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1.
《Solid State Ionics》2006,177(19-25):1747-1752
Oxygen tracer diffusion coefficient (D⁎) and surface exchange coefficient (k⁎) have been measured for (La0.75Sr0.25)0.95Cr0.5Mn0.5O3−δ using isotopic exchange and depth profiling by secondary ion mass spectrometry technique as a function of temperature (700–1000 °C) in dry oxygen and in a water vapour-forming gas mixture. The typical values of D⁎ under oxidising and reducing conditions at ∼ 1000 °C are 4 × 10− 10 cm2 s− 1 and 3 × 10− 8 cm2 s− 1 respectively, whereas the values of k⁎ under oxidising and reducing conditions at ∼ 1000 °C are 5 × 10− 8 cm s− 1 and 4 × 10− 8 cm s− 1 respectively. The apparent activation energies for D⁎ in oxidising and reducing conditions are 0.8 eV and 1.9 eV respectively. 相似文献
2.
Borophene, an atomically thin, corrugated, crystalline two-dimensional boron sheet, has been recently synthesized. Here we investigate mechanical properties and lattice thermal conductivity of borophene using reactive molecular dynamics simulations. We performed uniaxial tensile strain simulations at room temperature along in-plane directions, and found 2D elastic moduli of 188 N m−1 and 403 N m−1 along zigzag and armchair directions, respectively. This anisotropy is attributed to the buckling of the borophene structure along the zigzag direction. We also performed non-equilibrium molecular dynamics to calculate the lattice thermal conductivity. Considering its size-dependence, we predict room-temperature lattice thermal conductivities of 75.9 ± 5.0 W m−1 K−1 and 147 ± 7.3 W m−1 K−1, respectively, and estimate effective phonon mean free paths of 16.7 ± 1.7 nm and 21.4 ± 1.0 nm for the zigzag and armchair directions. In this case, the anisotropy is attributed to differences in the density of states of low-frequency phonons, with lower group velocities and possibly shorten phonon lifetimes along the zigzag direction. We also observe that when borophene is strained along the armchair direction there is a significant increase in thermal conductivity along that direction. Meanwhile, when the sample is strained along the zigzag direction there is a much smaller increase in thermal conductivity along that direction. For a strain of 8% along the armchair direction the thermal conductivity increases by a factor of 3.5 (250%), whereas for the same amount of strain along the zigzag direction the increase is only by a factor of 1.2 (20%). Our predictions are in agreement with recent first principles results, at a fraction of the computational cost. The simulations shall serve as a guide for experiments concerning mechanical and thermal properties of borophene and related 2D materials. 相似文献
3.
《Physics letters. A》2020,384(25):126457
The flat hexagonal borophene oxide (B2O) has the highest Li storage capacity among existing two-dimensional materials. Thermal conductivity is an important parameter for the safety of Li-ion batteries. We investigate the lattice thermal conductivity of B2O by solving phonon Boltzmann transport equation combined with the first-principles calculations. We found that the relaxation time approximation remarkably underestimate the thermal conductivity (κ) of monolayer B2O, revealing phonon hydrodynamics characteristic. The κ of B2O from the exact solution of Boltzmann transport equation is 53 W m−1 K−1 and 130 W m−1 K−1 along armchair-direction and zigzag-direction at 300 K, respectively. B2O exhibits strong thermal transport anisotropy due to anisotropic phonon group velocity, obviously larger than that of other borophene allotropes. At room temperature, the phonon mean free path of B2O is about 231 nm and 49 nm along armchair-direction and zigzag-direction, respectively. The highly anisotropic thermal conductivity of B2O offers new possibilities for its applications in thermal management. 相似文献
4.
《Current Applied Physics》2009,9(2):359-366
The equilibrated grain boundary groove shapes for solid carbon tetrabromide (CTB) in equilibrium with its melt were directly observed by using a horizontal temperature gradient stage. From the observed grain boundary groove shapes, Gibbs–Thomson coefficient (Γ) and solid–liquid interfacial energy (σSL) and grain boundary energy (σgb) of CTB have been determined to be (7.88 ± 0.8) × 10−8 K m, (6.91 ± 1.04) × 10−3 J m−2 and (13.43 ± 2.28) × 10−3 J m−2, respectively. The ratio of thermal conductivity of equilibrated liquid phase to solid phase for CTB has also been measured to be 0.90 at its melting temperature. The value of σSL for CTB obtained in present work was compared with the values of σSL determined in the previous works for same material and it was seen that the present result is in good agreement with previous works. 相似文献
5.
Temperature dependence of the electrical conductivity of CuInS2–ZnIn2S4 and CuInSe2–ZnIn2Se4 solid solutions possessing n-type conductivity has been studied. It has been established that when the temperature decreases down to ~100 to 27 K, the hopping mechanism of electrical conductivity with a variable jumping length between localized states positioned in a narrow energy band near the Fermi level becomes dominant. The main parameters of the hopping conductivity have been determined. At higher temperatures (150–300 K), in the CuInSe2–ZnIn2Se4 single crystals containing 15 and 20 mol% ZnIn2Se4 the thermally activated conductivity with activation energy of 0.018 and 0.04 eV, respectively, is detected. Among the CuInSe2–ZnIn2Se4 single crystals, samples with 5 and 10 mol% ZnIn2Se4 were found to be close to degenerate semiconductors. Temperature dependences of the electrical conductivity of CuInS2–ZnIn2S4 single crystals are described by a more complicated function that may indicate a competition of several conduction mechanisms in these compounds. For the CuInS2–ZnIn2S4 solid solutions, X-ray photoelectron core-level and valence-band spectra have been measured for both pristine and Ar+ ion-bombarded surfaces. Our results indicate that the Cu1−xZnxInS2 single-crystal surfaces are sensitive to Ar+ ion-bombardment. Additionally, for the Cu1−xZnxInS2 crystal with the highest ZnIn2S4 content, namely 12 mol% ZnIn2S4, the X-ray emission bands representing the energy distribution of the Cu 3d, Zn 3d and S 3p states have been measured and compared on a common energy scale with the X-ray photoelectron valence-band spectrum. 相似文献
6.
A high-pressure optical zone-melting technique was employed to grow a Mn-rich Heusler Mn50Ni37Co3In10 unidirectional crystal in the present study. It was found that the Co-doped Mn50Ni37Co3In10 unidirectional crystal showed a low magnetic hysteretic loss and a widened working temperature interval in the vicinity of the martensitic transformation. The inverse magnetic entropy change (∆SM) reached 7.84 Jkg−1K−1 around 237.5 K under a magnetic field change of 30 kOe, and the corresponding effective refrigeration capacity (RCeff) was about 127.2 Jkg−1. The experimental results demonstrated a high potential to develop high-performance Mn-rich Heusler Mn–Ni–In magnetocaloric materials by means of Co doping in combination with the high-pressure optical zone-melting fabrication technique. 相似文献
7.
A simple method for synthesis of gold nanoparticles (AuNPs) using Aspergillum sp. WL-Au was presented in this study. According to UV–vis spectra and transmission electron microscopy images, the shape and size of AuNPs were affected by different parameters, including buffer solution, pH, biomass and HAuCl4 concentrations. Phosphate sodium buffer was more suitable for extracellular synthesis of AuNPs, and the optimal conditions for AuNPs synthesis were pH 7.0, biomass 100 mg/mL and HAuCl4 3 mM, leading to the production of spherical and pseudo-spherical nanoparticles. The biosynthesized AuNPs possessed excellent catalytic activities for the reduction of 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, o-nitroaniline and m-nitroaniline in the presence of NaBH4, and the catalytic rate constants were calculated to be 6.3×10−3 s−1, 5.5×10−3 s−1, 10.6×10−3 s−1, 8.4×10−3 s−1 and 13.8×10−3 s−1, respectively. The AuNPs were also able to catalyze the decolorization of various azo dyes (e.g. Cationic Red X-GRL, Acid Orange II and Acid scarlet GR) using NaBH4 as the reductant, and the decolorization rates reached 91.0–96.4% within 7 min. The present study should provide a potential candidate for green synthesis of AuNPs, which could serve as efficient catalysts for aromatic pollutants degradation. 相似文献
8.
To elucidate the thermoelectric properties at high temperatures, the electrical conductivity and Seebeck coefficient were measured at temperatures between 423 K and 973 K for perovskite-type ceramics of BaBi1?xSbxO3 solid solutions with x=0.0–0.5. All the ceramics exhibit p-type semiconducting behaviors and electrical conduction is attributed to hopping of small polaronic holes localized on the pentavalent cations. Substitution of Bi with Sb causes the electrical conductivity σ and cell volume to decrease, but the Seebeck coefficient S to increase, suggesting that the Sb atoms are doped as Sb5+ and replace Bi5+, reducing 6s holes conduction from Bi5+(6s0) to Bi3+ (6s2). The thermoelectric power factor S 2σ has values of 6×10?8–3×10?5 W m?1 K?2 in the measured temperature range, and is maximized for an Sb-undoped BaBiO3?δ, but decreases upon Sb doping due to the decreased σ values. 相似文献
9.
《Solid State Ionics》2006,177(33-34):2945-2950
Ni-based cermets were prepared and reduced from mixtures of NiO and Ba2In0.6Ti1.4O5.7□0.3. A cermet containing 18.7 vol.% of Ni exhibits promising characteristics: 40% of open porosity and a lower DC resistivity than a Ni/YSZ cermet with a larger Ni content (30 vol.%). Its thermal expansion coefficient is 11.4 × 10− 6 K− 1 whereas that measured for Ba2In0.6Ti1.4O5.7□0.3 is 9.9 × 10− 6 K− 1. Electrical measurements vs. the Ni content have shown that the percolation threshold corresponds to 15.7 vol.% of Ni. By using saccharose as a pore former, the porosity of the electrode can be tuned. It is shown that the pore size is controlled by the particle size distribution of the pore former. 相似文献
10.
(K0.5Na0.5)NbO3 (KNN)/[P(VDF-TrFE)70:30] composite thick films with different KNN weight ratios have been fabricated and the effect of KNN mass content on the material structure and properties have been studied in this paper. Properties of the infrared sensor based KNN/[P(VDF-TrFE)70:30] composite thick film were also systematically studied. It was found that the sample containing 30 wt.% KNN show optimal properties for pyroelectric appliance and the highest pyroelectric coefficient was 63 μCm−2 K−1. Infrared sensors using 30 wt.% KNN-70 wt.%[P(VDF-TrFE)70:30] show highest detectivity (D1 = 3.21 × 108 cm Hz1/2 W−1) at 137.3 Hz, indicating it is an promising candidate in lead-free quick response infrared detectors. 相似文献
11.
《Solid State Ionics》2009,180(40):1683-1689
The complex perovskite (Pr0.75Sr0.25)1 − xCr0.5Mn0.5O3 − δ (PSCM) has been prepared and studied as possible anode material for high-temperature solid oxide fuel cells (SOFCs). PSCM exhibits GdFeO3-type structure and is both physically and chemically compatible with the conventional YSZ electrolyte. The reduction of PSCM resulted in structural change from orthorhombic Pbnm to cubic Pm-3m. Selected area electron diffraction (SAED) analysis on the reduced phases indicated the presence of a √2 × √2 × 2 superlattice. The total conductivity values of ∼ 75% dense Pr0.75Sr0.25Cr0.5Mn0.5O3 − δ at 900 °C in air and 5% H2/Ar are 9.6 and 0.14 S cm− 1 respectively. The conductivity of PSCM drops with decreasing Po2 and is a p-type conductor at all studied Po2. The average TEC of Pr0.75Sr0.25Cr0.5Mn0.5O3 − δ is 9.3 × 10− 6 K− 1, in the temperature range of 100–900 °C and is close to that of YSZ electrolyte. The anode polarization resistance of PSCM in wet 5%H2 is 1.31 Ω cm2 at 910 °C and in wet CH4 at 930 °C; the polarization resistance is 1.29 Ω cm2. PSCM was unstable at 900 °C in unhumidified hydrogen. Cell performance measurements carried out using graded PSCM and La0.8Sr0.2MnO3 as anode and cathode respectively yielded a maximum power density of 0.18 W cm− 2 in wet 5%H2/Ar at 910 °C and the corresponding current density was 0.44 A cm− 2 at 0.4 V. The activation energy for the electrochemical cell operating in wet (3% H2O) 5%H2/Ar fuel is 85 kJ mol− 1. 相似文献
12.
《Current Applied Physics》2010,10(4):1071-1075
The physical and electrochemical properties of the activated carbon pellet electrodes have been investigated. Activated carbon pellets were prepared from single step carbonization process of pre-carbonized rubber wood sawdust at a temperature of 800 °C that followed with a CO2 activation process at temperature in the range of 700–1000 °C. The BET characterization on the sample found that the surface area of the carbon pellet increased with the increasing of the activation temperature. The optimum value was as high as 683.63 m2 g−1. The electrical conductivity was also found to increase linearly with the increasing of the activation temperature, namely from 0.0075 S cm−1 to 0.0687 S cm−1 for the activation temperature in the range of 700–1000 °C. The cyclic voltammetry characterization of the samples in aqueous solution of 1 M H2SO4 also found that the specific capacitance increased with the increasing of the activation temperature. Typical optimum value was shown by the sample activated at 900 °C with the specific capacitance was as high as 33.74 F g−1 (scan rate 1 mV s−1). The retained ratio was as high as 32.72%. The activated carbon pellet prepared from the rubber wood sawdust may found used in supercapacitor applications. 相似文献
13.
Porous lead zirconate titanate (PbZr0.3Ti0.7O3, PZT30/70) thick films and detectors for pyroelectric applications have been fabricated on alumina substrates by screen-printing technology. Low temperature sintering of PZT thick films have been achieved at 850 °C by using Li2CO3 and Bi2O3 sintering aids. The microstructure of PZT thick film has been investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The dielectric properties were measured using HP 4284 at 1 kHz under 25 °C. The permittivity and loss tangent of the thick films were 94 and 0.017, respectively. Curie temperature of PZT thick film was 425 °C as revealed by dielectric constant temperature measurement. The pyroelectric coefficient was determined to be 0.9 × 10−8 Ccm−2 K−1 by dynamic current measurement. Infrared detector sensitive element of dual capacitance was fabricated by laser directly write technology. Detectivity of the detectors were measured using mechanically chopped blackbody radiation. Detectivity ranging from 1.23 × 108 to 1.75 × 108 (cm Hz1/2 W−1) was derived at frequency range from 175.5 Hz to 1367 Hz, and D*’s −3 dB cut-off frequency bandwidth was 1.2 kHz. The results indicate that the infrared detectors based on porous thick films have great potential applications in fast and wide-band frequency response conditions. 相似文献
14.
Ning Lang Min-Ying Su Hon J. Yu Muqing Lin Mark J. Hamamura Huishu Yuan 《Magnetic resonance imaging》2013,31(8):1285-1291
Spinal myeloma and metastatic cancer cause similar symptoms and show similar imaging presentations, thus making them difficult to differentiate. In this study, dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was performed to differentiate between 9 myelomas and 22 metastatic cancers that present as focal lesions in the spine. The characteristic DCE parameters, including the peak signal enhancement percentage (SE%), the steepest wash-in SE% during the ascending phase and the wash-out SE%, were calculated by normalizing to the precontrast signal intensity. The two-compartmental pharmacokinetic model was used to obtain Ktrans and kep. All nine myelomas showed the wash-out DCE pattern. Of the 22 metastatic cancers, 12 showed wash-out, 7 showed plateau, and 3 showed persistent enhancing patterns. The fraction of cases that showed the wash-out pattern was significantly higher in the myeloma group than the metastatic cancer group (9/9 = 100% vs. 12/22 = 55%, P = .03). Compared to the metastatic cancer group, the myeloma group had a higher peak SE% (226% ± 72% vs. 165% ± 60%, P = .044), a higher steepest wash-in SE% (169% ± 51% vs. 111% ± 41%, P = .01), a higher Ktrans (0.114 ± 0.036 vs. 0.077 ± 0.028 1/min, P = .016) and a higher kep (0.88 ± 0.26 vs. 0.49 ± 0.23 1/min, P = .002). The receiver operating characteristic analysis to differentiate between these two groups showed that the area under the curve was 0.798 for Ktrans, 0.864 for kep and 0.919 for combined Ktrans and kep. These results show that DCE-MRI may provide additional information for making differential diagnosis to aid in choosing the optimal subsequent procedures or treatments for spinal lesions. 相似文献
15.
W. Ren K.-Y. Lam S.H. Pyun A. Farooq D.F. Davidson R.K. Hanson 《Proceedings of the Combustion Institute》2013,34(1):453-461
Reaction rate coefficients for the major high-temperature methyl formate (MF, CH3OCHO) decomposition pathways, MF → CH3OH + CO (1), MF → CH2O + CH2O (2), and MF → CH4 + CO2 (3), were directly measured in a shock tube using laser absorption of CO (4.6 μm), CH2O (306 nm) and CH4 (3.4 μm). Experimental conditions ranged from 1202 to 1607 K and 1.36 to 1.72 atm, with mixtures varying in initial fuel concentration from 0.1% to 3% MF diluted in argon. The decomposition rate coefficients were determined by monitoring the formation rate of each target species immediately behind the reflected shock waves and modeling the species time-histories with a detailed kinetic mechanism [12]. The three measured rate coefficients can be well-described using two-parameter Arrhenius expressions over the temperature range in the present study: k1 = 1.1 × 1013 exp(?29556/T, K) s?1, k2 = 2.6 × 1012 exp(?32052/T, K) s?1, and k3 = 4.4 × 1011 exp(?29 078/T, K) s?1, all thought to be near their high-pressure limits. Uncertainties in the k1, k2 and k3 measurements were estimated to be ±25%, ±35%, and ±40%, respectively. We believe that these are the first direct high-temperature rate measurements for MF decomposition and all are in excellent agreement with the Dooley et al. [12] mechanism. In addition, by also monitoring methanol (CH3OH) and MF concentration histories using a tunable CO2 gas laser operating at 9.67 and 9.23 μm, respectively, all the major oxygen-carrying molecules were quantitatively detected in the reaction system. An oxygen balance analysis during MF decomposition shows that the multi-wavelength laser absorption strategy used in this study was able to track more than 97% of the initial oxygen atoms in the fuel. 相似文献
16.
InP-based InGaAsP photodetectors targeting on 1.06 μm wavelength detection have been grown by gas source molecular beam epitaxy and demonstrated. For the detector with 200 μm mesa diameter, the dark current at 10 mV reverse bias and R0A are 8.89 pA (2.2 × 10−8 A/cm2) and 3.9 × 105 Ω cm2 at room temperature. The responsivity and detectivity of the InGaAsP detector are 0.30 A/W and 1.45 × 1012 cm Hz1/2 W−1 at 1.06 μm wavelength. Comparing to the reference In0.53Ga0.47As detector, the dark current of this InGaAsP detector is about 570 times lower and the detectivity is more than ten times higher, which agrees well with the theoretical estimation. 相似文献
17.
The dielectric and pyroelectric responses of MgO-modified Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 ceramics were investigated near FR(LT)–FR(HT) phase transition. It was found that MgO additive reduced the FR(LT)–FR(HT) phase transition temperature from 41 °C to room temperature (24 °C). Superior room-temperature pyroelectric properties were obtained in the composition of 0.10 wt% MgO addition without DC bias. The largest pyroelectric coefficient, 65 × 10−8 C cm−2 K−1, was detected. Accordingly, the detectivity figures of merit Fd had maximum values of 20 × 10−5 Pa−1/2, and especially the voltage responsivity Fv = 0.91 m2C−1 is the highest value reported so far among all pyroelectric materials. It shows promising potential for application in uncooled pyroelectric infrared detector. 相似文献
18.
The thermoelectric properties of Mo-substituted CrSi2 were studied. Dense polycrystalline samples of Mo-substituted hexagonal C40 phase Cr1−xMoxSi2 (x=0–0.30) were fabricated by arc melting followed by spark plasma sintering. Mo substitution substantially increases the carrier concentration. The lattice thermal conductivity of CrSi2 at room temperature was reduced from 9.0 to 4.5 W m−1 K−1 by Mo substitution due to enhanced phonon–impurity scattering. The thermoelectric figure of merit, ZT, increases with increasing Mo content because of the reduced lattice thermal conductivity. The maximum ZT value obtained in the present study was 0.23 at 800 K, which was observed for the sample with x=0.30. This value is significantly greater than that of undoped CrSi2 (ZT=0.13). 相似文献
19.
Robert S. Tranter Patrick T. Lynch Xueliang Yang 《Proceedings of the Combustion Institute》2013,34(1):591-598
The decomposition of dimethyl ether (CH3OCH3) has been investigated behind incident shock waves in a diaphragmless shock tube using laser schlieren densitometry, LS (T = 1500–2450 K, P = 57 ± 4, 125 ± 5 and 253 ± 12 Torr). The LS density gradient profiles were simulated and excellent agreement was found between the simulations and experimental profiles. Rate coefficients for CH3OCH3 → CH3O + CH3 were obtained. They showed strong fall-off, and at the lower end of the experimental temperature range are close to the low pressure limit. First order rate coefficient expressions were determined over 1500 < T < 2450 K. k57Torr = (3.10 ± 1.0) × 1079T?19.03 exp(?54417/T) s?1, k125Torr = (1.12 ± 0.3) × 1083T?19.94 exp(?55554/T) s?1and k253Torr = (1.02 ± 0.3) × 1073T?17.09 exp(?51500/T) s?1. The effect of a roaming channel for decomposition of dimethyl ether was assessed and the best agreement was obtained with 1% dissociation of DME via the roaming path. 相似文献
20.
《Solid State Ionics》2006,177(19-25):1849-1853
Single phase materials of the La(2−x)SrxMnO4±δ (0.6 ≤ x ≤ 2.0) solid solution series were prepared via solid state reaction. The structure of each material was examined at room temperature and determined to be tetragonal for all phases examined. An expansion in lattice volume was observed on increasing lanthanum content. The stability and thermal expansion of each member of the solid solution series was determined via the use of in situ high temperature X-ray diffraction. It was found that all materials remained stable up to a temperature of 800 °C. Thermal expansion coefficients were found to be in the region of 15 × 10− 6 K− 1 for La(2−x)SrxMnO4±δ compounds where x > 1.4. The electrical conductivity of each phase was also determined over a similar temperature range with a maximum value of ∼6 Scm− 1 at 900 °C for the x = 1.8 phase. 相似文献