Dc Resistivity Measurements Research Articles

Conductance Model for Single-Crystalline/Compact Metal Oxide Gas-Sensing Layers in the Nondegenerate Limit: Example of Epitaxial SnO2(101).

Semiconducting metal oxide (SMOX)-based gas sensors are indispensable for safety and health applications, for example, explosive, toxic gas alarms, controls for intake into car cabins, and monitor for industrial processes. In the past, the sensor community has been studying polycrystalline materials as sensors where the porous and random microstructure of the SMOX does not allow a separation of the phenomena involved in the sensing process. This led to conduction models that can model and predict the behavior of the overall response, but they were not capable of giving fundamental information regarding the basic mechanisms taking place. The study of epitaxial layers is a definite improvement, allowing clarifying the different aspects and contributions of the sensing mechanisms. A detailed analytical model of the transduction function for n- and p-type single-crystalline/compact metal oxide gas sensors was developed that directly relates the conductance of the sample with changes in the surface electrostatic potential. Combined dc resistance and work function measurements were used in a compact SnO2(101) layer in operando conditions that allowed us to check the validity of our model in the region where Boltzmann approximation holds to determine the surface and bulk properties of the material.

Quasi Similar Routes of NO2 and NO Sensing by Nanocrystalline WO3: Evidence by In Situ DRIFT Spectroscopy.

Tungsten oxide is a renowned material for resistive type gas sensors with high sensitivity to nitrogen oxides. Most studies have been focused on sensing applications of WO3 for the detection of NO2 and a sensing mechanism has been established. However, less is known about NO sensing routes. There is disagreement on whether NO is detected as an oxidizing or reducing gas, due to the ambivalent redox behavior of nitric oxide. In this work, nanocrystalline WO3 with different particle size was synthesized by aqueous deposition of tungstic acid and heat treatment. A high sensitivity to NO2 and NO and low cross-sensitivities to interfering gases were established by DC-resistance measurements of WO3 sensors. Both nitrogen oxides were detected as the oxidizing gases. Sensor signals increased with the decrease of WO3 particle size and had similar dependence on temperature and humidity. By means of in situ infrared (DRIFT) spectroscopy similar interaction routes of NO2 and NO with the surface of tungsten oxide were unveiled. Analysis of the effect of reaction conditions on sensor signals and infrared spectra led to the conclusion that the interaction of WO3 surface with NO was independent of gas-phase oxidation to NO2.

Early Detection of Potential Induced Degradation by Measurement of the Forward DC Resistance in Crystalline PV Cells

Potential induced degradation (PID) is still a serious threat for the photovoltaic (PV) industry and it is expected to aggravate due to the tendency to increase the operating voltage of PV systems. Therefore, a method which can detect PID at an infant stage is necessary in order to increase the reliability of PV systems and preserve their lifetime. This paper provides a pathway (proof of concept) for the early and reliable detection of PID, by using the forward dc resistance (FDCR) of a PV cell since it is a parameter, which is affected by the cell's shunt resistance ( R sh), which in turn is heavily affected by PID before any significant power loss occurs, and could act as a PID detection mechanism. The paper presents simulation results, which examine at which forward bias conditions the FDCR has to be measured for the purpose of using it as a PID detection means at an early stage ( I 0), and ideality factor ( n ). Furthermore, an experiment was performed to verify the simulation results, demonstrating detection before 2% power loss occurs.

Dc electric conduction mechanisms and high frequency dielectric properties of different magnetoelectric composites

Various dc conduction mechanisms and high frequency (1MHz up to 3 GHz) dielectric properties have been studied for the particulate and 0-3 core shell composites. X -ray diffraction has been used to identify the structural properties. Tetragonal and cubic structures for PZT and ferrite respectively were appeared either in the pure form or in composites form. The microstructures have been investigated by TEM and particle size distribution was calculated. The microstructure plays a significant role in the electric properties. Dc resistivity vs. temperature measurements were implemented by using ‘two probe’ method. The room temperature resistivity was large in core shell in comparison with composite due to the unique microstructure of the core shell that enhances the interfacial disability of motion of carriers and increasing the carriers hopping path. Moreover, dc electric conduction mechanisms for all investigated samples have been determined. Curie temperatures for ferrimagnetic and ferroelectric phases were the transition points between the conduction mechanisms. Curie temperature of ferrites remarkably increased in the C.S. and composite. Finally, Dielectric and ac resistivity measurements were measured at room temperature. The dielectric constant (ε’) was enlarged in the core shell rather composite while the tangent loss was reduced. These appreciable enhancements could be useful in the high frequency applications.

Syntheses and physical properties of the MAX phase boride Nb2SB and the solid solutions Nb2SBxC1−x(x=0–1)

The MAX phase boride ${\mathrm{Nb}}_{2}\mathrm{SB}$ and the solid solutions $\mathrm{N}{\mathrm{b}}_{2}\mathrm{S}{\mathrm{B}}_{x}{\mathrm{C}}_{1\ensuremath{-}x}(x=0--1)$ were synthesized via solid-state methods and characterized by x-ray powder diffraction. All phases crystallize in the hexagonal ${\mathrm{Cr}}_{2}\mathrm{AlC}$ type with the space group $P{6}_{3}/mmc$. The lattice parameters increase with the boron content $[a=3.278(1)\ensuremath{-}3.334(1)\phantom{\rule{0.16em}{0ex}}\AA{}\phantom{\rule{0.16em}{0ex}}(+1.7%),\phantom{\rule{0.28em}{0ex}}c=11.49(1)\ensuremath{-}11.54(1)\phantom{\rule{0.16em}{0ex}}\AA{}\phantom{\rule{0.16em}{0ex}}(+0.5%)]$ and the distortions of the $\mathrm{N}{\mathrm{b}}_{6}(\mathrm{B},\mathrm{C})$ octahedra slightly decrease. Magnetic susceptibility and dc resistivity measurements confirm that ${\mathrm{Nb}}_{2}\mathrm{SC}$ is a superconductor while ${\mathrm{Nb}}_{2}\mathrm{SB}$ shows no superconducting transition above 1.9 K. The solid solutions $\mathrm{N}{\mathrm{b}}_{2}\mathrm{S}{\mathrm{B}}_{x}{\mathrm{C}}_{1\ensuremath{-}x}$ are metals and superconductors for $x=0--0.6$ with critical temperatures of ${T}_{\mathrm{c}}=4.8--2.6\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, which decrease with increasing boron content. First-principles density-functional theory calculations confirm the metallic state and a lower electronic density of states at the Fermi energy in the boride. The calculated elastic constants, phonon density of states, and Debye temperatures of ${\mathrm{Nb}}_{2}\mathrm{SB}$ are similar to ${\mathrm{Nb}}_{2}\mathrm{SC}$ and are probably not the reason for the absence of superconductivity in the boride. We therefore suggest that the lower $N({\ensuremath{\varepsilon}}_{\mathrm{F}})$ of the boride reduces the interaction strength and thus the superconducting critical temperature.

Polymer-assisted surface decoration for critical current enhancement in YBa2Cu3O7−x films

In this study, chemically decorated surfaces are employed as tools for Artificial Pinning Centres (APC) introduction in superconducting YBa2Cu3O7−x (YBCO) films. Self-assembled oxide nanostructures are grown on crystalline substrates via a very versatile and low-cost chemical technique called Polymer Assisted Deposition (PAD). Such decorated templates are used, in a second step, as substrates for YBCO film growth via Metal Organic Decomposition (MOD) or Pulsed Laser Deposition (PLD). The aim of the structures is to produce in the superconducting matrix strain and/or defects that should act as APCs and therefore enhance the transport properties of the samples. The oxides selected for the decoration are commonly used for the introduction of artificial pinning centres in YBCO: BaZrO3 and ZrO2. The decorated surfaces are analyzed via Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). YBCO films have been characterized via SEM, X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), DC resistivity and critical current measurements. The results show that the nanostructures are stable and that they can efficiently introduce strain and stacking faults in the film. This causes an increase in the value of the critical current density Jc and better in-field behaviour in all the investigated field range, compared to the analogous film grown on a standard substrate, especially for chemically derived YBCO. Also Jc angular dependence measurements, Jc(θ), show an isotropic enhancement of the critical current for every angle of application of the field.

Microfluidically synthesized Au, Pd and AuPd nanoparticles supported on SnO2 for gas sensing applications

Monometallic Au and Pd nanoparticles (NPs) and homogeneous AuPd nanoalloy particles were synthesized in a continuous flow of reactants (HAuCl4, K2PdCl4, NaBH4 and polyvinylpyrrolidone (PVP)) using a microfluidic reactor with efficient micromixers. The obtained ultrasmall NPs were subsequently deposited onto SnO2 supports with different surface area (32.7 and 3.6 m2 g−1). Samples with 1.0 and 0.1 wt.% metal loading were prepared. After calcination at 380 °C for 1 h the supported NPs aggregated to some extent. SnO2 supported AuPd nanoalloys with low (0.1 wt.%) metal loadings showed the smallest NP diameters (˜ 5–7 nm) and the narrowest size distribution among the samples. The gas sensing performance of the materials was investigated at 300 °C in four different gas atmospheres containing either CO, CH4, ethanol or toluene using dry and humid conditions. They exhibited a distinct variation in the response patterns and selectivity toward the test gases depending on composition and metal loading: Au increased the sensor signals compared to pristine SnO2 in all cases and decreased the interference of water vapor; the supported Pd NPs showed a weak response to toluene, strong sensitivity in CO sensing and slightly better response in ethanol sensing in humid air compared to dry air. However, they showed a high selectivity toward CH4 when used in dry air; AuPd alloy particles provided lower sensor signals compared to pristine SnO2 and no remarkable CH4 selectivity, in contrast to the Pd system. Operando diffuse reflectance infrared Fourier-transformed spectroscopy (DRIFTS) and DC-resistance measurements indicate a strong band bending in the case of Pd and AuPd NPs, whereas in the case of Au no band bending occured, indicating a strong electronic interaction between the support and Pd-containing NPs (Fermi-level control mechanism), and a weak electronic interaction between SnO2 and Au NPs (spill-over mechanism).

Conductive mechanism and the enhancement high-power electrical properties of Mn-modified Bi(Sc3/4In1/4)O3–PbTiO3–Pb(Mg1/3Nb2/3)O3 high temperature piezoelectric ceramics

In this research, we report the improved high-power electrical properties and the conductive mechanism of the 0.40Bi(Sc3/4In1/4)O3–0.58PbTiO3–0.02Pb(Mg1/3Nb2/3)O3–xMnO2 (BSI–PT–PMN–xMn, x = 0.0–0.8) system synthesized by a modified two-step solid state reaction method. A pure perovskite phase has been detected by the X-ray diffraction analysis of the BSI–PT–PMN–xMn ceramics, and the mechanical quality factor Qm has been found to increase from 28 to 210 with Mn content increasing from 0.0 to 0.8. The DC resistivity measurement indicated that the resistivity of the BSI–PT–PMN–xMn ceramics increases firstly, reaching the maximum at x = 0.4, and then decreases with more Mn modified. The conduction behavior can be described by the intrinsic charge carriers conduction mechanism and extrinsic semiconductor conductive mechanism in different temperature range. The high DC resistivity over 109 Ω cm at 300 °C together with the good electrical properties of piezoelectric constant d33 336 pC/N, planar electromechanical coupling factor kp 42.8%, mechanical quality factor Qm 120 and Curie temperature Tc 414 °C of the BSI–PT–PMN–0.4Mn ceramics makes it promising candidates for high temperature high-power piezoelectric applications.

New Er3+-substituted NiFe2O4 Nanoparticles and their Nano-heterostructures with Graphene for Visible Light-Driven Photo-catalysis and other Potential Applications

Background: Spinel ferrites have great scientific and technological significance because of their easy manufacturing, low cost and outstanding electrical and magnetic properties. Nickel ferrite nanoparticles are ferromagnetic material with an inverse spinel structure. They show remarkable magnetic properties and hence have a wide range of applications in magnetic storage devices, microwave devices, gas sensors, telecommunication, drug delivery, catalysis and magnetic resonance imaging. Objective: The aim and objective of this research article is to study the relative effect of NiErxFe2-xO4 nanoparticles and their composites with reduced graphene oxide (rGO) for the photocatalytic degradation reaction and other physical parameters. Method: Rare earth Er3+ substituted NiErxFe2-xO4 nanoparticles were synthesized via the facile wet chemical route. Six different compositions of NiErxFe2-xO4 with varied Er3+ contents such as (x) = 0.00, 0.005, 0.01, 0.015, 0.02 and 0.025 were selected for evaluation of the effect of Er3+ on various parameters of NiFe2O4 nanoparticles. Reduced graphene oxide (rGO) was prepared by Hummer’s method and was characterized by UV-Visible spectroscopy, X-ray powder diffraction and Raman spectroscopy. Nano-heterostructures of NiErxFe2-xO4 with rGO were prepared by the ultra-sonication method. Results: X-ray powder diffraction (XRD) confirmed the spinel cubic structure of all the compositions of NiErx- Fe2-xO4 nanoparticles. The photocatalytic degradation rate of methylene blue and congo red under visible light irradiation was found faster in the presence of NiErxFe2-xO4-rGO nanocomposites as compared to bare nanoparticles. It was also investigated that as the Er3+ contents were increased in NiErxFe2-xO4 nanoparticles, the dielectric parameters were largely affected. The room temperature DC-resistivity measurements showed that the Er3+ contents in NiFe2O4 are responsible for the increased electrical resistivity of ferrite particles. The electrochemical impedance spectroscopic (EIS) analysis of NiErxFe2-xO4 nanoparticles and NiErxFe2-xO4-rGO nanocomposites revealed that the ferrite particles possess low conductance as compared to the corresponding composites with graphene. Conclusion: The data obtained from all these characterization techniques suggested the potential applications of the NiErxFe2-xO4 nanoparticles and NiErxFe2-xO4-rGO nanocomposites for visible light driven photo-catalysis and high-frequency devices fabrication.

Evaluation of Superconducting Properties and Diffusion Behavior of Ex Situ and In Situ Bulk MgB2 Materials with Ni Coating

Ex situ and in situ bulk MgB2 superconducting materials have successfully been produced by the simple amorphous boron and nano-amorphous boron powders with the processes of ball milling, pressing, and annealing. The superconducting properties and diffusion behavior of MgB2 samples after nickel (Ni) coating process have been characterized and compared to the microstructure and performance of uncoated (bare) MgB2 bulk sample. One surface of MgB2 superconductor sample was coated with a thin Ni layer of about 50 − 60μm thickness using vapor deposition techniques in versatile high vacuum coater, then every sample was annealed at temperatures between 923 and 1123 K for 1 h. The role of annealing temperature on physical, electrical, superconducting, and structural characterizations of bare and Ni-coated ex situ/in situ MgB2 bulk superconductors has been studied using X-ray diffraction and dc electrical resistivity versus temperature measurements. Finally, the Ni diffusion coefficients (DNi = D0exp(E/kBT)) are calculated in the temperature range to calculate the required minimum activation energy value for the Ni atoms/ions into the ex situ MgB2 crystal structure for the first time.

Ferromagnetism in Cu2+ doped ZnO nanoparticles and their physical properties

Cu2+ doped ZnO nanoparticles designated as Zn1−xCuxO (x = 0.00, 0.02, 0.04, 0.06, 0.08 and 0.10) were prepared by sol–gel auto combustion technique. The modifications in structure, morphology, band gap, electrical, dielectric and magnetic properties due to Cu2+ doping were investigated through XRD, FE-SEM/EDAX, TEM/SAED, Raman, FT-IR, UV–Vis and VSM respectively. The analysis of XRD pattern reveals the incorporation of the dopants Cu2+ into ZnO lattice. The XRD spectra show that all the synthesized nanoparticles are a single crystalline phase with hexagonal wurtzite structure. The analysis of FE-SEM indicates that Cu2+ doping affects the surface morphology of ZnO. The compositional study performed by EDAX confirmed the presence of Zn, O, and Cu in stoichiometric proportion. TEM micrographs show the spherical shape of nanocrystals with small agglomeration. SAED patterns confirm the crystalline nature with hexagonal wurtzite structure. Raman spectra show the strongest peak at 437 cm−1 related to vibration of oxygen atoms in ZnO and also confirms optical phonon modes. FTIR result confirms the successful accompanying of Cu2+ ions into ZnO crystal lattice without changing its original structure. From DC electrical resistivity measurements it was found that electrical resistivity enhanced with increase in Cu2+ content. The measured dielectric parameters decreased with increase in Cu2+ content. An optical study revealed that the energy band gap decreased with doping of Cu2+ ions into ZnO nanoparticles. The VSM analysis shows the transformation of paramagnetic to superparamagnetic and superparamgnetic to ferromagnetic at room temperature due to Cu2+ doping in ZnO nanoparticles. The enhanced physical properties revealed that the prepared Cu2+ doped ZnO nanoparticles are the potential candidate for high-frequency devices, optoelectronic devices and spintronics devices application.

Enhancement in magnetic and electrical properties of Ni substituted Mg ferrite

Abstract In this work, Ni substituted magnesium spinel ferrites having general formula Mg1−xNixFe2O4 (where x = 0.0, 0.1, 0.15, 0.2, 0.25 and 0.3) were synthesized by standard solid state reaction method. All the samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM), DC resistivity measurements. X-ray diffraction analysis confirmed the single spinel phase. The lattice constant decreased with increasing Ni content due to the difference in the ionic radii of Mg2+ and Ni2+ ions. The FT-IR spectra reveled two prominent frequency bands in the wave number range of 400 cm−1 to 600 cm−1, which confirmed the cubic spinel structure of obtained compound and completion of chemical reaction. Magnetic studies revealed that the saturation magnetization increased with the substitution of Ni. The increase in magnetization was explained on the basis of distribution of magnetic and non-magnetic cations among A and B sites of the spinel lattice. A significant influence of cation distribution on DC electrical resistivity and activation energy was observed.

Impact of Ag-Doped on the Ferromagnetic-Metallic Transition in Pr0.75Na0.25mno3 Manganites

Monovalent doped Pr0.75Na0.25-yAgyMnO3 (y = 0–0.10) manganite have been investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM) as well as DC electrical resistivity and AC susceptibility measurement to clarify the influence of Ag- doped on charge ordering (CO) state. XRD analysis revealed all samples consists of essentially single phase and crystallized in an orthorhombic structure with space group Pnma. SEM images of Pr0.75Na0.25-yAgyMnO3 compound shows the successful substitution of Ag+ ions with the enhancement of the grains boundaries and sizes as well as the compaction of particles. On the other hand, resistivity and susceptibility measurements showed that the y = 0 sample exhibits insulating behavior and anti-ferromagnetic. Interestingly, the ferromagnetic-metallic transition was observed for y = 0.05 due to the revival of double-exchange (DE) mechanism as a result of weakening the Jahn-Teller effect which caused the CO state to be weakened. However, increasing of Ag-doped up to y = 0.10 induce back its transition into anti-ferromagnetic insulating behavior suggestively due to the weakening of DE mechanism.

Observation of Charge Ordering Signal in Monovalent Doped Nd0.75Na0.25-xKxMn1O3 (0 ≤ x ≤ 0.10) Manganites

K doping in the compound of Nd0.75Na0.25-xKxMn1O3 (x = 0, 0.05 and 0.10) manganites have been investigated to study its effect on crystalline phase and surface morphology as well as electrical transport and magnetic properties. The structure properties of the Nd0.75Na0.25-xKxMnO3 manganite have been characterized using X-ray diffraction measurement and it proved that the crystalline phase of samples were essentially single phased and indexed as orthorhombic structure with space group of Pnma. The morphological study from scanning electron microscope showed there was an improvement on the grains boundaries and sizes as well as the compactness with K doping suggestively due to the difference of ionic radius. On the other hand, DC electrical resistivity measurement showed all samples exhibit insulating behavior. However, analysis of dlnρ/dT-1 vs. T revealed the clearly peaks could be observed at temperature 210K for x = 0 and the peaks were shifted to the lower temperature around 190 K and 165 K for x = 0.05 and x = 0.1 respectively, indicate the existence of charge ordering (CO) state in the compound. Meanwhile, the investigation on magnetic behavior showed all samples exhibit transition from paramagnetic phase to anti-ferromagnetic phase with decreasing temperature and the TN was observed to shift to lower temperature suggestively due to weakening of CO state

Structural, transport and collosal dielectric properties of A-site substituted La2NiO4

A-site substituted nickelates of the type La2NiO4, La2-x Yx-y BayNiO4 (x = 0.1, y = 0.0, 0.05) prepared via solid state reaction route are reported. X-ray diffraction (XRD) data analysis confirms the type of phase and structure of synthesized samples. All the samples were found to have crystallized into the tetragonal structure (I4/mmm). The XRD results were further verified using Rietveld refinement technique and tetragonal structure with space group (I4/mmm) was confirmed for all the prepared samples under investigation. The single phased tetragonal lattice structure formation was also confirmed from Raman scattering spectroscopy via stretching modes of vibration displayed by the prepared nickelates around 440 cm−1 and 220 cm−1. The elemental composition was verified using EDAX technique while FESEM images revealed the porous nature and heavy agglomeration. The dielectric studies confirmed the collosal dielectric constant with lowered loss values in the frequency range of 105–106 Hz with retained dielectric constant in the range of 103–104 at 106 Hz. The low temperature four-probe dc resistivity measurement revealed the samples are semiconducting in nature.

Influence of Ba2+ on Opto-Electric Properties of Nanocrystalline BiFeO3 Multiferroic

The multiferroic compounds with chemical formula Bi1−xBaxFeO3 with x = 0.00, 0.05, 0.10, 0.15, 0.20, and 0.25 were synthesized by sol–gel route. Thermogravimetric and differential thermal analysis were performed on a pure BiFeO3 sample to know the required annealing temperature. Its structural, morphological, optical, electrical and dielectric properties were studied systematically by standard techniques. X-ray diffraction (XRD) and transmission electron microscopy techniques were employed to study the structure and phase, as well as the morphology of the samples respectively. The transition from the distorted rhombohedral perovskite (ABO3) to hexagonal crystal structure was revealed by XRD pattern with Ba2+ substitution having R3c space group. UV-visible absorption spectra show that the absorption edge shifts to lower wavelength with increasing Ba2+ concentration. DC electrical resistivity measurements revealed a linear decrease in resistivity carried out in the temperature range of 343–1073 K using a standard two probe method. The dielectric parameters such as dielectric constant (e′) and loss tangent (tanδ) were measured at room temperature in the frequency range 50 Hz–5 MHz, which was found to decrease with increasing frequency.

Improvement of superconducting parameters of Bi1.6Pb0.4Sr 2Ca 2Cu 3O10+ δ added with Au nanoparticles

Samples of Bi1.6Pb0.4Sr2Ca2Cu3O10+δ superconductor were prepared by solid-state reaction method to study the effects of gold nanoparticles addition to the superconducting system, Nano-Au was introduced by small weight percentages (0.25, 0.50, 0.75, 1.0, and 1.25 weight %). Phase identification and microstructuralcharacterization of the samples were investigated using XRD and SEM. Moreover, DC electrical resistivity as a function of the temperature, critical current density Jc, AC magnetic susceptibility, and DC magnetization measurements were carried to evaluate the relative performance of samples. x-ray diffraction analysis showed that both (Bi,Pb)-2223 and Bi-2212 phases coexist in the samples having an orthorhombic crystal structure. Both the onset critical temperatures Tc (onset) and zero electrical resistivity critical temperatures Tc (R=0) of the samples were determined from the DC electrical resistivity measurements. An improvement of the superconducting transition temperature of 6.36 % was obtained with increasing Au nanoparticles to x = 1.25 wt.%, while the critical current density is improved by 220 %. AC magnetic susceptibility measurement showed that the diamagnetic fraction and intergranular coupling of the x = 1.25 wt.% sample are greater than those of the others. The variation of magnetization with temperature (M-T curve) of the samples was measured by cooling the sample in zero fields (ZFC) and an applied field of 10 Oe (FC). The results of AC magnetic susceptibility and DC magnetization measurements were in good agreement with DC electrical resistivity measurement.

Frequency or Amplitude?-Rheo-Electrical Characterization of Carbon Nanoparticle Filled Epoxy Systems.

Dispersion of carbon nanoparticles in epoxy resin is the key factor to adjust the resulting electrical and mechanical properties of the nanocomposite. A profound understanding of the driving forces of standard methods like ultrasonic and mechanical dispersion is necessary. To derive the impact of applied frequency and strain on the resulting dispersion of multi-walled carbon nanotube (MWCNT)-filled epoxy resin, this work addresses the strain and frequency dependency of oscillatory shear flow-induced network changes. Strain- and frequency-sweeps were performed for a wide parameter set with in-line measurement of electrical DC resistance to monitor changes in the MWCNT network. Changes in electrical resistance reveal destruction and formation of the MWCNT network. A fundamental novel finding is the governing dependency of changes in the electrical network on applied shear amplitude. The applied frequency barely induces network changes. Applied shear rates do not correlate with particular network states.

Ytterbium doping effects on structural, optical and electrical properties of Bi4Ti3O12 system

Bi4-xYbxTi3O12 with x = 0.0, x = 0.1, x = 0.2 and x = 0.3 specimens were synthesized by conventional solid-state reaction. The influence of ytterbium doping on the structural, optical, dielectric and electrical properties of the synthesized compounds were investigated. The X-ray diffraction analysis showed that all samples are homogenous and crystallize in the orthorhombic system with the Fmmm space group. Also, it is found that the unit cell volume (V) goes on decreasing owing to the decrease of lattice parameters (a, b and c) with increasing Yb content. The absorbance measurement reveals that the intensity increases with increasing ytterbium concentrations. Also, it exhibits an additional peak occurred at the wavelength 975 nm. This peak has been attributed to the characteristic transitions from ground state 2F7/2 to excited states 2F5/2 of Yb3+ ions. From DC-resistivity measurements, it is noticed that all compositions exhibit a semiconductor behavior. In addition, it is found that below 420 K, the electrical resistivity was enhanced considerably upon substitution up to x = 0.3. Such behavior was attributed to the decrease of oxygen vacancies density. At 420 K, the parent compound exhibits a saturation region, which shifts to higher temperatures upon rising Yb content. The deduced activation energy values at high temperatures altercated around 990–828 meV. These values are attributed to oxygen vacancies migration. The electrical conductivity behavior of the samples was explained on the basis of jump relaxation model. As well the conductivity spectrum obeys to the Jonscher universal double power law.

Studies on structural, magnetic, and DC electrical resistivity properties of Co0.5M0.37Cu0.13Fe2O4 (M = Ni, Zn and Mg) ferrite nanoparticle systems

Ferrite nanoparticles of the composition Co0.5M0.37Cu0.13Fe2O4 (M = Ni, Zn, and Mg) have been synthesized using sol-gel auto combustion method. Structural properties are investigated using powder X-ray diffraction technique and the results showed a pure spinel crystal structures of the synthesized materials with lattice parameters in the range of 8.3331–8.4793 Å. Crystallite sizes are calculated using the Scherrer’s formula and the results are found to be in the range of 62.22–82.41 nm. The surface texture and morphological nature of the samples are studied by scanning electron microscopy which depicted clear crystalline nature of the materials. Characteristic vibrational states prevailing in the samples are studied using room temperature Fourier transform infrared spectroscopy. A two-probe DC electrical resistivity measurement of the samples showed a high resistive nature. Room temperature vibrating sample magnetometer measurements revealed the magnetic properties of the samples.