Dc Resistivity Measurements Research Articles

The oxidizing effect of humidity on WO3 based sensors

Semiconducting metal oxide based gas sensors are used in a wide spectrum of fields, ranging from the detection of hazardous gases within the environment to monitoring air quality. WO3 is the second, after SnO2, most commonly used semiconducting metal oxide in commercial gas sensors. Despite its frequent application, the surface reactions responsible for sensing are largely unknown. Here, for the first time, a mechanism for the surface reaction between WO3 and humidity can be concluded from experimental results. DC resistance measurements and operando diffuse reflectance infrared Fourier transform spectroscopy show an oxidation of the WO3 lattice during humidity exposure. The filling of oxygen vacancies by water explains the effects atmospheric humidity has on WO3 based sensors, specifically the increase in resistance, the higher sensor signals to CO and the lower sensor signals to NO2. These findings are a basis for understanding how sensing occurs with WO3 based sensors.

The application of organic coatings in conservation of archaeological objects excavated from the sea

Protection of maritime cultural heritage is the mission of the National Maritime Museum (NMM) in Gdansk. This includes preservation of historical, cultural objects related to boat building, shipbuilding, sailing, military science, maritime education etc. Many archaeological objects, made from metal, wood and other organic materials and excavated from a wet environment, are kept at the NMM in Gdansk. In order to prevent the objects from any further degradation after the initial conservation process, different approaches are used including application of coatings, wax, paraffin wax and/or addition of different inhibitors. Due to various limitations (costs, human resources) conservators have been evaluating the performance of the coatings based on visible changes (corrosion signs) to decide when reapplication of the coating is necessary. In most cases the visible changes are indicators of coating damage and are non-reversible in character. Therefore there is a great need to find a method that will allow assessment of the performance of the coating in a relatively short time and efficient way. Electrochemical techniques such as measurement of DC resistance, Electrochemical Impedance Spectroscopy or Electrochemical Noise Measurement offer a way of achieving this. Each produces a number which is a measure of the ability of the particular coatings/inhibitor to protect effectively. In this paper the authors take as examples four coatings used to protect metal objects from particular shipwrecks found in Baltic area. Results are presented of some preliminary work conducted attempting to assess (rank) these four coatings on steel and copper using the DC resistance method. It is anticipated that this work will become one potential strand of a new development plan for better maintenance of archaeological objects.

Geophysical delineation of acidity and salinity in the Central Manitoba gold mine tailings pile, Manitoba, Canada

Surface electrical and electromagnetic geophysical methods can map enhanced electrical conductivity caused by acid mine drainage in mine tailings piles. In this case study, we investigate quantitative relationships between geophysical responses and the electrical conductivity, acidity and salinity of tailing samples at the Central Manitoba Mine tailings in Manitoba, Canada. Previous electromagnetic surveys at the site identified zones of enhanced conductivity that were hypothesized to be caused by acid mine drainage. In the present study, high-resolution EM31 and DC-resistivity measurements were made on a profile through a zone of enhanced conductivity and laboratory measurements of salinity and pH were made on saturation paste extracts from an array of tailing samples collected from the upper 2m of tailings along the profile.Observed spatial correlation of pH and pore-fluid salinity in the tailings samples confirms that the enhanced conductivity in the Central Manitoba Mine tailings is due to acid mine drainage. Contoured cross-sections of the data indicate that the acid mine drainage is concentrated near the base of the oxidized zone in the thicker parts of the tailings pile. The zone of increased acidity extends to the surface on sloping margins causing an increase in apparent conductivity in shallow penetrating geophysical responses. The quantitative relationship between measured pH and salinity shows that the conductivity increase associated with the acid mine drainage is due only in part to conduction by ions produced from dissociation of sulfuric acid. Comparison of the observations with fluid conductivity estimates based on statistical relationships of pH and ion concentrations in water samples from across the tailings pile shows that Ca2+ and Mg2+ ions also make significant contributions to the conductivity at all values of pH and Cu2+, Al3+ and Fe3+ ions make additional contributions at low pH. Variability in the measured conductivity at constant values of pH is explained by variations in the contribution of the SO42− to the measurements. The results of the study demonstrate the feasibility of using electromagnetic geophysical surveys to map acid mine drainage, and related ionic concentration, in mine tailings.

Modeling the Lifetime of Printed Silver Conductors in Cyclic Bending With the Coffin–Manson Relation

This paper discusses the modeling of the lifetime of printed conductors on a flexible substrate under cyclic bending. Roll-to-roll printed silver lines on a plastic film were exposed to cyclic strains accordant to the bending radii of 15, 20, and 30 mm, and their long-term electrical behavior was monitored in situ with four-point dc resistance measurements. By using 5%, 10%, and 20% increase in resistance as failure criteria, the lifetime of test populations was assessed utilizing the Weibull reliability analysis. Based on these results, the relationship between the applied strain and the lifetime was characterized and modeled by the Coffin–Manson equation. The Coffin–Manson relation accordant behavior for the lifetimes under various strains was also verified by confirming measurements with untapped bending radii with good results. As a conclusion, the lifetime of a printed conductor with known geometry and materials under cyclic bending was able to be modeled as a function of bending radius with the Coffin–Manson relation.

Performance Improvement of Pd/ZnO-NR/Si MIS Gas Sensor Device in Capacitive Mode: Correlation With Equivalent-Circuit Elements

Highly sensitive ethanol sensing performance of Pd/ZnO nanorods (NRs)/Si MIS device in the capacitive mode is reported in this paper. The MIS device with palladium as the top electrode and silicon as the substrate (bottom) employed ZnO-NRs as the semi-insulating sensing layer. The capacitive changes in the MIS device with exposure to ethanol vapor were measured as a function of temperatures, and 275 °C was found to be the temperature, where response is the fastest. In the capacitive mode, the response magnitude ( $\sim 7200$ % at 700-ppm ethanol) was found to be improved dramatically compared with that obtained by the conventional dc resistance measurement technique ( $\sim 45$ %). The underlying mechanism for such a significant improvement has been correlated with the corresponding change in the equivalent-circuit elements, considering the effective change in the dielectric constant of the sensing layer (consisting of ZnO-NR array, ZnO seed layer and voids) in air and in gaseous medium.

Electromagnetic Properties and Humidity-Sensing Studies of Magnetically Recoverable LaMg x Fe1−x O 3−δ Perovskites Nano-photocatalysts by Sol-Gel Route

Nanostructured perovskite mixed metal oxides, LaMg x Fe1−x O 3−δ (x= 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0), were synthesized successfully by a simple sol-gel route. The formation of single-phase perovskite oxides structure was confirmed by powder X-ray diffraction (XRD) analysis. The average crystallite size of the samples was evaluated using Sherrer’s formula. The presence of functional groups and metal oxide bonds was confirmed by Fourier transform infrared (FT-IR) analysis. Brunauer-Emmett-Teller (BET) surface adsorption studies showed better surface area of the compositions, which was further, evidenced by scanning electron microscopy (SEM) analysis. Room temperature vibrating sample magnetometer (VSM) analysis was confirmed that the superparamagnetic nature and the magnetization values decreased with increase in Mg-dopant. The samples were subjected to dc electrical conductivity studies at room temperature. The dc resistance measurements as a function of relative humidity (RH) at 5, 31, 51, 79, and 98 % were carried out on sintered discs at 25 ∘C under static conditions, which sensitivity factor S f (R 5% / R 95%) were calculated for LaMg x Fe1−x O 3−δ . The temperature-dependent conductance was also carried out in the range of 100–300 ∘C as suggested, and the activation energy was determined. Sample LaMgFe-4 (x= 0.6) possessed the highest humidity-sensing factor (12,926.03 ± 387), while LaFeO3 (x= 0) possessed the lowest sensitivity factor (41.66 ± 3). The response and recovery characteristics were studied for LaMgFe-4, which exhibited a very good narrow hysteresis loop. The photocatalytic degradation (PCD) of methylene blue (MB) dye was investigated under UV-visible light and the sample LaMgFe-4 showed better PCD efficiency than other samples, due to the smaller particle size and higher surface area.

Detection of DC currents and resistance measurements in longitudinal spin Seebeck effect experiments on Pt/YIG and Pt/NFO

In this work we investigated thin films of the ferrimagnetic insulators Y 3Fe5O12 and NiFe2O4 capped with thin Pt layers in terms of the longitudinal spin Seebeck effect (LSSE). The electric response detected in the Pt layer under an out-of-plane temperature gradient can be interpreted as a pure spin current converted into a charge current via the inverse spin Hall effect. Typically, the transverse voltage is the quantity investigated in LSSE measurements (in the range of μV). Here, we present the directly detected DC current (in the range of nA) as an alternative quantity. Furthermore, we investigate the resistance of the Pt layer in the LSSE configuration. We found an influence of the test current on the resistance. The typical shape of the LSSE curve varies for increasing test currents.

Structural, magnetic, and electrical features of the Nd2SrMn2TiO9 perovskite‐like compound

The synthesis process of the polycrystalline ceramic compound Nd2SrMn2TiO9 by means of the solid‐state reaction procedure is reported. The crystalline structure was analyzed through X‐ray diffraction experiments in the Bragg–Brentano recipe. The Rietveld refinement of the diffraction pattern by using the GSAS code shows that this material crystallizes in an orthorhombic structure, space group Pnma (#62), with lattice parameters a = 5.4764(6) Ǻ, b = 7.7468(6) Ǻ, and 5.4810(6) Ǻ. The surface morphology was studied by scanning electron microscopy images, which evidence the formation and compacting of grain with mean size 352.63 nm. Semiquantitative compositional analysis performed by means of Energy Dispersive X‐ray Spectroscopy shows the stoichiometric composition of the samples. Measurements of magnetization as a function of temperature reveal that this compound has a ferromagnetic behavior. The analysis with the Curie equation permitted to establish an effective magnetic moment μeff = 4.33 μB, which is 95.7% in agreement with the theoretical value expected from the Hund's rules. Measurements of DC resistivity as a function of temperature show a conductor behavior below the Curie temperature and insulator above. Evidences of a nonlinear response as a function of frequency with high values of relative dielectric constant reveal the occurrence of giant dielectric constant with ϵr = 6480 for ν = 100 Hz.

Analysis of electrochemical noise measurement on an organically coated metal

Electrochemical noise measurement (ENM) has found a credible place among the electrochemical methods applied to organic coatings, with a large number of reports in the literature of using the technique as a reliable method for the evaluation of the corrosion protection afforded by an organic coating on a metal surface. This has commonly been performed by calculating the noise resistance, Rn, or spectral noise resistance, Rsn, from the two main elements of electrochemical noise signal, the electrochemical current noise and potential noise. Several studies have shown that in practice Rn is a good measure of corrosion protection provided by an organic coating and affords good agreement with other measures of corrosion resistance from more established methods such as electrochemical impedance spectroscopy and DC resistance measurement. However, the theory of the electrochemical noise signal has not been fully analysed to elucidate the influence of the coating on the noise acquired. In this study a mathematical model is advanced in accordance with the equivalent electrical model in an electrochemical system consisting of a corroding metal substrate which has on it an organic coating. Experiments are also performed to evaluate the presented model in practice. Results of both theoretical and physical modelling show that potential noise is not influenced by the effect of coating while the current noise is attenuated due to the large impedance of coating.

Structural, optical and electrical characterization of nanocrystalline CdO films for device applications

Nanocrystalline CdO films were prepared onto glass substrate by employing an inexpensive, simple screen-printing method. Optimum conditions for preparing good quality screen-printed films were subsequently obtained. The grown films were characterized by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), scanning electron microscopy (SEM), UV–vis spectctroscopy and DC electrical resistivity measurement in vacuum by a two probe method. The XRD analysis reveals that the films were polycrystalline in nature, exhibiting cubic structure with preferential orientation of grains along (111) plane. EDAX analysis confirmed the presence of Cd and O element with some additional impurities. Scanning electron microscopy studies show that prepared films exhibited cauliflower like structures. Direct type of transition of band gap was confirmed by reflection spectra occurring at 2.5eV. The DC electrical resistivity measurement reveals that the films were semiconducting in nature with activation energy ∼0.270eV. Type of charge carriers of films were determined by Hall effect measurement.

Effect of Cr3+ substitution on electric and magnetic properties of cobalt ferrite nanoparticles

This work describes the effect of incorporation of Cr3+ into CoFe2O4 nanoparticles on its magnetic and electric properties, prepared by auto combustion method. The samples of CoFe2-xCrxO4 (x = 0, 0.15, 0.3) series were characterized by x-ray diffraction and field emission scanning electron microscopy to find out the average particle size. The substitution of Cr3+ caused a significant reduction in particle size of the modified systems. Room temperature Mossbauer spectroscopy and magnetic characterization were performed. Analysis of extracted parameters concluded that Cr3+ replaced the Fe3+ at B-site (octahedral). The decrease in magnetization at B-site was found responsible for the observed reduced saturation magnetization and coercivity. Impedance spectroscopic analysis has revealed the suppression of electrode-sample surface conduction effect and enhancement of material resistivity. The latter was confirmed by dc resistivity measurement. All these results were explained on the basis of occupancy of Cr3+ at B-site, surface anisotropy potential and reduced particle size.

Synthesis and Characterization of Ag Nanoparticles Addition on BPSCCO Superconducting Thin Films

The growth of epitaxial Ag nanoparticles doped (Bi, Pb)-2223 thin films on Si (111) substrates by pulsed laser deposition (PLD) and post-deposition oxygen annealing have been achieved. The phase identification and gross structural characteristics of synthesized films explored through X-ray diffractometer reveal that all the samples crystallize in orthorhombic structure. DC electrical resistivity measurements were done by the standard four-probe method and the results showed improvement in Tc by increasing Ag nanoparticles to 1.0 wt% which had a maximum enhancement in Tc for all investigated films. The surface morphology investigated through scanning electron microscope (SEM) and atomic force microscopy (AFM) results showed that an increase in Tc with the appropriate Ag nanoparticles addition in the samples is associated with the enhancement of Bi (Pb)-2223 phase formation.

UV-Light-Induced Fluctuation Enhanced Sensing by WO3-Based Gas Sensors

WO3-based gas sensors were investigated under UV-light irradiation and at different working temperatures with the object of achieving superior sensitivity and selectivity. Resistance fluctuations in the WO3 layer were studied together with dc resistance measurements. The data were taken in synthetic air, ethanol, nitrogen dioxide, and mixtures of these gases. We conclude that UV irradiation can easily be applied to enhance the gas sensing properties of a WO3 layer.

Static Electrode DC Resistivity Measurement at Surface Water for Pond Subsurface Layer Imaging

Resistivity methods in marine applications show slightly different processing techniques from land based resistivity surveys. Special DC resistivity instruments need to overcome difficulties in arranging the electrode with straight array lines and position. Some geoelectrical instrument manufacturers developed equipment which is able to measure resistivity values and positions in real time. In this paper we demonstrate an application of ordinary geoelectrical instruments for resistivity acquisition in water environment. This study is motivated by the inability to apply conventional DC resistivity instruments in water environment. Land resistivity survey array is arranged on the surface of water using static electrode mode. The method has been tested in various environments, such as ponds/lakes with quiet until rough waves and also measurements at coastal environments. Measurement at the ponds/lakes water environment resulted in data that are almost identic to the measurements obtained using standard land DC resistivity method. On the other hand the measurement in coastal environment does not work properly, possibly due to the lack of power source.

Development of CoFe2O4 thin films for nitrogen dioxide sensing at moderate operating temperature

Cobalt ferrite thin films were deposited onto quartz substrates by spray pyrolysis technique and their gas sensing properties were investigated. X-ray diffraction study confirms that films are polycrystalline in nature and exhibit single phase spinel cubic crystal structure. DC electrical resistivity measurement indicates the semiconducting nature of the films. The surface morphology study confirms the formation of grains structure with grain size about 200–400 nm. Room temperature variation of dielectric properties with frequency suggests the normal dielectric performance of the cobalt ferrite thin film. The influence of quantities of spraying solutions on the operating temperature, sensitivity and selectivity, gas concentrations, response and recovery characteristics of gas sensor are systematically tested. The maximum gas response 95% was observed for film prepared at 50 mL quantity of solution for 80 ppm NO2. The films are extremely selective towards NO2 as compared to other target gases. Gas response attains nearly 90% of its initial value after 90 days indicates good durability of the films.

Decrement in metastability with Zr nanoparticles inserted in Bi-2223 superconducting system and working principle of hybridization mechanism

This exhaustive study experimentally deals with the role of Zr foreign impurities on the electrical, superconducting and flux pinning properties of the bulk Bi-2223 superconducting compounds by the typical experimental characterization methods such as dc resistivity (ρ–T), transport critical current density (J c ) and powder X-ray diffraction (XRD) surveys. All the experimental findings show that the curial characteristics, being in charge of the varied attractive and feasible applications, retrograde significantly with the enhancement of the Zr nanoparticles in the Bi-2223 superconducting system due to the presence of two trap levels for mobile holes. This leads to the degradation of the metastability of the superconducting materials. In more detail, based on the dc resistivity and transport critical current density measurements, the Zr additives give rise to the localization problem as a consequence of the change in the dynamics of electron–electron interaction. Thus, the room state conductivity, $$T_{c}^{onset}$$ , $$T_{c}^{offset}$$ and J c values retrograde significantly. Similarly, the Zr foreign impurities embedded in the Bi-2223 crystal lattice make the artificial random defects, dislocations and grain boundary weak-interactions in the consecutively stacked layers enhance immediately, and the superconducting Cu–O2 layers distort especially. Moreover, the XRD investigations including the evidences about the decrement/increment in the c-axis/a-axis length verify the regression of the superconducting properties with the Zr dopant. The main differentiation of the lattice constant parameters stems from aliovalent substitutions (replacement of the divalent Cu by the tetravalent Zr impurties) along with the crystal structure. In other words, the reduction of the electronegativity leads to decrease the mobile hole concentration in the Cu–O2 consecutively stacked layers. Furthermore, all the decrement parameters are theoretically favored by hybridization mechanism.

Synthesis, characterization and electrical properties of novel Mn substituted MgAl2O4 synthesized by sol–gel method

Nanostructured manganese doped magnesium aluminate (Mg1−xMnxAl2O4, where x = 0.0, 0.25, 0.50, 0.75, 1.0) were prepared by a sol–gel method. All the samples were characterised by TGA, XRD, SEM, EDAX, TEM and IR spectroscopy techniques. The semiconducting nature of materials were investigated by DC resistivity measurement. The TGA curves show that spinel the oxides are formed at 600 °C. The XRD studies reveal formation of cubic spinel phase with average crystallite size of 28 nm. The composition of Mg1−xMnxAl2O4, (x = 0.0, 0.50, 1.0) shows spherical interlinked fibrous morphology. The elemental compositions determined by energy dispersive X-ray analysis (EDAX) indicate desired composition. Particle size obtained from TEM analysis was found to be ~23 nm. The IR spectra show two strong characteristic absorption bands at tetrahedral and octahedral sites. The temperature dependent variation of dc resistivity of material reflects semiconducting nature of materials.

Energy exchange between phononic and electronic subsystems governing the nonlinear conduction inDCNQI2Cu

We present a dynamical study on the nonlinear conduction behavior in the commensurate charge-density-wave phase of the quasi-one-dimensional conductor ${\mathrm{DCNQI}}_{2}\mathrm{Cu}$ below 75 K. We can accurately simulate magnitude and time dependence of the measured conductivity in response to large voltage pulses by accounting for the energy exchange between the phononic and electronic subsystems by means of an electrothermal model. Our simulations reveal a distinct nonequilibrium population of optical phonon states with an average energy of $\overline{{E}_{\text{ph}}}=19$ meV, being half the activation energy of about $\mathrm{\ensuremath{\Delta}}{E}_{a}=39$ meV observed in dc resistivity measurements. By inelastic scattering, this hot optical phonon bath generates additional charge-carrying excitations, thus providing a multiplication effect while energy transferred to the acoustic phonons is dissipated out of the system via heat conduction. Therefore, in high electric fields a preferred interaction of charge-carrying excitations with optical phonons compared to acoustic phonon modes is considered to be responsible for the nonlinear conduction effects observed in ${\mathrm{DCNQI}}_{2}\mathrm{Cu}$.

Study of microstructure and augmentation of DC electrical resistivity due to Al3+ substitution in Ni–Zn nano ferrite system synthesized via auto combustion

Nanocrystalline Ni–Zn–Al spinel ferrite was synthesized via citrate-gel auto combustion method. The as-prepared powders have been separated into two batches in which one batch of powders were sintered at 1000[Formula: see text]C for 4 h and the other batch were pressed into pellets and were sintered at the same temperature. Sintering of the samples was done in air atmosphere followed by natural cooling to room temperature. The heat treated powders have then been characterized using TG–DTA, XRD, SEM and TEM for thermal, structural and microstructural aspects while the DC electrical resistivity measurements were carried out on the sintered pellets. The X-ray diffraction patterns displayed the formation of the spinel phase for all powders and the lattice parameter was obtained using Bragg’s law. The crystallite size for all compositions were found to be in nano dimensions and obtained from the Williamson–Hall method. TG–DTA analysis of the undoped [Formula: see text] indicated the formation of the spinel phase is around 400[Formula: see text]C while almost uniform microstructure with a more or less spherical grains has been noticed in the SEM micrograph. An enhancement in the DC electrical resistivity ([Formula: see text]-cm) has been observed in [Formula: see text] synthesized using this technique in comparison with that processed through conventional ceramic technique and a modification in the resistivity has been observed on substituting [Formula: see text] in place of [Formula: see text]. High electrical resistivity makes these ferrites suitable for high-frequency applications due to possible reduction of the eddy current losses. The observed variation in resistivity has been discussed on amendments in structure, microstructure and unavailability of [Formula: see text] ions with increasing [Formula: see text] ions in the light of existing understanding. The decrease in resistivity with increasing temperature confirms the semiconducting behavior of all samples. Activation energies for conduction were obtained from the slope of the log [Formula: see text] versus [Formula: see text] plots and observed to be in the range of 0.6–0.45 eV. The variation in the activation energy for conduction followed a similar trend as the DC resistivity. The drift mobility decreases with increasing [Formula: see text] ions concentration and increases with increasing temperature.

Cyclic Bending Reliability of Silk Screen Printed Silver Traces on Plastic and Paper Substrates

The effect of the substrate on the cyclic bending reliability of screen printed silver traces is studied in this paper. The silver screen printed test samples in this study were three different plastic films and three varieties of paper sheets. The specimens with line widths of 250, 500, 1000, and 2000 $\mu\mbox{m}$ were subjected to cyclic bending, and their electrical behavior was monitored with dc resistance measurements in situ . In this study, a 20% increase in resistance was defined as the failure criterion, and the reliability of each test population was assessed by a statistical Weibull analysis. The results showed that the reliability of the traces was highly dependent on the substrate thickness in all the studied materials. The traces on a 125- $\mu\mbox{m}$ -thick polyethylene terephthalate substrate were found to have the lowest characteristic lifetimes of about 1000 bending cycles, whereas the traces with the same geometry on polyethylene terephthalate with a thickness of 50 $\mu\mbox{m}$ endured hundreds of thousands of bending cycles. Similarly, decreasing the substrate thickness improved the reliability of the printed traces on paper substrates. This relationship was due to the reduced mechanical strain on the trace surface when using thinner substrates.