Temperature Dependence Of Specific Resistance Research Articles

Mobile oxygen in layered nickelates of perovskite-type

The influence of the different types of oxygen on the structure and electrical conductivity of the perovskite-type nickelates were investigated. The nickelates La2NiO4+δ, La0,6Sr1,4NiO4–δ, Sr3Al0,75Ni1,25O7–δ were synthesised using the solidstate reaction route. Phase composition was determined by X-ray powder diffraction analysis. The iodometric titration technique was used to specify the oxygen content of the powders. Oxygen desorption and absorption, including oxygen index variation, were investigated by oxygen solid electrolyte coulometry (OSEC). Electroconductive properties of samples were studied by a standard DC four-point method. Utilizing OSEC technique, three mobile and one regular type of oxygen were observed in the perovskite layered nickelates with P/RS and 2P/RS structure. These four types of mobile oxygen differ in the binding energy to the crystal lattice and crystallographic positions. The desorption-sorption processes of various types of mobile oxygen have different effects on the thermal expansion of crystal lattice parameters. The regular oxygen, occupying the apex of octahedron, affects the lattice parameters most prominently. This type of oxygen changes the character of the temperature dependence of specific resistivity sufficiently. Interstitial oxygen does not yield such anomalies.

Charge transfer processes in granulated Mg3Sb2 particles

In the article, temperature dependence of specific resistance (ρ), concentration of charge carriers (n) and mobility (<) was studied experimentally at T=300-700 K to study charge transfer processes in granulated Mg3Sb2 particles. The research results were explained on the basis of the charge transfer mechanism in Mg3Sb2 particles. In particular, at the initial stage of temperature increase, Т≤375 К, localized traps with energy level Ein appear in the interparticle boundary areas of the heated part of the sample. When charge carriers are trapped in them, ρ increases sharply, and n decreases. In the later stages of temperature increase, the thermal phenomenon increases along the length of the sample. In this process, localized traps with energy level Ein appear successively in the interparticle boundary regions located along the length of the sample. In relation to the charges held in them, the concentration of the generated charge carriers n increases in accordance with the increase in temperature, in this case ρ changes steadily. The increase of the potential barrier height in the interparticle boundary regions from φ ~ 0.411 eV to 0.91 eV confirms the above considerations. In addition, under the influence of temperature, the particle size and impurity ionization in the interparticle boundary areas or thermal fluctuations of the crystal lattice decrease the free movement path of the carriers. This leads to a decrease in µ at T=300-700 K.

Features of the Structure and Physical-Chemical Properties of Poly-Ortho-Toluidine Doped with Toluenesulfonic Acid


 Features of crystal structure, electrical conductivity and thermal stability of poly-ortho-toluidine (PoTi) samples, obtained with method of oxidative polymerization in the environment of sulfuric and toluenesulfonic acids (TSA), were investigated. It was discovered that PoTi-TSA samples are characterized withhigh crystallinity. According to the physico-chemical analysis, doping samples with TSA causes increase of PoTi thermal stability, electrical conductivity and sensor sensitivity on the contrary to samples doped with sulfuric acid. Based on temperature dependence of specific resistance, were calculated the values of the conductivity activation energy, which are within the limits of 0.2-0.4 eV depending on the type of dopant.

Control of Electrical and Thermal Properties by 8 vol% Al<sub>2</sub>O<sub>3</sub> Distribution States in Zn–50Sn for AC-Low Voltage Fuses

The addition of 8 vol% Al2O3 in Zn­50mass%Sn, was carried out for the control of electrical and thermal properties, for Pb-free fuse elements used in electric power line. The distribution-control of Al2O3 particles in Zn­50Sn was carried out by the varying process parameters such as the temperature and period for Al2O3-addition and -stir in its melt or semi-solid. Homogeneous and heterogeneous Al2O3-distributions were achieved in microstructure consisting of primary Zn and eutectic, which meant the location of Al2O3 in both regions and only eutectic in constituent phases, respectively. The temperature dependence of specific resistivity, thermal conductivity, specific heat and density was measured for electrical and thermal calculations to obtain the temperature distribution in fuses. The values on their properties were determined depending on Al2O3 distributed states in alloys. Both the melt and un-melt down performance for AC-low voltage fuse elements could be satisfied on both Zn­50Sn alloys with different distribution of Al2O3, and the superior performance was shown in the homogeneously Al2O3 distributed alloy. [doi:10.2320/matertrans.MBW201303]

Features of the specific resistance of nanocomposite films fabricated from multiwall carbon tubes by means of a directed spinning chuck

Nanocomposite films are produced on the basis of carbon multiwalled nanotubes (MWNTs) and polymer (carbon MWNTs/polymer, 95/5 mass %). The nanocomposite is deposited in the liquid phase on a paper substrate by a directed spinning chuck. The temperature dependence of specific resistance of the obtained films along and across the nanotube orientation is studied in the range T = 20−140°C. Irreversible transitions from semiconductor-to metal-type conductivity are observed.

Current flow by metallic shunts in alloyed ohmic contacts to wide-gap semiconductors

A mechanism of current flow across alloyed ohmic contacts in lightly doped wide-gap A3B5 semiconductors has been investigated experimentally. Changes in the current–voltage and capacity–voltage characteristics of semiconductor–metal structures have been retraced on continuous heating, the semiconductors being GaAs and GaP and the metals In and Au. Furthermore, the temperature dependence of specific resistance has been studied in the 77–450 K range for In–GaN–In, In–GaP–In and In–GaAs–In ohmic contacts. A new mechanism of current flow across ohmic contacts has been proposed that lies in the suggestion that ohmic contacts in the In–GaN and In–GaP structures containing high-density dislocations should be formed by conducting metallic shunts that are connected across the space-charge layer. The shunts originate due to indium-atom precipitation on dislocations or other imperfections, the specific contact resistance being increased with temperature. In contrast, the shunts are of no importance at low dislocation density, for instance in In–GaAs structures, and the current flow mechanism is typical of Schottky diodes (thermionic or field emission at a certain carrier concentration in semiconductors).

Electrical and Thermal Characteristics of Pb-Free Sn-Zn Alloys for an AC-Low Voltage Fuse Element

The temperature dependence of specific resistivity and thermal conductivity for some Sn-Zn alloys was measured to use their values in electrical and thermal calculations on the basis of Ohm’s and Fourier’s laws, in order to obtain the temperature-distribution in lead-free fuse elements of electric power line. The interaction between microstructures and their properties was also investigated in Sn-Zn alloys. Specific resistivity and thermal conductivity could be estimated as a function of temperature and alloy composition in the compositional ranges classified from the standpoint of continuity or non-continuity of constituent phases such as primary Zn, Sn-solid solution and eutectic in microstructures of Sn-1 to 100Zn alloys. In the proposed estimations, not only volume fraction of Zn and Sn-solid solution phases but morphologies of both phases were considered in Sn-Zn alloys. [doi:10.2320/matertrans.48.1105]

Anomalous charge carrier transport phenomena in highly aluminum doped SiC

Temperature dependant Hall effect measurements were performed on aluminum doped SiC samples with specific resistivities between 8 Ωcm and 0.1 Ωcm. In all samples indications for impurity conduction at low temperatures were found. In low doped samples, a sharp transition between the impurity conduction transport regime and the hole conduction regime is visible in the temperature dependence of specific resistivity, charge carrier concentration and mobility. In highly doped samples (ρ < 0.2 Ωcm), this transition is no longer confined to a small temperature range and much less abrupt. We conclude that the impurity conduction is still present at high temperatures in highly aluminum doped SiC so that at least two competing transport mechanisms are present simultaneously in these samples. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Insulating GaN:Zn layers grown by hydride vapor phase epitaxy on SiC substrates

Fabrication of high-performance GaN microwave devices, which are the excellent candidates for new generation of high-power solid-state components, requires insulating GaN substrate materials. Due to lack of bulk GaN crystals and particularly lack of semi-insulating GaN substrates, we propose insulating GaN layers on silicon carbide as substrates for the fabrication of GaN-based microwave devices. In this work, we demonstrate insulating GaN layers on silicon carbide substrates. Insulating GaN layers doped with zinc were grown on silicon carbide substrates by hydride vapor phase epitaxy. High crystal quality of the grown material was proved by x-ray diffraction measurements showing the full width at a half maximum of ω-scan rocking curve of about 100 arcsec. Temperature dependence of specific resistivity of the GaN:Zn layers was measured in the temperature range from 200 to 500 K. The value of the specific resistivity was found to be 1012 Ω cm at 300 K and 109 Ω cm at 500 K.

Effect of Cold Acclimation on Bulk Tissue Electrical Impedance

The resistive and reactive components of electrical impedance were measured for birdsfoot trefoil (Lotus corniculatus L.) stems at freezing temperatures to -8 degrees C. As temperature decreased the specific resistance at frequencies between 49 hertz and 1.11 megahertz of stems from cold acclimated plants increased more rapidly than from nonacclimated plants. This temperature dependence of specific resistance could be characterized by an Arrhenius activation energy; cold acclimated stems had a larger Arrhenius activation energy than nonacclimated stems. The low frequency resistance is believed to characterize the extracellular region of the stems and the high frequency resistance is believed to characterize the intracellular region of the stems. Cold acclimation increased the intracellular but not the extracellular resistance at nonfreezing temperatures. Cold acclimated stems were not injured by freezing to -8 degrees C and thawing, but nonacclimated stems were injured by freezing to temperatures between -2.2 and -5.6 degrees C and thawing. Injury to nonacclimated stems at freezing temperatures below -2.2 degrees C was indicated by a decrease in the ratio of resistance at 49 Hz to that at 1.11 megahertz.

Structure and electrical resistance of thin scandium films (III). Study on electrical properties

AbstractThe specific resistance‐thickness of ScHx (vacuum 10−5 to 5 · 10−6 Torr) and Sc films (vacuum 1 · 10−8 to 3 · 10−8 Torr) relationships have been obtained by keeping a record of a film resistance directly in the course of condensation. The results are discussed according to the theory FUCHS‐SONDHEIMER (ScHx, Sc) and MAYADAS‐SHATZKES (Sc) assuming a diffuse scattering of the carriers (P = 0) on the external surface of the films. A mean free path of the current carriers is 188 to 355 Å (T ⋍ 300 K) for ScHx and 400 Å with grain‐boundary scattering parameter from 0.1 to 0.3 for Sc. The temperature dependence of specific resistivity of Sc films was obtained in the interval from 300 to 650 K during the annealing in vacuum 5 · 10−9 Torr.