Dc Resistivity Measurements Research Articles

Enhancement of ferromagnetism by Cr doping in Ni-Mn-Cr-Sb Heusler alloys

A series of Mn rich Ni50Mn37−xCrxSb13 Heusler alloys have been investigated by dc magnetization and electrical resistivity measurements. Due to the weakening of the Ni-Mn hybridization, the martensitic transition shifts to lower temperatures with increasing Cr concentration, while the saturation magnetization at 5 K increases. The magnetoresistance and exchange bias properties are dramatically suppressed with increasing Cr concentration. The observed behaviors suggest that substitution of Cr for Mn in Ni50Mn37−xCrxSb13 Heusler alloys not only destabilizes the martensitic phase but also enhances ferromagnetism in the system. The possible mechanisms responsible for the observed behavior are discussed.

Effect of Er substitution on ultrasonic anomaly in Dy0.5−xErxBa0.5CoO3 cobaltates

Rare-earth cobaltates Dy0.5−xErxBa0.5CoO3 (x=0, 0.03 and 0.05) have been systematically investigated to elucidate the effect of Er substitution on elastic as well as magnetic and transport properties. DC electrical resistance and AC susceptibility measurements showed that the x=0 sample exhibited an insulating behavior and an anti-ferromagnetic (AFM) transition, TN at 198K as well as ferromagnetic (FM) transition, TC at 260K. Increasing of Er content suppressed the FM and AFM state suggestively due to the increase in size disorder arising from the size mismatch between A-site cations as shown from our calculation of variance σ2. On the other hand, both absolute longitudinal and shear velocities and related elastic moduli measured at 210K decreased with Er content in conjunction with the declining in the FM domain indicating a weakening in elastic properties. A longitudinal velocity anomaly characterized by a drop in velocity upon cooling before hardening with further cooling was observed for all samples. This abnormal elastic anomaly can be attributed due to the Jahn–Teller (JT) distortion of intermediate-spin Co3+ ions. Analysis of the elastic anomaly using the mean-field theory suggested that it is related to the JT effect which transformed from dynamic to static type with decreasing temperature. The elastic anomaly shifted to lower temperature from 129K (x=0) to 124K (x=0.05) with Er substitution indicating a weakening of the static JT effect.

Enhancement in superconducting transition temperature and Jc values in Na-doped Bi2Sr2Ca1Cu2−xNaxOy superconductors

The effects of Na substitution on the properties of Bi2Sr2Ca1Cu2−xNaxOy were investigated. The prepared samples are characterized using X-ray powder diffraction, scanning electron microscope, DC electrical resistivity and magnetic-hysteresis loop measurements. It has been found that with increasing Na doping for Cu, the transition temperature gradually increase while crystal lattice parameters slightly change. Magnetic hysteresis measurements have shown that the hysteresis loops of doped samples are greater than the undoped sample. In addition, significant enhancement has been observed in the Jc values of Na-doped samples, which were calculated from the M–H curves by using Bean’s critical state model.

Solder joint degradation and detection using RF impedance analysis

PurposeThe purpose of this paper is to clarify the method of using RF impedance changes as an early indicator of degradation of solder joint. It proposes the mode of crack propagation in solder joint and outlines why RF impedance analysis can be capable of detecting small cracks. The study aims to show the potential of RF impedance analysis as a prognostic tool that can provide advanced warning of impending failures of solder joint.Design/methodology/approachIn this paper, the mode of crack propagation in solder joint was studied to show why RF impedance analysis could be capable of detecting small cracks. A real simple impedance‐controlled test vehicle was developed to allow RF impedance and DC resistance measurements to monitor solder joint degradation. The influence of crack length on RF impedance was evaluated by high frequency structure simulator (HFSS) simulation for the first time.FindingsThe paper demonstrates that RF resistance can respond to an open state of a solder joint as well as DC resistance. Furthermore, RF impedance can monitor partial degradation of solder joints, while the DC resistance cannot do it. In addition, time‐domain reflection coefficient is found to be more useful than RF impedance in detecting solder joint degradation. The HFSS simulation results show that even very slight physical degradation of solder joints can be detected using RF impedance analysis.Originality/valueIn this paper, HFSS simulation is used for the first time to evaluate the influence of crack length on RF impedance.

Impact of Pt additives on the surface reactions between SnO2, water vapour, CO and H2; an operando investigation

The impact of Pt doping on the surface reactions between tin dioxide, water vapour, CO and H2 was investigated by a combination of simultaneously performed operando DRIFT (Diffuse Reflectance Infrared Fourier Transform) spectroscopy, DC resistance measurements and analysis of the reaction products by using a MS (Mass Spectrometer). Both undoped and Pt doped tin dioxide sensors were exposed to different test gases in synthetic air or in N2 backgrounds. The approach made it possible to identify the differences between the two materials with respect to their surface chemistry and their impact on the gas sensing performance. The main finding is that the presence of Pt changes the reaction partners' nature for water vapour and H2 on the one hand, and CO on the other hand when the sensors are operated in air. In this way the cross interference effect of humidity, which is responsible for the loss of CO sensing performance for the sensors based on undoped SnO2, is reversed.

Humidity Sensitive Characteristics of Porous Li-Mg-Ti-O-F Ceramic Materials

Ceramic porous MgTiO3 materials have been prepared by classical solid-state route. The sintered pellets of MgTiO3 with different LiF contents were characterized for humidity-sensing application. The sintered disks of these mixtures were subjected to capacitance measurements at 20℃as function of the relative humidity from which revealed that the Mixture MgTiO3 + 2% LiF (w/w) has the better characteristics. The disks were subjected to DC resistance measurements as a function of relative humidity in the range 15% - 95% RH. The selectivity of this material was discussed and compared to commercial sensor results. The response and recovery characteristics were assessed.

Structural, morphological, dielectrical, magnetic and impedance properties of Co1−xMnxFe2O4

The manganese (Mn) substituted cobalt ferrite (Co1−xMnxFe2O4) is synthesized by simple ceramic method with x varied from 0 to 0.5 in step of 0.1. The role of Mn substitution on structural, morphological, dielectrical, magnetic and impedance properties of cobalt ferrite has been investigated. Phase identification was performed by X-ray diffraction analysis which shows the spinel cubic crystal structure. The lattice parameter is found to increase with increase in Mn content. The saturation magnetization (Ms) and coercivity (Hc) are measured from hysteresis plots. Dielectric dispersion having Maxwell–Wagner-type interfacial polarization has been observed for cobalt ferrite samples. Dielectric constant and loss tangent are found to decrease with frequency. AC conductivity measurements suggest that the conduction is due to small polaron hopping. The semiconducting behavior of the samples has been studied by dc resistivity measurements. Room temperature complex impedance analysis shows semicircle attributed to the high resistance values at lower frequencies.

Study of Superconducting Properties in Bismuth-Based Cerium Doped High-T c Superconductors

Superconductivity in bismuth-based high-Tc superconducting materials attracts the researchers for their unique properties. Bismuth-based superconductors commonly called BSCCO have great importance among the superconducting family. These are divided into three phases among them 2223 phase is highly studied in order to investigate its superconducting properties by substitution of different elements. We have studied the substitution of cerium (Ce) on the calcium site of bismuth-based Bi(Pb)Sr(Ba)-2223 high-Tc superconductor. The nominal compositions of Bi1.6Pb0.4Sr1.6Ba0.4(Ca1−xCex)2Cu3Ox ceramic superconductor were prepared by the sol–gel method. X-ray diffraction (XRD) was done at room temperature for structural analysis and different parameters were calculated. Surface morphology was done by scanning electron microscopy (SEM). DC resistivity measurements for the transition temperature of synthesized superconducting samples were taken by the standard four-probe method, apparatus for which was developed in our laboratory. Current density measurements were also taken by the same apparatus. The synthesized superconducting samples were also characterized by thermogravimetric analysis (TG) and Fourier transformation infrared radiations (FTIR). It is observed that the substitution of cerium on the calcium site favors the formation of single high-Tc 2223 phase.

Effect of Substitution and Heat Treatment Route on Polycrystalline FeSe0.5Te0.5 Superconductors

The effect of atomic substitution of Te in iron based superconductors FeSe (1:1 type), which exhibits the simplest crystal structure among the iron-based superconductors, has been investigated in terms of structural, electronic transport, and magnetic properties. Polycrystalline samples with nominal Se:Te in FeSe1−x Te x samples for x=0.5350 °C, 0.5700 °C, 0.6700 °C, and 0.75700 °C were synthesized by the solid-state reaction method. In overall samples, it has been observed that the most superconducting properties seen in x=0.6700 °C samples, for 0.5350 °C and 0.5700 °C samples latter showed better superconducting properties as dc magnetic susceptibility, ac susceptibility, and resistivity measurements and sample homogeneity. T c enhancement is well correlated with the Te substitution up to 75 %.

A traceable technique to calibrate dc current shunts and resistors in the range from 10 μΩ to 10 mΩ

A traceable to dc resistance and dc voltage National Standards measurement technique to calibrate dc current shunts and resistors in the range from 10μΩ to 10mΩ has been developed at National Institute of Metrological Research (INRIM) in addition to the primary reference system for low value resistors calibration. This technique is applicable in secondary and industrial metrological laboratories. It is based on a volt-amperometric method, to compare an unknown shunt with a standard one in 1:1 or 1:10 ratios. In the setup are involved: a dc current calibrator and a current generator to supply currents respectively up to 100A and up to 1200A, with a switch to reverse the current, two 7 1/2 digit nanovoltmeters (nVs) for the acquisition of the voltage on the standard and under calibration shunts and two Tinsley 100μΩ and 1mΩ standard shunts kept in mineral oil and with a cooling system. An optional variation in the procedure that can reduce the measurement uncertainties is discussed. The 2σ relative capabilities of the technique span from 6.0×10−6to 4.6×10−4. Compatibility results with the INRIM reference measurement system for low value resistors calibration are also given.

Appearance of superconductivity in layered LaO0.5F0.5BiS2

Phase pure samples of LaOBiS2 and LaO0.5F0.5BiS2 are synthesized by conventional solid state reaction route via vacuum encapsulation technique at 800°C for 12h. Both the samples are crystallized in tetragonal P4/nmm space group with lattice parameters a=4.066(1)Å, c=13.862(4)Å for LaOBiS2; a=4.069(5)Å, c=13.366(2)Å for LaO0.5F0.5BiS2. Bulk superconductivity is confirmed in LaO0.5F0.5BiS2 with superconducting transition temperature (Tc) of 2.7K by DC magnetization and resistivity measurements. The isothermal magnetization (M–H) measurement shows closed loops with clear signatures of flux pinning and irreversible behavior. The magneto-transport ρ(T,H) measurements show resistive broadening and decrease in Tc (ρ=0) to the lower temperature with increasing magnetic field. The magnetic phase diagram involving upper critical and irreversibility fields as a function of temperature has been ascertained. The upper critical field Hc2(0) is estimated to be ∼19kOe corresponding to a Ginzburg–Landau coherence length of ∼130Å.

Influence of isothermal hot pressing-doping treatment on the electrical and mechanical properties of bulk Bi-Sr-Ca-Cu-O

The influences of (isothermal hot pressing-doping) treatment on the microstructure, electrical and mechanical properties of Bi2Sr3-xCaxCu2O8+δ (BSCCO), x ranging from 0.0 to 2 are assessed. BSCCO pellets were prepared by isothermal hot pressing (IHP) technique. The experimental works in this study consists of dc electrical resistivity measurements for electrical and superconducting properties, microhardness tests for mechanical characteristics, powder x-ray diffraction (XRD) for phase analyses (phase ratio), differential thermal analysis (DTA) for melting behaviour and scanning electron microscopy (SEM) for microstructure investigations. The results indicated that the Ca2+ doping and isothermal hot pressing increased significantly the superconducting transition temperature (Toc), which promotes the formation of high-Tc phase. Additionally, Vickers microhardness (VHN), Young's modulus, fracture toughness, brittleness index and elastic stiffness coefficient were also improved. Moreover, IHP-Doping improved the microstructure and the density of the BSCCO studied samples. Microhardness was found to be load dependent. Otherwise, we evaluated the load independent hardness, Young's modulus, fracture toughness and brittleness index of BSCCO samples. The possible reasons for the observed enhancement in electrical and mechanical properties due to (i) the homogeneity of grain region distribution (ii) the enhancement of superconducting phases.

Effect of Ce substitution on structural and superconducting properties of Bi-2212 system

In this study, Bi2Sr2Ca1−xCexCu2Oy, where x = 0, 0.01, 0.05, 0.1 and 0.25, superconducting samples were prepared by solid state method and subsequently used as feed in a laser induced directional solidification (LFZ) process. The physical properties of the samples were investigated by powder X-ray diffraction, scanning electron microscopy, dc-electrical resistance, magnetization, and magnetic-hysteresis loops measurements. It has been found that no significant difference has been observed in the critical transition temperatures of samples except for the sample with the highest Ce additions, which shows the lowest T C compared with the other doped samples. Magnetic hysteresis measurements have shown that the hysteresis loop is greater than the doped samples. In addition, critical current density values obtained from the hysteresis loops measurements by using Bean’s critical state model show a decrease with Ce-addition. All the results indicate that Cerium substitution for Ca produces the deterioration on the superconducting properties, compared with the undoped sample.

The role of Lu doping on microstructural and superconducting properties of Bi2Sr2CaLuxCu2Oy superconducting system

Lutetium (Lu) added Bi2Sr2CaLuxCu2Oy superconducting samples with x = 0, 0.1, 0.3, 0.5, 0.7 and 1.0 are prepared by solid-state reaction method and annealed at 840 °C for 50 h. The heating and cooling rates of the furnace are adjusted to be 10 and 3 °C/min, respectively. For the comparison, undoped sample is subjected to the same annealing conditions. The prepared samples are characterized using X-ray powder diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and dc resistivity (ρ−T) measurements. The volume fraction, grain size, texturing and lattice parameters are determined from the XRD measurements. The microstructure, surface morphology and element composition analysis of the samples produced are investigated by SEM and EDS measurements, respectively. Moreover, the resistivity (at room temperature), critical transition (onset and offset) temperature, variation of transition temperature and hole carrier concentration values of the samples studied are estimated from the dc resistivity measurements. According to the results obtained, the samples prepared exhibit the polycrystalline superconducting phase with less intensity of diffraction lines with the enhancement in the Lu addition due to the effect of the minor phase (Bi-2201). The lattice parameter c and volume fraction of Bi-2212 phase reduce systematically whereas the cell parameter a and minor phase fraction enhance with ascending the Lu content in the system, leading to the decrement in the superconducting properties. Scanning electron microscope measurements show that not only do the surface morphology and grain connectivity degrade but the grain sizes of the samples decrease with the increase of the Lu addition, as well. Energy dispersive spectroscopy results reveal that the Lu3+ ions might enter into the crystal structure by replacing Sr2+ ions, confirming why the superconducting properties of the pure sample are more superior to the samples doped. At the same time, dc resistivity results obtained show that the room temperature resistivity systematically increases with the enhancement of the Lu content as a result of the hole filling when the onset (T c onset ) and offset (T c offset ) temperatures determined from the resistivity curves decrease from 99.5 to 93.0 K and 85.0 to 60.0 K, respectively, illustrating not only the increment in the relative percentage of Bi-2201 phase formation and the reduction of the mobile carrier concentration but also the presence of impurities and weak links between the superconducting grains.

Investigation of microstructural, Vickers microhardness and superconducting properties of YBa2Cu3−xGdxO7−δ (0 ≤ x ≤ 0.150) superconducting ceramics via experimental and theoretical approaches

This study manifests the change of pinning mechanism, electrical, structural, physical, mechanical and superconducting properties of YBa2Cu3−xGdxO7−δ superconductors samples prepared by the conventional solid-state reaction method (x = 0, 0.025, 0.050, 0.100 and 0.150) by use of dc resistivity, X-ray analysis (XRD), scanning electron microscopy (SEM) and Vickers microhardness measurements. Zero resistivity transition temperatures (T ) of the samples are deduced from the dc resistivity measurements. Additionally, the lattice parameters are determined from XRD measurements when the microstructure, surface morphology and microhardness of the samples studied are examined by SEM and mechanical measurements, respectively. The results obtained demonstrate that T t values of the samples decrease slowly with the increase in the Gd content. The maximum T (92.0 K) is obtained for the pure sample prepared at 940 °C for 20 h in air atmosphere while the minimum value of 83.3 K is found for the sample doped with 0.150 Gd content. Moreover, it is obtained that J c values reduce from 132 to 34 A/cm2 with the enhancement of the Gd level in the crystalline structure. Further, the peak intensities belonging to Y123 (major) phase are obtained to decrease whereas the peak intensities of the minor phases such as BaCuO2 and Y211 are found to enhance systematically with the increment in the Gd content in the system, illustrating that partial substitution of Cu2+ ions by Gd3+ ions are carried out successfully. Moreover, SEM images display that the undoped sample obtains the best crystallinity and connectivity between superconducting grains and largest grain size whereas the worst surface morphology is observed for the maximum doped sample (x = 0.150). At the same time, Vickers microhardness, elastic modulus, load independent hardness, yield strength, fracture toughness and brittleness index values, playing important roles on the mechanical properties, are computed for all the samples. The experimental results of the microhardness measurements are examined using the Meyer’s law, PSR (proportional specimen resistance), modified PRS, Elastic–Plastic deformation model (EPD) and Hays–Kendall (HK) approach. The microhardness values obtained increase with the enhancement of the Gd content in the samples. Besides, it is noted that the Hays–Kendall approach is the most successful model explaining the mechanical properties of the samples studied in this work.

Crystallographic, magnetic and electrical properties of Ni0.5Cu0.25Zn0.25LaxFe2−xO4 nanoparticles fabricated by sol–gel method

The Ni0.5Cu0.25Zn0.25LaxFe2−xO4 (x=0.0, 0.25, 0.50, 0.75, 1.0) ferrite nanoparticles were fabricated by a sol–gel method. The crystallographic and magnetic properties of the powders were investigated by X-ray diffraction (XRD), transmission electron micrography (TEM), infrared spectroscopy (IR), vibrating sample magnetometer (VSM) and DC resistivity measurements. Phase identification of the samples was studied by the XRD patterns. XRD patterns shows the characteristics XRD peaks corresponding to the cubic spinel structure ferrites with the presence of secondary LaFeO3 phase. The lattice constant, porosity and specific surface area was increased whereas particle size, bulk density decreased with the increase in La3+ substitution. The TEM study reveals the fine particle nature of the ferrites with little agglomeration. The saturation magnetization (Ms) and coercivity (Hc) of the Ni–Cu–Zn samples were decreased with the La3+ substitution. DC resistivity indicates the semiconducting nature of the prepared samples. It has been found that the La3+ ions have a critical influence on the resultant structure, magnetic and resistivity properties of the Ni–Cu–Zn samples.

Improvements in electrical and dielectric properties of substituted multiferroic LaMnO3 based nanostructures synthesized by co-precipitation method

A series of La1−xGdxMn1−yCryO3 nanoparticles (where x, y=0, 0.25, 0.50, 0.75 and 1.0) has been synthesized by the chemical co-precipitation method, involving double ion substitution philosophy. The nanoparticles were characterized by thermo gravimetric analysis (TGA), X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, vibrating sample magnetometer (VSM), DC electrical resistivity and dielectric measurements. The XRD and FTIR analysis confirmed the single orthorhombic phase and the crystallite size were found in the range of 16–34nm. DC resistivity exhibited very interesting behavior which increased from 1.41×108 to 16.35±0.2×108Ωcm upon complete double ions replacement of La and Mn with Gd and Cr, respectively. This very high resistivity variation upon substitution definitely would open new avenues for applications of these materials in microwave devices and other related areas. The dielectric properties of these nanoparticles were also studied at room temperature in the range of 6kHz to 5MHz and the maximum dielectric behavior (ɛ′=2.86×103, tanδ=5.41, ɛ″=15.5×103) was exhibited by La0.75Gd0.25Mn0.75Cr0.25O3 at 6kHz. Hysteresis loops measurements showed that the synthesized nanomaterials are paramagnetic in nature at room temperature.

A newly designed Cu/Super-P composite for the improvement of low-temperature performances of graphite anodes for lithium-ion batteries

Copper nanoparticles supported on Super-P carbon (Cu/Super-P) are prepared by a one-pot microwave assisted procedure and used as conductive additive in graphite anodes for lithium-ion batteries. Anodes prepared with the Cu/Super-P additive show excellent cycling stability at temperatures as low as −30 °C with reversible capacities of the order of 180 mAh g−1. Four-points probe DC resistance measurements of layers prepared with Cu/Super-P demonstrate that the electronic resistance decreases of about half with respect to layers prepared with pristine Super-P. Additionally, the ac-impedance of Cu-modified electrodes is much lower than that of electrodes containing Super-P only. This implies an active role of the copper nanoparticles in improving the intercalation capacity, especially at low temperature.

Analysis of Indentation Size Effect on Mechanical Properties of Cu-Diffused Bulk MgB2 Superconductor Using Experimental and Different Theoretical Models

This study indicates the change of the electrical, microstructural, physical, mechanical and superconducting properties of Cu-diffused bulk MgB2 superconductors by means of scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), microhardness and dc resistivity measurements. The samples are prepared at different annealing temperatures in the range from 650 to 850 ∘C. Electrical and superconducting properties of samples are estimated from the dc electrical resistivity measurements. Moreover, microhardness measurements are performed to investigate the mechanical properties. Further, phase composition, grain sizes and lattice parameters are determined from the XRD measurements. At the same time, the surface morphology and grain connectivity of the samples are examined by SEM investigations. The measurements conducted demonstrate that both the Cu diffusion into the MgB2 system and the increment in the diffusion-annealing temperature increase the critical transition temperatures. Similarly, microstructure and grain size improve while the voids and porosity decrease with the increase of the diffusion-annealing temperature. In addition, the experimental results of the microhardness measurements are investigated using the Meyer’s law, PSR (proportional specimen resistance), modified PRS (MPSR), elastic-plastic deformation model (EPD) and Hays–Kendall (HK) approach. The obtained microhardness values of the samples decrease with the increase of the diffusion-annealing temperature up to 850 ∘C. The Hays–Kendall approach is found to be the most successful model describing the mechanical properties of the samples studied in this work.

Dielectric behavior and AC conductivity of Tb3+ doped Ni0.4Zn0.6Fe2O4 nanoparticles

Terbium doped Ni–Zn ferrite, Ni0.4Zn0.6TbxFe2−xO4 (x=0, 0.05, 0.1, 0.15 and 0.2) have been prepared through sol–gel technique. Formation of single phase FCC spinel structure is identified in all the compositions using X-ray diffraction technique. The effect of Tb3+ doping on the crystalline phase, crystallite size, dielectric properties and AC conductivity has been investigated in detail. Lattice constant is observed to increase with terbium content; but beyond certain concentration of terbium (x>0.15), it decreased. DC resistivity measurements were carried out in the temperature range 300–523K. All the compositions exhibited usual semiconducting nature of ferrites and the resistivity of the samples found to increase with terbium content up to x=0.15. The metallic behavior of the doped samples observed in the lower temperature region is explained in terms of elastic and inelastic scattering due to the rare earth ions. The investigations on dielectric constant, dielectric loss and AC conductivity was carried out in the frequency range 100Hz–20MHz from room temperature to 563K. Frequency dependence of dielectric constant showed normal behavior and is in good agreement with Koop’s phenomenological theory of dielectric dispersion. AC conductivity measurements suggested conduction due to small polaron hopping. AC conductivity as well as dielectric constant is found to increase with temperature and which is due to thermally enhanced drift mobility of charge carriers. The observed decrease in dielectric loss with terbium content up to x=0.15 is explained in terms of increase in resistivity.