over the at-region. A second liquid state process, Tlρ > Tll, occurs at 149°C for it-, but is above the measured range for at-and st-. Tll (at-) from DSC compares favorably with reported literature values by a variety of techniques. Tll and Tlρ at all tacticities agree well with those from a companion study by the thermally stimulated current (TSC) technique on the same group of specimens, as reported elsewhere. This includes the influence of tacticity on intensity. These cross-comparisons by a variety of methods indicate that neither Tll nor Tlρ is an artifact of our DSC technique. The Frenkel segment-segment contact hypothesis is favored to explain the molecular origin of Tll Sequences longer than triads may be needed for improved correlations of Tg and Tlρ with tacticity. 相似文献
11.
45% semi-crystalline parylene-C (–H2C–C6H3Cl–CH2–)
n
thin films (5.8 μm) polymers have been investigated by broadband dielectric spectroscopy for temperatures above the glass
transition (T
g
=90°C). Good insulating properties of parylene-C were obtained until operating temperatures as high as 200°C. Thus, low-frequency
conductivities from 10−15 to 10−12 S/cm were obtained for temperatures varying from 90 to 185°C, respectively. This conductivity is at the origin of a significant
increase in the dielectric constant at low frequency and at high temperature. As a consequence, Maxwell–Wagner–Sillars (MWS)
polarization at the amorphous/crystalline interfaces is put in evidence with activation energy of 1.5 eV. Coupled TGA (Thermogravimetric
analysis) and DTA (differential thermal analysis) revealed that the material is stable up to 400°C. This is particularly interesting
to integrate this material for new applications as organic field effect transistors (OFETs). Electric conductivity measured
at temperatures up to 200°C obeys to the well-known Jonscher law. The plateau observed in the low frequency part of this conductivity
is temperature-dependent and follows Arrhenius behavior with activation energy of 0.97 eV (deep traps). 相似文献
12.
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
13.
In the present study, a kind of solid polymer electrolyte (SPE) based on poly(vinylidene difluoride-co-hexafluoropropylene)/poly(methyl methacrylate) blends was prepared by a casting method to solve the safety problem of lithium
secondary batteries. Owing to being plasticized with a room temperature ionic liquid, N-butyl-N′-methyl-imidiazolium hexafluorophosphate, the obtained SPE shows a thermal decomposition temperature over 300°C and an ionic
conductivity close to 10−3 S cm−1. The SPE-3 sample, in which the weight of two polymers is equivalent, possesses an ionic conductivity of 0.45 × 10−3 S cm−1 at 25°C and presents an electrochemical window of 4.43 V. The ionic conductivity of the SPE-3 is as high as 1.73 × 10−3 S cm−1 at 75°C approaching to that of liquid electrolyte. The electrochemical performances of the Li/LiFePO4 cells confirmed its feasibility in lithium secondary batteries. 相似文献
14.
The glass transition in Ge
x
Se1−x
) (0·1 ⩽x ⩽ 0·25) glasses has been investigated using the photoacoustic (PA) technique. It is found that the PA amplitude and phase
undergo anomalous changes at the glass transition temperatureT
g. The amplitude has critical minimum and phase has maximum values atT
g. The variation of the thermal diffusivity, determined by measuring the frequency dependence of the PA amplitude and phase,
with temperature shows sharp decrease near the glass transition temperature. The temperature dependence of the optical energy
gap also has been measured and it shows a decrease with temperature for all compositions, the rate of decrease being higher
for temperatures greater thanT
g. 相似文献
15.
Summary We study the reorientation process of a paramagnetic radical dissolved in supercooledo-terphenyl around and belowT
g via the Electron Spin Resonance spectroscopy. The experimental results are at variance with the hypothesis of diffusive reorientation
of the radical. Instead, the ESR lineshapes are fairly well reproduced by assuming that the radical reorientates via large
angular jumps with a width Δϕ=80°
−5°
+10°
. The results are compared with previous2H NMR studies.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994. 相似文献
16.
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
17.
Non-aqueous polymer gel electrolytes containing trifluoromethanesulfonic acid (HCF3SO3) and polyethylene oxide (PEO) as the gelling polymer has been studied. The increase in conductivity observed with the addition
of PEO to liquid electrolytes has been explained to be due to the breaking of ion aggregates present in electrolytes at higher
acid concentrations. The increase in free H+ ion concentration upon breaking of ion aggregates has also been observed in pH measurements and viscosity of gel electrolytes
has been found to increase with PEO addition. Polymer gel electrolytes containing dimethylacetamide (DMA) have σ ∼ 10−2 S/cm at room temperature and are stable over −50 to 125 °C range of temperature. Gels based on propylene carbonate (PC) and
ethylene carbonate (EC) are stable in the −50 to 40 °C temperature range and loose their gelling nature above 40 °C. 相似文献
18.
Non-aqueous polymer gel electrolytes containing trifluoromethanesulfonic acid (HCF3SO3) and polyethylene oxide (PEO) as the gelling polymer has been studied. The increase in conductivity observed with the addition
of PEO to liquid electrolytes has been explained to be due to the breaking of ion aggregates present in electrolytes at higher
acid concentrations. The increase in free H+ ion concentration upon breaking of ion aggregates has also been observed in pH measurements and viscosity of gel electrolytes
has been found to increase with PEO addition. Polymer gel electrolytes containing dimethylacetamide (DMA) have σ ∼ 10−2 S/cm at room temperature and are stable over −50 to 125 °C range of temperature. Gels based on propylene carbonate (PC) and
ethylene carbonate (EC) are stable in the −50 to 40 °C temperature range and loose their gelling nature above 40 °C. 相似文献
19.
V. Singh S. Watanabe T. K. Gundu Rao J. F. D. Chubaci I. Ledoux-Rak H.-Y. Kwak 《Applied physics. B, Lasers and optics》2010,98(1):165-172
Er and Yb co-doped ZnAl2O4 phosphors were prepared by solution combustion synthesis and the identification of Er and Yb were done by energy-dispersive
X-ray analysis (EDX) studies. A luminescence at 1.5 μm, due to the 4I13/2 →4I15/2 transition, has been studied in the NIR region in Er and Yb co-doped ZnAl2O4 phosphors upon 980 nm CW pumping. Er-doped ZnAl2O4 exhibits two thermally stimulated luminescence (TSL) peaks around 174°C and 483°C, while Yb co-doped ZnAl2O4 exhibits TSL peaks around 170°C and 423°C. Electron spin resonance (ESR) studies were carried out to identify defect centres
responsible for TSL peaks observed in the phosphors. Room temperature ESR spectrum appears to be a superposition of two distinct
centres. These centres are assigned to an O− ion and F+ centre. O− ion appears to correlate with the 174°C TSL peak and F+ centre appears to relate with the high temperature TSL peak at 483°C in ZnAl2O4:Er phosphor. 相似文献
20.
Xiangming He Weihua Pu Jianguo Ren Li Wang Jiulin Wang Changyin Jiang Chunrong Wan 《Ionics》2008,14(4):335-337
The charge/discharge characteristics of the sulfur composite cathodes were investigated at different temperatures and different
current densities. The composite presented the discharge capacities of 854 and 632 mAh g−1 at 60 and −20 °C, respectively, while it had the discharge capacities of 792 mAh g−1 at 25 °C. The composite presented the discharge capacities of 792 and 604 mAh g−1 at 55.6 and 667 mA g−1, respectively, at room temperature. The results showed that the sulfur composite cathodes presented good charge/discharge
characteristics between 60 and −20 °C and at a high c-rate up to 667 mA g−1. 相似文献