炭黑填充聚甲基乙烯基硅氧烷硫化胶的阻温特性与电阻弛豫

研究了炭黑填充硅橡胶硫化胶的热循环以及热处理过程中的导电行为,发现在热循环中阻温关系曲线逐渐向低电阻方向移动,而在恒温下发生电阻弛豫现象;分析了硫化胶的导电机制,讨论了阻温关系发生移动的原因.     

Magnetic properties of off-stoichiometric R2Co3Zn14 (R=Y,Gd) single crystals

Single crystal X-ray diffraction data indicate that the R₂Co₃Zn₁₄ (R=Gd, Y) phase crystallizes non-stoichiometrically with a mixed occupancy of Co/Zn atoms on the 12-coordinated transition metal site and one of the three zinc sites. The crystals are rhombohedral with R-3m space group. Magnetization measurements provide no evidence of localized 3d electron moment in Y₂Co_2.3Zn_14.7 which is non-magnetic down to 1.8 K. Thermodynamic and transport measurements on two Gd₂Co_3+xZn_14−x crystals reveal that the extra cobalt influences temperature below which the samples enter into an antiferromagnetic state: T_N=31.5(3) K for Gd₂Co₃Zn₁₄ and 28(1) K for Gd₂Co_4.2Zn_12.8. A lower magnetic ordering temperature of T_mag=6.0(2) K is common in both Gd samples.     

Effect of energetic electron beam treatment on Ga-doped ZnO thin films

Transparent conductive zinc oxide (ZnO) thin films were synthesized by a sol–gel spin coating method with the addition of Ga(NO₃)₃ in a Zn(CH₃COO)₂ solution and exposed to electron beam treatment. The UV–Vis spectra demonstrated that all of the films had transmittances of over 85% in the visible region. When Ga(NO₃)₃ was added to the ZnO precursor solution, the resistivity of the ZnO thin film decreased and the carrier concentration increased significantly. After electron beam treatment was performed on the 0.4 at.% Ga-doped ZnO film, the optical band gap increased and the resistivity significantly decreased resulting from the increases of the carrier concentration and mobility. By combining Ga doping and electron beam treatment, the resistivity of the ZnO thin film was reduced by a factor of nine hundred.     

Resistivity of thin gold films on mica induced by electron-surface scattering: Application of quantitative scanning tunneling microscopy

We report a comparison between the resistivity measured on thin gold films deposited on mica, with predictions based upon classical theories of size effects (Drude's, Sondheimer's and Calecki's), as well as predictions based upon quantum theories of electron-surface scattering (the modified theory of Sheng, Xing and Wang, the theory of Tesanovic, Jaric and Maekawa, and that of Trivedi and Aschroft). From topographic images of the surface recorded with a Scanning Tunneling Microscope, we determined the rms roughness amplitude, δ and the lateral correlation length, ξ corresponding to a Gaussian representation of the average height-height autocorrelation function, describing the roughness of each sample in the scale of length set by the Fermi wave length. Using (δ, ξ) as input data, we present a rigorous comparison between resistivity data and predictions based upon the theory of Calecki as well as quantum theoretical predictions without adjustable parameters. The resistivity was measured on gold films of different thickness evaporated onto mica substrates, between 4 K and 300 K. The resistivity data covers the range 0.1 < x(T) < 6.8, for 4 K < T < 300 K, where x(T) is the ratio between film thickness and electron mean free path in the bulk at temperature T. We experimentally identify electron-surface and electron-phonon scattering as the microscopic electron scattering mechanisms giving rise to the macroscopic resistivity. The different theories are all capable of estimating the thin film resistivity to an accuracy better than 10%; however the mean free path and the resistivity characterizing the bulk turn out to depend on film thickness. Surprisingly, only the Sondheimer theory and its quantum version, the modified theory of Sheng, Xing and Wang, predict and increase in resistivity induced by size effects that seems consistent with published galvanomagnetic phenomena also arising from electron-surface scattering measured at low temperatures.     

Low temperature resistivity minimum and its correlation with magnetoresistance in La0.67Ba0.33MnO3 nanomanganites

A systematic investigation of structural, magnetic and electrical properties of nanocrystalline La_0.67Ba_0.33MnO₃ materials, prepared by citrate gel method has been undertaken. The temperature-dependant low-temperature resistivity in ferromagnetic metallic (∼50 K) phase shows upturn behavior and is suppressed with applied magnetic field. The experimental data (<75 K) can be best fitted in the frame work of Kondo-like spin-dependant scattering, electron-electron and electron-phonon interactions. It has been found that upturn behavior may be attributed to weak spin disorder scattering including both spin polarization and grain boundary tunneling effects, which are the characteristic features of extrinsic magnetoresistance behavior, generally found in nanocrystalline manganites. The variation of electrical resistivity with temperature in the high temperature ferromagnetic metallic part of electrical resistivity (75K<T<T_P) has been fitted with grain/domain boundary, electron-electron and magnon scattering mechanisms, while the insulating region (T>T_P) of resistivity data has been explained based on adiabatic small polaron hopping mechanism.     

Influence of Sb doping on crystal structure and electrical property of SnO2 nanoparticles prepared by chemical coprecipitation

Sb doped SnO₂ (ATO) nanoparticles with Sb doping concentrations ranging from 0% to 20% (Sb/Sb+Sn) have been prepared by chemical coprecipitation using metallic Sn and SbCl₃ as raw materials. The influence of Sb doping concentration on crystal structure and electrical property was studied in detail. Results indicated that all ATO nanoparticles possessed the same tetragonal rutile structure as that of bulk SnO₂. The average crystal size of the ATO nanoparticles decreased from 16 to 7 nm by increasing the Sb doping concentration. The unit-cell volume of ATO nanoparticles was either expanded or contracted, strongly depending on the Sb doping concentration. The electrical resistivity decreased sharply from 111 to minimum of 1.05 Ω cm when the Sb doping concentration was increased from 0% to 15% and then increased slightly to 1.42 Ω cm when the Sb doping concentration was increased from 15% to 20%. Finally, high resolution X-ray photoelectron spectroscopy (XPS) measurement was employed to investigate the valence state of Sb in samples with various Sb doping levels.     

Correlation of electrical and thermalphysical properties of La0.85Ag0.15MnO3 manganite

The relationship of electrical and thermal properties of manganites has been traced through the analysis of temperature dependence of the La_0.85Ag_0.15MnO₃ resistivity. The discussion of results has been held on the basis of percolation theory in the framework of the phase-layered manganite. A behavior of the heat capacity, as well as a change in magnetic entropy can be predicted from the analysis of temperature and magnetic-field dependences of resitivity.     

Periodic Homogenization for Inner Boundary Conditions with Equi-valued Surfaces: the Unfolding Approach

Making use of the periodic unfolding method, the authors give an elementary proof for the periodic homogenization of the elastic torsion problem of an infinite — dimensional rod with a multiply-connected cross section as well as for the general electroconductivity problem in the presence of many perfect conductors (arising in resistivity well-logging). Both problems fall into the general setting of equi-valued surfaces with corresponding assigned total fluxes. The unfolding method also gives a general corrector result for these problems.     

Effect of helium ion irradiation on the structure and electrical resistivity of nanocrystalline Cr–N and V–N coatings

The structural stability and electrical resistivity of nanocrystalline Cr–N and V–N coatings prepared by ion beam-assisted deposition were studied. The results showed that under helium ion irradiation up to doses of 1.0^.10¹⁷ ion/cm² the fine-crystalline objects successively increase their resistance without apparent structural changes. The subsequent dose increase leads to gas-vacancy void formation and chromium nitride structure destruction. The presence of the initial closed porosity in vanadium nitride favors its structural stability at investigated maximum damage doses.     

Correlation study of structural,electrical and mechanical properties of quenched tin–zinc–cadmium solder alloys

It is important, for electronic application, to decrease the melting point of SnZn₉ solder alloy because it is too high as compared with the most popular eutectic Pb–Sn solder alloy. Adding Cd causes structural changes such as phase transformations, dissolution of atoms and formation of Cd crystals in the quenched SnZn₉ alloy, and its physical properties are affected by this change. For example, the melting point is decreased towards the melting point of the Pb–Sn eutectic alloy, or even much less. The structure, electrical and mechanical properties of quenched Sn_{91? x} Zn₉Cd _x (x?=?0 or x?≥?5) alloys have been investigated. Adding Cd to a quenched SnZn₉ alloy increases its electrical resistivity and decreases its elastic modulus and internal friction. The Sn₇₁Zn₉Cd₂₀ alloy has the lowest melting point (162 °C) and electrical and internal frictions as compared with commercial Pb–Sn solder alloys.