Dc Resistivity Measurements Research Articles

Dielectric property determination of hybrid Al2O3-filled MWCNT buckypaper by the rectangular cavity perturbation technique

This study investigated the complex dielectric permittivity of freestanding multiwalled carbon nanotube buckypaper (MWCNT-BP) and a synthesized hybrid alumina-filled buckypaper (Al2O3-BP) composite with different alumina loadings (5–30 wt%). The non-destructive microwave transmission technique for complex permittivity determination involving cavity perturbation was employed to characterize a set of Al2O3-BP sheets. This was done by filling a rectangular cavity resonator with a standard dielectric Teflon sample and then performing permittivity measurements for the buckypaper (BP) samples in the X-band frequency range (7–12 GHz). Field-emission scanning electron microscopy (FESEM) was used to analyze the morphology of the MWCNT-BP and the alumina-loaded BP composites. DC electrical resistivity measurements clearly demonstrated conductor–insulator transition. The effect of alumina loadings on the dielectric properties of the synthesized hybrid Al2O3-BP sheet is discussed.

Effect of hydrostatic pressures on the superconductivity of new BiS2 based REO0.5F0.5BiS2 (RE=La, Pr and Nd) superconductors

We study the effect of hydrostatic pressure on superconductivity of new BiS2 based layered REO0.5F0.5BiS2 (RE=La, Pr, and Nd) compounds through the measurements of dc electrical resistivity. The REO0.5F0.5BiS2 (RE=La, Pr and Nd) compounds synthesized by solid state reaction route via vacuum encapsulation are crystallized in the tetragonal P4/nmm space group. At ambient pressure the superconducting transition onset temperatures (Tconset) are 2.7K, 3.5K and 4.5K, which are enhanced substantially under external hydrostatic pressure to 10.5K, 7.8K and 7.5K for LaO0.5F0.5BiS2, PrO0.5F0.5BiS2 and NdO0.5F0.5BiS2 respectively at 1.68GPa. The normal state electrical resistivity decreases with applied pressure for REO0.5F0.5BiS2 (RE=La, Pr and Nd). The electrical resistivity under magnetic field and applied pressure has been measured to estimate upper critical field Hc2(0), the values of which are 15.9Tesla, 8.8Tesla and 8.2Tesla for LaO0.5F0.5BiS2, PrO0.5F0.5BiS2 and NdO0.5F0.5BiS2 compounds. Substantial enhancement of superconductivity under moderate pressures in studied new BiS2 based superconductors call for the attention of condensed matter physics community.

Effects of thickness variation on properties of ZnO:Al thin films grown by RF magnetron sputtering deposition

Polycrystalline transparent conductive aluminum doped zinc oxide (ZnO:Al) films, have been grown successfully on glass and silicon substrates by RF magnetron sputtering technique at room temperature. The thickness effect on the structural, optical and electrical properties of these samples is then studied. The structural characterization was carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM).The dc electrical resistivity measurement is achieved in dark at room temperature using four-point probes technique. UV–visible spectroscopy was carried out for the optical characterization. The results show that all the deposited films present a crystalline wurtzite structure with a strong preferred (002) orientation. The intrinsic compressive stress was found to decrease with the increase of the film thickness. The electrical resistivity decreases with the increase of the film thickness and the smallest measured value was 8×10−4Ωcm for the 1500nm thick film. The obtained ZnO:Al films, not only have an average transmittance greater than 90% in the visible region, but also have an optical band gap between 3.32 and 3.49eV depending on the film thickness.

Reliability Study on Adhesive Interconnections in Flex-to-Flex Printed Electronics Applications Under Environmental Stresses

The reliability of conductive adhesive interconnections in flex-to-flex printed electronics applications under thermal cycling and cyclic bending tests is investigated in this paper. The components under study consisted of a backplane, having screen-printed silver wiring on polyethylene terephthalate film, fabricated in a roll-to-roll process, and a flexible functional component mimic stacked on top of the backplane. Each test component contained four daisy-chained conductive adhesive interconnections, and their reliability was monitored in situ with a four-point dc resistance measurement during tests. In addition, the effect of supportive nonconductive adhesives on structure reliability was studied in various configurations. The accelerated life test results proved that the long-term reliability of the studied components can be enhanced by adding supportive adhesive between the flexible layers. In both thermal cycling and cyclic bending tests, the most reliable method was found to be the configuration with supportive adhesive around the top layer sides, attaching the two layers totally together, whereas the configuration with no supportive adhesive at all showed the worst reliability. The failure analysis emphasized that the critical factor, in terms of reliability, was silver conductor delamination from the backplane surface at the interconnection area.

Synthesis and Characterization of Screen Printed Zn0.97Cu0.03O Thick Film for Semiconductor Device Applications

The studies on doped ZnO thick films deposited over large surface area are still a very promising area of research and development. We report characteristic properties of thick film of Zn0.97Cu0.03O prepared by the economic screen printing technique. The film was characterized by XRD, SEM, diffused reflectance, FTIR, and dark resistivity measurement techniques. The XRD and SEM studies revealed polycrystalline, single phase, porous, and granular surface morphology of this Cu doped ZnO thick films. The direct band gap energy of this film determined by diffuse reflectance technique is 3.18 eV. IR transmission spectrum measured in 4000–600 cm−1 region at ambient temperature confirmed the incorporation of Cu2+ ions in ZnO lattice. The DC resistivity measurements reveal semiconducting nature of the sample with activation energy of 0.66 eV.

Structural and Electrical Properties of Li–Ni Nanoferrites Synthesised by Citrate Gel Autocombustion Method

An attempt has been made to synthesize nanocrystalline lithium-nickel ferrites with a compositional formula Li0.5−0.5xNixFe2.5−0.5xO4(wherex=0.0to 1.0 with step of 0.2) by a low temperature citrate gel autocombustion method. Single phase cubic structure is confirmed by X-ray diffraction analysis. This result demonstrates that the prepared samples are homogeneous and the sharp peaks reveal that the samples are in good crystalline form. As the Ni concentration is increased, various interesting changes in the values of the structural parameters like lattice parameter, X-ray density, bulk density, and porosity have been observed. The surface morphology of the prepared samples was studied using scanning electron microscopy (SEM). The DC resistivity measurements were carried out using two-probe method from 200°C to 600°C. The variation oflog⁡(σT)with reciprocal of temperature shows a discontinuity at Curie temperature.log⁡(σT)versus1/Tplot of the pure lithium ferrites is almost linear which indicates the Curie temperature of the pure lithium ferrites was beyond our measured temperature. The dielectric properties of these ferrites have been studied using a LCR meter from the room temperature to 700 K at various frequencies up to 5 MHz, which reveals that all the prepared samples have dielectric transition temperature around 600 K.

Highly coercive cobalt ferrite nanoparticles-CuTl-1223 superconductor composites

We explored the effects of highly coercive cobalt ferrite (CoFe2O4) nanoparticles addition on structural, morphological, and superconducting properties of Cu0.5Tl0.5Ba2Ca2Cu3O10-δ (CuTl-1223} matrix. Series of (CoFe2O4)x/CuTl-1223 (x=0 ~2.0 wt%) composites samples were synthesized and were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) absorption spectroscopy, and dc-resistivity versus temperature measurements. The magnetic behavior of CoFe2O4 nanoparticles was determined by MH-loops with the help of superconducting quantum interference device (SQUID). MH-loops analysis showed that these nanoparticles exhibit high saturation magnetization (86 emu/g) and high coercivity (3350 Oe) at 50 K. The tetragonal structure of host CuTl-1223 superconducting matrix was not altered after the addition of CoFe2O4 nanoparticles, which gave us a clue that these nanoparticles had occupied the inter-granular sites (grain-boundaries) and had filled the pores. The increase of mass density with increasing content of these nanoparticles in composites can also be an evidence of filling up the voids in the matrix. The resistivity versus temperature measurements showed an increase in zero resistivity critical {Tc(0)}, which could be most probably due to improvement of weak-links by the addition of these nanoparticles. But the addition of these nanoparticles beyond an optimum level caused the agglomeration and produced additional stresses in material and suppressed the superconductivity.

Nanostructural, magnetic and electrical properties of Ag doped Mn-ferrite nanoparticles

Nano-crystalline MnFe2−xAgxO4 (x = 0, 0.1, 0.2, 0.3 and 0.6) samples with average grain size of 4–7 nm were synthesized by a simple method based on decomposition of metal nitrates in presence of citric acid. The samples were characterized by different structural, magnetic and electrical measurements. Rietveld refinement of X-ray diffraction data confirmed cubic spinel structure of the samples. Results show that Ag doping decreases the crystallite size, magnetization and coercivity of nanoparticles. By increasing the Ag content in the samples the saturation magnetization shows interesting temperature dependent behavior. It was realized that magnetization of smaller particles show higher sensitivity to temperature variations than larger particles. DC electrical resistivity measurements in the temperature range of 300–650 K show that the resistivity first increases and then decreases by increasing the Ag content in the samples. Curie temperature (Tc) and polaron activation energy in ferromagnetic and paramagnetic regions were estimated by using resistivity curves.

Synthesis and superconducting properties of (Au)x/CuTl-1223 composites

We explored the feasibility of synthesizing (Au)x/(Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ {(Au)x/CuTl-1223};x=0, 0.5, 1.0, and 1.5wt.%, nano-superconductor composites by two steps solid-state reaction. We investigated the effect of gold (Au) nanoparticles on the structural and superconducting properties of CuTl-1223 matrix. These composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) absorption spectroscopy, ac-susceptibility (χac) and dc-resistivity (ρ) measurements. We observed the tendency of Au nanoparticles to occupy the inter-granular spaces (grain-boundaries) as the tetragonal structure of CuTl-1223 superconducting matrix remained unaltered after the addition of Au nanoparticles. The improvement in the superconducting properties after the addition of Au nanoparticles can be attributed to an increase in the inter-grains connectivity by healing up the inter-grains voids and pores by these nanoparticles. The improved inter-grains connections can facilitate the carriers transport across the inter-crystallite sites. But the superconducting volume fraction starts to be decreased after certain optimum inclusion level of Au nanoparticles, which causes the suppression of superconductivity parameters. The non-superconducting metallic Au nanoparticles reduce the superconducting volume fraction beyond certain optimum level of Au nanoparticles inclusion in superconducting state of CuTl-1223 matrix.

AC Quantum Interference Effects in Nanopatterned Nb Microstrips

The mixed-state dc voltage response of nanopatterned Nb microstrips is investigated by combined microwave (0.5 MHz—1 GHz) and dc electrical resistance measurements. The nanopatterns are arrays of symmetric grooves on the film surface fabricated by focused ion beam milling. They provide a pinning potential of the washboard type for the vortex motion. When subject to a microwave stimulus, the dc current–dc voltage curves of the microstrips exhibit Shapiro steps. The steps occur at voltages V=n V 0=n N f Φ 0, where n is an integer, N is the number of vortex rows between the voltage leads, f is the microwave frequency, and Φ 0 is the magnetic flux quantum. These steps arise as an interference effect when one or a multiple of the hopping period of the coherently moving Abrikosov vortices coincides with the period of the ac drive. When tuning the field value away from the matching field, the steps disappear due to lacking coherence in the motion of the Abrikosov vortex lattice. Dependencies of the dc critical (depinning) current on the microwave power and frequency are reported.

Superconductivity in LaPd2As2 with a collapsed 122 structure

The superconducting properties of LaPd2As2 with a collapsed tetragonal structure are reported. DC magnetization and resistivity measurements reveal that the compound is a type-II bulk superconductor below 1K. The electronic specific heat coefficient γ is found to be 5.56mJmol−1K−2. The specific heat change at the superconducting transition is 1.17, which is relatively low compared to the BCS weak coupling limit of 1.43. The density of states at the Fermi level calculated from electronic specific heat data is about 0.84 states/(eVf.u.), which may explain the low Tc of this material. These results, together with previous work on A2+M2X2 compounds, imply that the superconducting transition temperature can be tailored by proper chemical substitution.

Parallel integration of aligned carbon strings in polymer composite: Dielectrophoretic preparation, finite element simulation, and electrical characterization

We report on dielectrophoretic alignment of carbon black particles into radially arranged string‐like assemblies in oligourethane mixtures followed by photopolymerization. Using finite element modelling and optical microscopy we find significant difference in field distributions depending on the substrate beneath aligned films. On glass, the field is concentrated between the electrode tips leading to string‐like assemblies between the tips. On oxide covered silicon, the field is distributed along the electrode circumference leading to more distributed fractal assemblies. Using comprehensive dc resistance measurements and ac‐impedance spectroscopy we show that the resistance of the strings varies from 120 kΩ to 5 MΩ with a mean of 1.03 MΩ. Strings on oxide covered silicon show significantly higher resistances than the strings on glass. We also demonstrate the effect of aging and an increase in resistance through elongating aligned strings. POLYM. COMPOS., 36:1866–1874, 2015. © 2014 Society of Plastics Engineers

The influence of electron-phonon coupling and spin fluctuations on the superconductivity of the Ti-V alloys

We report a study of the normal and superconducting state properties of the Ti x V1−x alloys for x = 0.4, 0.6, 0.7 and 0.8 with the help of dc magnetization, electrical resistivity and heat capacity measurements along with the electronic structure calculation. The superconducting transition temperature T c of these alloys is higher than that of elemental Ti and is also higher than elemental V for x ≤ 0.7. The roles of electron density of states, electron-phonon coupling and spin fluctuations in the normal and superconducting state properties of these alloys have been investigated in detail. The experimentally observed value of T c is found to be considerably lower than that estimated on the basis of electron density of states and electron-phonon coupling in the x = 0.4, 0.6 and 0.7 alloys. There is some evidence as well for the preformed Cooper pair in all these Ti-V alloys in the temperature regime well above T c . Similar to x = 0.6 [Md. Matin, L.S. Sharath Chandra, R.K. Meena, M.K. Chattopadhyay, A.K. Sinha, M.N. Singh, S.B. Roy, Physica B 436, 20 (2014)], the normal state properties of the x = 0.4 alloy showed the signature of the presence of spin fluctuations. The difference between the experimentally observed T c and that estimated by considering electron density of states and electron-phonon coupling in the x = 0.4, 0.6 and 0.7 alloys is attributed to the possible influence of these spin fluctuations. We show that the non-monotonous variation of T c as a function of x in the Ti x V1−x alloys is due to the combined effects of the electron-phonon coupling and the spin fluctuations.

Effect of Chrome Coating on Resistance of Sintered Joint for ITER Central Solenoid

The ITER Central Solenoid has 36 interpancake joints. The joints are required to have a resistance below 4 nOhm at 45 kA at 4.5 K. The US ITER Project Office developed and qualified a sintered joint for the interpancake joints that consistently showed exceptionally low dc resistance of 0.13 nOhm at up to 80 kA in the self-field of about 1.5 T. To provide a good current distribution in the joint, we removed chrome plating from the strands in this area. We built and tested four samples of the sintered joints before 2012. Such a low resistance prompted an investigation of the possibility of leaving the chromium on the strands during the joint preparation and still staying well below allowable resistance. Although removal of the chrome plating is not a very labor-intensive or time-consuming operation, it requires handling of harmful fumes and produces a solution containing hexavalent Cr, which is a hazardous substance. Elimination of the Cr removal step is a simplification of the fabrication process and therefore is a desirable act. We built two identical racetrack samples of the sintered joint and tested them in our joint test apparatus. One sample had Cr removed from the strands, the other had Cr intact. This paper provides a description of the test samples, fabrication steps, and results of the dc resistance measurements.

Synthesis and characterization of core–shell Ni/NiO nanoparticles/CuTl-1223 superconductor composites

Core-shell nickel/nickel-oxide (Ni/NiO) nanoparticles/Cu0.5Tl0.5Ba2Ca2Cu3O10−δ (CuTl-1223) superconductor composites were synthesized by solid-state reaction. The effect of these nanoparticles inclusion on structural and superconducting properties of CuTl-1223 matrix was investigated. Structural, morphological, and compositional properties were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) spectroscopy respectively. Superconducting transport properties were explored by dc-resistivity (ρ) measurements and the different oxygen vibrational modes of the composites were observed by Fourier transforms infrared (FTIR) spectroscopy. The variation of critical temperature (Tc) depends upon the nanoparticles contents in the host superconducting matrix. The overall suppression of Tc with increasing nanoparticles concentration is most probably due to trapping of mobile free carriers and pair-breaking caused by the reflection/scattering of carriers across these nanoparticles having net magnetic moment of metallic nickel in the core of nanoparticles.

Synthesis and characterization of nickel cobalt zinc ferrous hydrazine fumarate

Hydrazinated nickel cobalt zinc ferrous fumarate precursor has been synthesized and decomposed autocatalytically to Ni0.4Co0.2Zn0.4Fe2O4. The thermal decomposition behavior of the precursor has been investigated by thermogravimetric (TG) and differential thermal analysis (DTA). The chemical composition was assigned to precursor based on chemical analysis, TG–DTA, infrared (IR), isothermal mass loss, and total mass loss studies. The X-ray powder diffraction of the decomposed precursor confirms the formation of monophasic nickel cobalt zinc ferrite, and IR spectrum exhibits two peaks in the region of 340–420 and 550–660 cm−1 characteristic of spinel ferrites. The average grain size evaluated by TEM is found to be 15–20 nm. The electrical DC resistivity measurement was carried out with respect to temperature using two-probe method and dielectric properties as a function of frequency. The high dielectric constant values found at lower frequencies were due to nanosize nature of the “as prepared” ferrite. The Curie temperature of the “as-prepared” Ni0.4Co0.2Zn0.4Fe2O4 determined by alternating current susceptibility measurements was found to be 380 °C.

Suppression of activation energy and superconductivity by the addition of Al2O3 nanoparticles in CuTl-1223 matrix

Low anisotropic (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ (CuTl-1223) high Tc superconducting matrix was synthesized by solid-state reaction and Al2O3 nanoparticles were prepared separately by co-precipitation method. Al2O3 nanoparticles were added with different concentrations during the final sintering cycle of CuTl-1223 superconducting matrix to get the required (Al2O3)y/CuTl-1223, y = 0.0, 0.5, 0.7, 1.0, and 1.5 wt. %, composites. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy, energy dispersive X-ray, and dc-resistivity (ρ) measurements. The activation energy and superconductivity were suppressed with increasing concentration of Al2O3 nanoparticles in (CuTl-1223) matrix. The XRD analysis showed that the addition of Al2O3 nanoparticles did not affect the crystal structure of the parent CuTl-1223 superconducting phase. The suppression of activation energy and superconducting properties is most probably due to weak flux pinning in the samples. The possible reason of weak flux pinning is reduction of weak links and enhanced inter-grain coupling due to the presence of Al2O3 nanoparticles at the grain boundaries. The presence of Al2O3 nanoparticles at the grain boundaries possibly reduced the number of flux pinning centers, which were present in the form of weak links in the pure CuTl-1223 superconducting matrix. The increase in the values of inter-grain coupling (α) deduced from the fluctuation induced conductivity analysis with the increased concentration of Al2O3 nanoparticles is a theoretical evidence of improved inter-grain coupling.

Improvement of the critical current density in Bi-2223 ceramics by sodium–silver co-doping

Bi1.46Pb0.36Ag0.18Sr2Ca3Cu4−xNaxOy (x = 0, 0.05, 0.1 and 0.25) samples were prepared by a conventional solid state reaction method. The prepared samples are characterized using X-ray powder diffraction, scanning electron microscope, dc electrical resistivity and magnetic-hysteresis loop measurements. It has been shown that the Na doping in low contents significantly improves the physical properties of Bi-2223 phase. Magnetic hysteresis measurements have shown that the largest hysteresis curve belongs to Bi1.46Pb0.36Ag0.18Sr2Ca3Cu3.95Na0.05Oy sample including x = 0.05 Na content, indicating that it has best flux pinning capability in samples produced in this work. In addition, Jc values of the samples were calculated from the hysteresis loop measurement by using the Bean’s model showing that Jc increases with small amounts of sodium–silver co-doping.

Doping magnesium ion to tune electrical and dielectric properties of BaCo2 hexaferrites

Pure BaCo2 W-type hexaferrites i.e. BaCo2−xMgxFe16O27 (x≤1) have been synthesized by the chemical co-precipitation method at 1223K and have been investigated for their structural, electrical and dielectric properties. The X-ray diffraction (XRD) patterns conformed to the standard single phase of the hexagonal W-type structure. We examined the surface morphology of the prepared samples by the use of scanning electron microscopy (SEM) analysis. The dc-electrical resistivity (ρ) measurements showed metal to semiconductor transition (TM–S), in a temperature range of 298–663K. The maximum, at which the TM–S occurs, varies with the magnesium concentration in the samples. Crystallographic distribution of Mg2+ cations was responsible for the variation in the overall resistivity (ρ) pattern of BaCo2-W type hexaferrites. The dielectric constant (ε′) and the dielectric loss (tanδ) measurements at room temperature showed normal behavior of hexaferrites. The obtained results indicated that the Mg2+ ions played an important role in the tuning of the electric and the dielectric properties of BaCo2-W hexaferrites, which might have possible applications in transformer cores to reduce the eddy current losses.

Electrical, dielectric and magnetic characterization of Bi–Cr substituted M-type strontium hexaferrite nanomaterials

Strontium hexaferrite nanoparticles substituted with bismuth and chromium having nominal composition SrFe12−2xBixCrxO19 (x=0.2, 0.4, 0.6, 0.8) have been synthesized by the sol–gel method. The samples are characterized by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), DC electrical resistivity, magnetic and dielectric measurements. The XRD data shows that the nanoparticles are crystallized into single hexagonal magnetoplumbite phase. Room temperature DC electrical resistivity decreases on increasing the Bi–Cr contents. The dielectric constant, dielectric loss and tangent loss decrease with the frequency. The magnetic properties such as saturation magnetization (Ms), remanence (Mr) and coercivity (Hc) increase with increasing the dopant concentration up to x=0.2 and then decrease with further increase in dopant content. Coercivity decreases with increasing the dopant content up to x=0.2 then increases with further increase in dopant content. The increase in Ms and Mr while decrease in Hc indicates that the material with composition SrBi0.2Cr0.2Fe11.6O19 is suitable for magnetic recording media.