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1.
The dielectric properties of a 2.5 mol% Bi 2O 3 doped Ba-ferrite (BaFe 12O 19) have been investigated. The specimen shows a drastically enhanced (≈ 10 5 times) permittivity (ε) through local polarization of Fe 3+ electronic charges activated with nearby Bi 3+ sites. The ε value also depends reasonably on thermal annealing (causes grain growth) of the samples. The specimens comprising large particle sizes (1–20 μ m) usually exhibit smaller ε values and low dielectric losses. 相似文献
2.
Transport properties of SrCe 0.95Y 0.05O 3−δ were studied by impedance spectroscopy and by measuring open-cell voltage (OCV) and gas permeation. Ionic transference numbers were determined by measuring the OCV of concentration cells and water vapor evolution of an O 2/H 2 fuel cell. We observed interfacial polarization on the basis of the I– V curves obtained by discharging a hydrogen concentration cell or an O 2/H 2 fuel cell. The observed high protonic conductivity (high proton and low oxide ion transference numbers) makes SrCe 0.95Y 0.05O 3−δ a potential material for hydrogen separation. From proton conductivity measurements, under a given hydrogen partial pressure difference of 4%/0.488%, the hydrogen permeation rate (of a dense membrane with 0.11 cm in thickness) was calculated to be ≈0.072 cm 3 (STP) cm −2 min −1 at 800°C, whereas the permeation rate calculated from short-circuit current measurements was ≈0.023 cm 3 (STP) cm −2 min −1 at 800°C. The difference between calculated and observed permeation rates is probably due to interfacial polarization. 相似文献
3.
Ion-implantation-induced structural modifications in Y 1Ba 2Cu 3O 7−δ superconductor are examined by a grazing angle X- ray diffraction technique. By employing a range of grazing angles from 0.3° to 10° it is shown that 100 KeV Ar + inplantation of the superconductor leads to amorphization as well as modification of grain size and orientation at dose values lower than 10 16 ions/ cm 2. At the dose of 5 × 10 16 ions/ cm 2 the X-ray diffraction intensity is a factor of 6 less as compared to the original pellet, though the lines themselves are sharp. This shows coexistence of perovskite grains and amorphous matrix. 相似文献
4.
Experimental results are reported for the Hanle effect on the 3 2S 1/2 ↔ 3 2P 1/2 transition of sodium at vapour densities between 10 9 and 10 12 at/cm 3. 相似文献
5.
The data on the resistance and magnetoresistance (MR) as well as measurements of the linear and nonlinear susceptibilities are presented for a Nd 0.75Ba 0.25MnO 3 single crystal with the Curie temperature TC≈129 K. Although this compound remains insulating in the ferromagnetic state, its resistance has an anomaly near TC and it reveals the colossal magnetoresistance. The data on the magnetic response are well described by the dynamic scaling theory for 3D isotropic ferromagnets in the paramagnetic critical region at τ>τ *≈0.11, τ=( T− TC)/ TC. Below τ * an anomalous critical behavior is found that suggests the coexistence of two magnetic phases. This behavior is discussed in terms of a phase separation which can occur in the moderately doped manganites exhibiting an orbital ordering. 相似文献
6.
本文引入与浓度和厚度有关的k NL待定参数, 在J-O理论基础上, 对Er 3+/Yb 3+掺杂的LiNbO 3和LiTaO 3单晶衬底上 的多晶水热外延样品进行了基于吸收光谱的拟合计算. LiNbO 3:Ω 2=2.34× 10 -20 cm 2, Ω 4=0.77× 10 -20 cm 2, Ω 6=0.31×10 -20 cm 2, k NL=4.32× 10 -2 mol·m -2. LiTaO 3:Ω 2=1.68×10 -20 cm 2, Ω 4=0.84×10 -20 cm 2, Ω 6=0.45×10 -20 cm 2, k NL=9.17×10 -3 mol· m -2. 该方法可尝试推广到粉体或胶体等难以直接获得浓度和厚度数据的体系. 经上转换发光测试及光谱参数计分析认为Er 3+/Yb 3+离子的掺杂浓度比为1:1的情况下, 样品呈现绿色上转换发光光谱; 可尝试以降低基质声子能量的方法提高 4I 13/2能级 对 2H 11/2和 4S 3/2能级的量子剪裁效率. 相似文献
7.
K-band electron spin resonance (ESR) at 4.3 K has revealed the dipole-dipole (DD) interaction effects between [1 1 1]P b centers ( *Si ≡ Si 3 defects with unpaired sp 3 hybrid [1 1 1]) at the 2 dimensional (1 1 1)Si/SiO 2 interface. This has been enabled by the perfectly reversible H 2 passivation of P b, which affects the defect's spin state. Sequential hydrogenation at 253–353°C and degassing treatments in high vacuum at 743–835°C allowed to vary the P b density in the range 5 × 10 10 < [P b] (1.14 ± 0.06) × 10 13 cm -2. With increasing [P b] fine structure doublets are clearly resolved. It is found that (1 1 1)Si/SiO 2 interfaces, dry thermally grown at ≈920°C, naturally comprise a *Si ≡ Si 3 defect density — passivated or not — of 1.14 × 10 13 cm -2. 相似文献
8.
YBa 2Cu 3O 7−δ (YBCO) films with high critical current density ( Jc) were successfully fabricated on nickel tapes buffered with epitaxial NiO. NiO was prepared on the textured nickel tape by the surface-oxidation epitaxy (SOE) method. We have reported so far a critical temperature ( Tc) of 87 K and Jc=4–6×10 4 A/cm 2 (77 K, 0 T) for the YBCO films on NiO/Ni tapes. To enhance the superconducting properties of the YBCO films on the SOE-grown NiO, depositions of thin oxide cap layers such as YSZ, CeO 2, and MgO on NiO were investigated. These oxide cap layers were epitaxially grown on NiO and provided the template for the epitaxial growth of YBCO films. Substantially improved data of Tc=88 K and Jc=3×10 5 A/cm 2 (77 K, 0 T) and 1×10 4 A/cm 2 (77 K, Hc, 4 T) were obtained for YBCO film on NiO, by using a MgO cap layer with a thickness of 50 nm. The method described in this paper is a simple way to produce long YBCO tape conductors with high- Jc values. 相似文献
9.
The temperature dependence of the extended X-ray absorption fine structure (EXAFS) is studied in the high Tc superconductors, YBa 2Cu 3O 7−δ. The measurements were done at the Cu K-edge for samples of two orthorhombic phases ( Tc≈90 K and ≈58 K, respectively) and a nonsuperconducting tetragonal phase. Interatomic distances and mean square relative displacements σ 2 for Cu-O bonds are determined by the least squares refinement. The results indicate that values of σ 2 increase near Tc for both the orthorhombic samples. It is concluded that this anomalous behavior related to Tc is caused by an anomalous vibration of oxygen atoms in the Ba-O layer. Changes in the Cu-O distances from 300 to 20 K are not found. 相似文献
11.
The radioluminescence (RL) of carbon doped aluminium oxide (Al 2O 3:C) TL dosimeter material (TLD-500) was investigated using a 137Cs conversion electron source (which also emits β and γ) for simultaneous irradiation and luminescence excitation. Furthermore, RL dosimetry characteristics of this material were studied. The main RL emission occurs at 420 nm. That matches the known main TL and OSL emissions for this material as well as an emission that was investigated in earlier RL studies, excited at higher energies (4 MeV electrons) and very high pulse delivered doses (≈800 kGy·s −1). Furthermore, the saturation dose for the main peak is reached at the dose level of ≈80 Gy as known from TL and earlier RL investigations. Other peaks at 700 and 790 nm and broad emission bands at photon energies higher than 3.00 eV and others between 2.00 and 2.50 eV were observed. The 700 nm emission shows growth also at higher dose levels, and saturates at an estimated dose of ≈800 Gy. The 790 nm emission reaches its maximum intensity at ≈10 Gy absorbed dose. The reported results give an outlook to the usability and the potential of Al 2O 3:C combined with RL measurements for radiation dosimetry as well as for beta source calibration, using radioluminescence. 相似文献
12.
采用EuF 3薄层修饰低功函数金属Ag源、漏电极,制备了CuPc有机场效应晶体管,研究了不同厚度EuF 3对器件性能的影响。结果表明,EuF 3的厚度由0 nm增至0.6 nm时,接触电阻由23.65×10 5 Ω·cm减 至3.86×10 5 Ω·cm,使得器件载流子迁移率由1.5×10 -3 cm 2·V -1·s -1提高到4.65×10 -3 cm 2·V -1·s -1。 UPS测试结果表明,薄层EuF 3在Ag与有机半导体间形成了界面偶极势垒,使源漏电极表面功函数增大,空穴注入势垒降低,Ag电极与有机半导体层界面的接触电阻减小,进而提升了空穴的注入效率。 相似文献
13.
Cross sections for absorption from excited vibrational levels of the ground X3Σ -g state of molecular oxygen to the repulsive 1 3Π u state are given. The potential energy curve for the 1 3Π u state of O 2 is constructed to be consistent with predissociation data for the B3Σ -u state and with recent ab initio calculations. In the photon wavelength range of 200–320 nm the cross sections are smoothly oscillatory and in no case larger than 1 × 10 -21 cm 2. In the region of the Schumann-Runge bands the cross sections are of order 0.4 × 10 -21 cm 2. 相似文献
14.
Transient photoconductivity (σ ph) experiments have been carried out in single crystals of insulating La 2CuO 4+δ near the metal-insulator transition (δ≈ 1–2%). The time evolution of the σ ph changes dramatically with light intensity ( IL). At low IL, σ ph is characterized by power law time decay, t−, in the nanosecond time regime, and the exponent, , decreases significantly with increasing IL. As IL increases to 5 × 10 15 photons/cm 2, σ ph reaches 15 S/cm, and the lifetime of the conducting state is enhanced by more than two orders of magnitude: σ ph exhibits a delayed peak centered at approximately 30 ns. followed by exponential decay with time constant of 360 ns. The data reveal a continuous distribution of localized electronic states above the (hole) mobility edge; the M-I transition is achieved when the Fermi level is shifted away from the localized states and across the mobility edge either by chemical dopiing or by photo-excitation. The time of σ ph at high IL implies the formation of metastable metallic droplets after photo-excitation. 相似文献
15.
In this work, we compare positon capture and photo-beta disintegration probabilities in several stellar conditions. We show that the second process can be neglected with regard to the first one in strongly endothermic nuclear transitions, whereas photo-beta disintegration can be competitive with positon capture and even can have a greater likelihood than the latter process in weakly endothermic and exothermic transitions. In the range of temperature we consider here (T ≈ 109 °K), it appears that the lifetime ratio τ(ph)/τ(ec+) against photo-beta disintegration and positon capture is the smallest for densities in the neighbourhood of 106 g/cm3. Thus, we arrive at the conclusion that the photo-beta process can play a role in the synthesis of two “p” elements at least, 62144Sm and 80196Hg, for which the ratios τ(ph)/τ(ec+) are close to 10 and 20, respectively, in the most favourable stellar conditions. 相似文献
16.
研究了Yb 3+/Er 3+共掺60P 2O 5-15BaO-10Al 2O 3-5ZnO-10R 2O(R=Na,K)以P 2O 5为主体的磷基有源光纤材料的光谱性质,以及不同Yb 3+/Er 3+掺杂浓度对光谱性质的影响规律。当Er 3+浓度为9.100×10 19/cm 3、Yb 3+的掺杂浓度为5.407×10 20/cm 3、Yb 3+/Er 3+浓度比为6:1时,玻璃样品在1 531 nm处的受激发射截面最大,为6.17×10 -21 cm 2。同时,其荧光寿命为9.73 ms,荧光半高宽为53.16 nm,发射截面与半高宽的乘积为3.28×10 -32 m 3,综合性能最佳。 相似文献
17.
Data were taken at the energy 2 E = 990 MeV to search for multibody events, with the same large solid angle detector which has been used for the measurement of the , ω andφ production by e +e − annilations. Assuming a π +π −π 0π 0 production by the quasi two-body process e +e − → → ωπ 0 we give the correspondi ng cross section σ(e +e − → π +π −π 0π 0) = (1.1 ± 0.5) 10 −32 cm 2. Since no events with 3 and 4 charged pions have been observed σ(e +e − → π +π −π 0π −) 1.5 × 10 −33 cm 2. 相似文献
18.
ZnO:Ag films have been fabricated on a n-Si (1 1 1) substrate and then annealed in situ in an O 2 ambient, using Ag 2O as a silver dopant by pulsed laser deposition. Hall measurements reveal that the films prepared at 400 and 450 °C show p-type behavior with a hole concentration of 6.3×10 16–1.2×10 17 cm –3 and a mobility of 2.48–3.30 cm 2/V s. By combining Hall measurements, electron paramagnetic resonance (EPR) signals, and photoluminescence (PL) spectra, a correlation is observed between the free hole carriers, the Ag 2+ centers, and the neutral acceptor bound excitons. Additionally, the p-ZnO:Ag/n-Si heterojunction shows a diode-like I–V characteristic. 相似文献
19.
Quasi-elastic light scattering from individual electron single-particle excitations is observed experimentally and studied theoretically in n-GaAs and n-InP samples with nonparabolic dispersion of energy bands for a wide range of free-electron concentrations varying from ≈10 8 to ≈10 19 cm -3. The results indicate that the scattering mechanisms associated with charge-, spin- and momentum-density fluctuations are represented by different light scattering line shapes and occur in different concentration ranges. 相似文献
20.
We report for the first time the spectroscopy and the laser operation of GdAl 3(BO 3) 4: Nd 3+ (NGAB) near 1338 nm corresponding to the 4F 3/2→ 4I 13/2 channel. Their features have been found favorable for self-frequency doubling in order to generate a red radiation at 669 nm and more generally for self-frequency conversions. The emission cross-section in σ-polarization was estimated to be 5.5×10 −20 cm 2. We demonstrated self-frequency doubling despite of non-optimal experimental conditions. 相似文献
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