Electrical Resistivity Characteristics Research Articles

Design of compositions of low-melting phosphate glass-enamel coatings based on composites in the R 2O-TiO2-Al2O3-B2O3-P2O5 system for aluminum

The pseudoternary system intended for synthesis of low-melting phosphate glass-enamel coatings for aluminum articles has been studied. The optimum ratio between concentrations of alkali oxides providing the maximum mixed-alkali effect has been determined and its influence on the properties of enamels (such as chemical durability, electrical resistivity, thermal expansion, and fusibility characteristics) has been investigated.

High temperature ReCOB piezocrystals: Recent developments

Piezoelectric sensors for high temperature applications have attracted attention due to their simplistic structure, fast response time and ease of integration. In this article, oxyborate ReCa4O(BO3)3 (Re: rare earth element; abbreviated as ReCOB) piezoelectric crystals were surveyed for their potential use in high temperature sensing applications. In contrast to quartz and GaPO4 crystals, no phase transformation(s) are observed prior to their melting points, being in the order of ∼1500°C. The electrical resistivity, dielectric, piezoelectric properties and resonance-impedance characteristics were studied as a function of temperature over the range of Room Temperature (RT) to 950°C. The resistivity of ReCOB was found to be ∼2×108Ohmcm at 800°C, two orders higher than langasite, another widely studied crystal system. The electromechanical coupling factors k26 and piezoelectric coefficients d26 were found to be >20% and >10pC/N, respectively, with the variation being <20% over the studied temperature range. The resonance frequency for width shear vibration was found to decrease linearly with increasing temperature for YCOB crystals, with the Temperature Coefficient of Frequency (TCF) in the order of 70ppm/K, while for NdCOB crystals, a nonlinear behavior was observed, demonstrating a potential zero TCF crystal cut. The high resistivity, high piezoelectric properties and low mechanical and dielectric losses, together with temperature independent characteristics, demonstrate that oxyborate crystals are promising candidates for high temperature sensing applications.

Piezoresistive Microcantilevers From Ultrananocrystalline Diamond

This paper reports on the temperature-dependent electrical resistivity and piezoresistive characteristics of boron-doped ultrananocyrstalline diamond (UNCD) and the fabrication of piezoresistive microcantilevers using boron-doped and undoped UNCD. The devices consist of 1-μm-thick doped UNCD on either 1- or 2-μm-thick undoped UNCD. The electrical resistivity of doped UNCD is 0.1 Ω · cm at room temperature, which is five orders of magnitude smaller than the electrical resistivity of undoped UNCD. Over the temperature range of 25°C-200vC, the doped UNCD has a temperature coefficient of electrical resistance of (-1.4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ) per °C. The doped UNCD exhibits a significant piezoresistive effect with a gauge factor of 7.53 ± 0.32 and a piezoresistive coefficient of 8.12 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> Pa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at room temperature. The piezoresistive properties of UNCD are constant over the temperature range of 25°C-200°C. Microcantilevers having a length of 300 μm have a deflection sensitivity of 0.186 mΩ/Ω per micrometer of cantilever end deflection. These measurements of electrical and piezoresistive properties of doped UNCD could aid the design of future diamond microsystems.

Anomalous Hall effect and perpendicular magnetic anisotropy in Sm 28Fe 72 and Sm 32Fe 68 thin films

Sm 28Fe 72 and Sm 32Fe 68 films of 100 nm thickness were grown using DC magnetron sputter deposition and their structure, magnetization, electrical and Hall resistance characteristics were investigated. An increase in electrical resistivity from 4.75×10 −6 to 5.62×10 −6 Ω m and from 2.26×10 −6 to 2.84×10 −6 Ω m for Sm 28Fe 72 and Sm 32Fe 68 films, respectively, with decrease in temperature from 300 to 40 K is attributed to the strain induced anisotropy that dominates at lower temperatures. The positive extraordinary Hall coefficients ( R S ) are observed for both films at 300 and 80 K. The existence of hysteresis indicates that Sm 28Fe 72 and Sm 32Fe 68 films possess perpendicular anisotropy at 300 K. Hysteresis loop becomes narrow at 80 K for both Sm 28Fe 72 and Sm 32Fe 68 films. Magnetization measurements at 300 K exhibiting small coercive field values of 31 and 49 Oe for Sm 28Fe 72 and Sm 32Fe 68 films, respectively, confirm the existence of perpendicular anisotropy at 300 K.

Thermal and Electrical Conductivities of Carbon Fibers and Carbon Nanotubes Incorporated Polyurethanes Composites

Single filler polyurethane composites with carbon fibers (CFs) and multi-walled carbon nanotubes (MWNTs) were prepared by melt mixing methods and its thermal as well as electrical resistivity characteristics were investigated. The influences of fillers and mixing methods on thermal and electrical conductivity of CF/- and MWNT/polyurethane composites were investigated and the result shows that the addition of carbon fillers improved the thermal conductivity of the polyurethane composites. Higher filler concentration results in better thermal conductivity because better formation of thermally conductive networks along polymer matrix to ensure the thermal was conducted through the matrix and the network along the polymer composites. The presence of carbon additives improves the electrical resistivity of the materials as well. The present study revealed the potential of carbon as agent for better thermal and electrical conductivities and their properties depend strongly on the dispersion and distribution of the fillers in the polymer matrix.

GEO-ELECTRICAL SURVEY ON THE SOIL OF AN APRICOT ORCHARD GROWN UNDER SEMI-ARID CONDITIONS

A geo-electrical survey, combined with direct measurements on soil samples, was performed to study spatial relationships among electrical resistivity (p), hydro-pedological parameters, and root characteristics. The trial was carried out on the soil (WRB: Haplic Regosols) of an apricot orchard grown in a semi-arid climate, cover-cropped, and micro-irrigated. Three 2D geo-electrical tomographies were performed in the Wenner and dipole-dipole array (electrode spacing of 25 cm). Soil samplings were carried out from vertical trenches excavated directly below the respective geo-electrical profiles. Direct measurements of bulk density, grain size distribution, volumetric water content (θ), electrical soil conductivity (EC 1:1 , EC 1:2.5 ), stone content, and root biomass were performed on the soil samples in situ and in the laboratory. Hydraulic saturation (HS) and soil porosity (Φ) were also calculated. Statistical analyses performed between the geo-electrical signals (p) and soil data showed a univariate relationship with EC 1:2.5 . Multivariate relationships among p, EC 1:1 , and HS were also found. The significant relationship found between p and soluble salt content proves the usefulness of the geo-electrical technique in the medium-scale assessment of the spatial variability of salt accumulation processes in heterogeneous tree orchard systems.

Solid-phase synthesis of cobalt germanides in epitaxial Ge/β-Co(001) and Ge/α-Co(100) nanofilms

The experimental results of a study of solid-state synthesis of cobalt germanides in epitaxial Ge/α-Co(001) and Ge/β-Co(110) nanofilms are presented. For both polymorphic modifications of cobalt, it is demonstrated that the Co5Ge7 phase occurs at ∼ 275 ◦C. When the annealing temperature increases to ∼ 300 ◦C, the CoGe2 phase forms, which sharply reduces the electric resistance and magnetic characteristics of the samples. The order of the formation of phases and the temperatures at which the phases are formed are not changed based on the polymorphic modification of cobalt.

Finite element analysis of CICC joints in SST-1

We have analysed the newly designed CICC joints in SST-1 using finite element method for their in-situ performance in SST-1 operation. Cool-down characteristics, thermo-structural stresses due to cool-down and electromagnetic forces, electrical resistance characteristics have been investigated. These results will be discussed in this paper.

Large superplastic strain in non-modulated epitaxial Ni–Mn–Ga films

The phase transformation and superplastic characteristics of free-standing epitaxial Ni–Mn–Ga stripes are reported. The stripes are prepared by micromachining a 1μm thick Ni–Mn–Ga film sputter-deposited on a single crystalline MgO (100) substrate using optical lithography and a Chromium-based sacrificial layer technology. The stripes are oriented at angles of 0 and 45 degrees with respect to the Ni–Mn–Ga unit cell. Electrical resistance versus temperature characteristics reveal a reversible thermally induced phase transformation between 169∘C and 191∘C. Stress-strain measurements are performed with the stress applied along the [100]Ni−Mn−Ga as well as [110]Ni−Mn−Ga direction. Depending on the orientation, the twinning stress ranges between 25 and 30MPa, respectively. For the [100]Ni−Mn−Ga and [110]Ni−Mn−Ga directions, superplastic behaviour with a strain plateau of 12% and 4% are observed, respectively, indicating stress-induced reorientation of non-modulated martensite variants.

Characteristics of Electrical Skin Resistance at Acupuncture Points in Healthy Humans

The aim of this study was to evaluate the phenomenon of electrical skin resistance (ESR) changes at different acupuncture points (APs). This single-blinded study was performed at the hospital of the University of Munich. Six common APs were measured (TE5, PC6, LU6, ST36, SP6, GB39) in 53 subjects. Subgroups were formed with varying time intervals for follow-ups (1 minute, 1 hour, 1 week) and a varying grade of reduction of the stratum corneum. Electrical skin resistance measurements (ESRMs) were taken from a skin area of 6 x 6 cm using an array consisting of 64 (8 x 8) electrodes. The electrodes corresponding to the AP were located and the ESRM results were compared to those of the surrounding electrodes. The methodological setting made it possible to minimize major influence factors on electrical skin impedance measurements. A total of 631 ESRMs was evaluated: In 62.8% of the measured APs, no significant ESR difference was found. In 234 (37.2%) of the ESRMs, the ESR at the AP was significantly different from the surrounding skin area, with 163 (25.9%) points showing a lower and 71 (11.3%) points showing a higher ESR. Reproducibility was extremely high after 1 minute but was low after 1 hour and 1 week. This study shows that electrical skin resistance at APs can either be lower or higher compared to the surrounding area. The phenomenon is characterized by high short-term and low long-term reproducibility. Therefore, we conclude that APs might possess specific transient electrical properties. However, as the majority of the measured APs did not show a changed ESR, it cannot be concluded from our data that electrical skin resistance measurements can be used for acupuncture point localization or diagnostic/therapeutic purposes.

Electronic transport and magnetic properties of the perovskites La 0.8Sr 0.2Co 1− xFe xO 3; x ≤ 0.3

Transport and magnetic properties of LaCoO 3-based compounds, doped with 20% Sr and 2.5, 5, 10, 15, 20 and 30% Fe, were investigated by means of magnetization, resistivity and magnetoresistance measurements as well as by 57Fe Mössbauer spectroscopy. While the temperature dependence of the dc and ac magnetic susceptibilities reveals the presence of magnetic phase separation accompanied by spin-glass and cluster-glass behavior, the electrical resistivity and magnetoresistance characteristics indicate that the mesoscopic structure of the present compounds is rather well described as consisting of ferromagnetic, metallic grains embedded in an insulating matrix. The effect of the partial Co → Fe substitution on the bulk magnetic and transport properties, as well as on the local state of Co and Fe ions is discussed.

Structural and dielectric properties of some epiclon-based polyimide films

AbstractSurface and electrical properties of two flexible and cross-linked epiclon based polyimide films were investigated. Surface tension measurements indicate an increased hydrophobicity due to both isothermal treatment - which induces imidization and cross-linking - and to the chemical structure, characterized by the different number of ether linkages in the polyimide backbone. Morphology of film surfaces, modified by plasma treatment, shows high roughness and, implicitly, improved adhesion, as required in electronics. The studied polyimides exhibit low dielectric constants and dielectric losses, comparatively to conventional aromatic polyimides. The electrical conductance and resistivity characteristics of these polymers recommend them as good insulators for dielectric layers in microelectronic applications.

Effect of ultraviolet irradiation on electrical resistance and phase transition characteristics of thin film vanadium oxide

Metal-insulator transitions in strongly correlated oxides such as vanadium oxide (VO2) are of great scientific and technological interest. Due to the presence of multiple oxidation states, synthesis of high-quality VO2 films on substrates with the desired phase transition characteristics such as large jumps in phase transition resistance is a challenge. We show that the resistance ratio across the metal-insulator transition as well as the resistance of thin film VO2 can be modulated at relatively low temperatures by the use of ultraviolet irradiation. The enhanced oxygen incorporation due to creation of excited oxygen species enables controllably tunable stoichiometry.

Characteristics of microstructure and electrical resistivity of inkjet-printed nanoparticle silver films annealed under ambient air

The microstructure and electrical resistivity of inkjet-printed silver (Ag) films annealed under ambient air were characterized. Analyses of the impurity amounts in the films using secondary-ion mass spectrometry showed that the decomposition temperature of the capping molecules was just below 170°C. Both the characteristics of the microstructure and electrical resistivity when annealed at low temperatures (lower than the decomposition temperature) were significantly different from those when annealed at high temperatures. The results show that neither microstructural features, such as grain size, nor the amounts of impurities can explain both the magnitude and characteristic decrease in electrical resistivity. The changes in electrical resistivity can be described using exponential decay kinetics. The corresponding activation energy of 0.44 eV when annealed at the high temperatures is explained by the migration of point defects such as vacancy–oxygen pairs. On the other hand, negligible dependence on temperature was identified when annealed at low temperatures, which was attributed to decomposition of the capping molecules. The results indicate the importance of controlling the defects of nanoparticles and the properties of capping molecules from the viewpoint of electrical optimization of metallization fabricated using inkjet printing.

Strain-dependent electrical resistance of multi-walled carbon nanotube/polymer compositefilms

The strain-dependent electrical resistance characteristics of multi-walled carbon nanotube(MWCNT)/polymer composite films were investigated. In this research, polyethylene oxide(PEO) is used as the polymer matrix. Two representative volume fractions ofMWCNT/PEO composite films were selected: 0.56 vol% (near the percolation threshold)and 1.44 vol% (away from the percolation threshold) of MWCNT. An experimental setupwhich can measure electrical resistance and strain simultaneously and continuously hasbeen developed. Unique and repeatable relationships in resistance versus strain wereobtained for multiple specimens with different volume fractions of MWCNT. The overallpattern of electrical resistance change versus strain for the specimens tested consists oflinear and nonlinear regions. A resistance change model to describe the combination oflinear and nonlinear modes of electrical resistance change as a function of strain issuggested. The unique characteristics in electrical resistance change for differentvolume fractions imply that MWCNT/PEO composite films can be used as tunablestrain sensors and for application into embedded sensor systems in structures.

PIV Study on Buoyant Bubble Flows in a Small Electrolytic Cell

Water electrolysis has been recently recognized as a very important technology for hydrogen production. It has been well-known that electrolytic bubbles cause an increase in effective resistivity of the electrolyte, and there have been many electrochemical studies of the bubble dispersion effects on electrolysis characteristics. There are, however, very few studies that measure the growing phenomenon of bubbles from generation to departure on an electrode surface, the bubble rising velocity distribution and the void fraction in the interelectrode gap; moreover, their effects on the electric resistance characteristics have not been discussed extensively. We conducted an experimental study focusing on a small-scale electrolytic cell for hydrogen production in order to resolve the these issues, and discussed the fluid forces (surface tension, buoyancy, drag) acting on hydrogen bubbles from a viewpoint of gas-liquid two-phase flow. We used a PIV technique with a high-speed video camera and a shallow focal image system. As a result, we were able to successfully capture the images of hydrogen bubbles during the growth, and found that there was a linear relationship between log(We) and log(Re), where We is the Weber number and Re is the Reynolds number for a circulation type of the electrolytic cell. We also found an optimal gap between two electrodes when the flow pattern changes from bubbly flow to plug flow.

Effects of Post-Annealing on the Electrical and Optical Properties of ZnO Thin Films Grown on Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Substrates by Atomic Layer Epitaxy

Influence of nitrogen and oxygen annealing atmospheres on the carrier concentration, carrier mobility, electrical resistivity and PL characteristics as well as the crystallinity of ZnO films deposited on sapphire substrates by atomic layer deposition (ALD) were compared. X-ray diffraction (XRD) and photoluminescence (PL) analyses, and Hall measurement were performed to investigate the crystallinity, optical properties and electrical properties of the ZnO thin films, respectively. The UV emission intensity for oxygen annealing is stronger than that for nitrogen annealing in the case of annealing at 600°C, but the difference decreases with the Increase of annealing temperature. The strongest UV emission is obtained by oxygen annealing at 800°C. However, from the viewpoint of electrical resistivity annealing at 1,000°C in either an oxygen or a nitrogen atmosphere is more desirable. Taking both the PL and electrical properties into consideration it may be concluded that optimum annealing condition for ZnO thin films grown on the sapphire substrate by ALD is an annealing temperature of 900°C and an annealing atmosphere of oxygen although the effects of annealing atmosphere on the optical and electrical properties are not so significant.

On the effect of acetic acid on physical properties of chemically sprayed fluorine-doped ZnO thin films

Fluorine-doped zinc oxide (ZnO:F) thin films onto sodocalcic glass substrates, starting from a highly concentrated starting solution (0.4 M) containing zinc acetate and hydrofluoric acid diluted in a mixture of deionized water, acetic acid , and methanol, using the chemical spray deposition technique, were deposited and characterized. The effect of the acetic acid content in the starting solution, and the substrate temperature on the electrical resistivity, structure, morphology and optical characteristics was studied. The samples were polycrystalline in nature, but as the acetic acid content in the starting solution increases, the preferential orientation shows a switching from (002) to (101). For a predetermined deposition temperature, as the acetic acid content increases, the film resistivity values show an increase. The minimum resistivity in the order of 6 × 10 − 3 Ω cm was found for the films deposited with the lowest acetic acid content used. The surface morphology varies from agglomerated grains to rod-like shaped grains as a function of the acetic acid content.

Thermo-chemical properties and electrical resistivity of Zr-based arsenide chalcogenides

abstractTernary phases in the systems Zr–As–Se and Zr–As–Te were studied using single crystals of ZrAs1.40(1)Se0.50(1) and ZrAs1.60(2)Te0.40(1) (PbFCl-type of structure, space group P4/nmm) as well as ZrAs0.70(1)Se1.30(1) and ZrAs0.75(1)Te1.25(1) (NbPS-type of structure, space group Immm). The characterization covers chemical compositions, crystal structures, homogeneity ranges and electrical resistivities. At 1223 K, the Te-containing phases can be described with the general formula ZrAsxTe2–x, with 1.53(1)≤x≤1.65(1) (As-rich) and 0.58(1)≤x≤0.75(1) (Te-rich). Both phases are located directly on the tie-line between ZrAs2 and ZrTe2, with no indication for any deviation. Similar is true for the Se-rich phase ZrAsx–ySe2–x with 0.70(1)≤x≤0.75(1). However, the compositional range of the respective As-rich phase ZrAsx–ySe2–x (0.03(1)≤y≤0.10(1); 1.42(1)≤x≤1.70(1)) is not located on the tie-line ZrAs2–ZrSe2, and exhibits a triangular region of existence with intrinsic deviation of the composition towards lower non-metal contents. Except for ZrAs0.75Se1.25, from the homogeneity range of the Se-rich phase, all compounds under investigation show metallic characteristics of electrical resistivity at temperatures >20 K. Related uranium and thorium arsenide selenides display a typical magnetic field-independent rise of the resistivity towards lower temperatures, which has been explained by a non-magnetic Kondo effect. However, a similar observation has been made for ZrAs1.40Se0.50, which, among the Zr-based arsenide chalcogenides, is the only system with a large concentration of intrinsic defects in the anionic substructure.

Structural phase transformations and physical properties of intercalation compounds in the Cr0.5Ti(Se1−x Tex)2 system

The atomic structure and magnetic and electric properties of the Cr0.5TiSe2-Cr0.5TiTe2 system of intercalated phases were studied in detail by gradually replacing selenium by tellurium. It was revealed that this replacement changes the crystalline structure from monoclinic in the initial compounds to hexagonal in the compounds containing various types of chalcogen atoms; this is accompanied by disordering of chromium atoms in the van der Waals gaps. The electrical resistance and magnetic characteristics vary nonmonotonically on replacement of selenium by tellurium, which is associated with a change in the degree of atomic disordering during the transition from Cr0.5TiSe2 to Cr0.5TiTe2.