Drop In Electrical Conductivity Research Articles

Thermoelectric properties of A-site deficient reduced Sr0.775La0.15-xEuxTiO3-δ (0 ≤ x ≤ 0.15)

There are numerous different schemes to improve the figure of merit (ZT) in oxide thermoelectrics, including creating additional electrons using oxygen vacancies, chemical doping, and A-site nonstoichiometry. A-site deficient (Sr,La)0.925TiO3- δ has shown promise as an n-type oxide thermoelectric; herein, additional A-site substitutional doping with Eu was used to improve ZT, through a combination of A-site size mismatch and non-stoichiometry. A solid solution series Sr0.775La0.15-xEuxTiO3-δ (0 ≤ x ≤ 0.15) was synthesised, showing a modest improvement in thermoelectric properties for x = 0.05, with a ZT of 0.18 at 600 °C, vs a ZT of 0.16 in the end member composition. Upon full characterisation, the additional electrons provided by the formation of oxygen vacancies were being used up by reduction of the added europium dopants, leading to a drop in electrical conductivity, and correspondingly, ZT. This gives a useful perspective in choosing dopants for schemes such as these.

Native Defects Hybridization and Electronic Transport in Cu2Se‐CuGaSe2 Hierarchical Composites

AbstractEngineering the energy distribution of electronic defects in semiconductors can afford the coexistence of degenerate and nondegenerate transport behavior. By leveraging native defects in Cu2Se and CuGaSe2 phases, the tunability of the concentration and energy distribution of active electronic defects in hierarchical (1‐x)Cu2Se‐(x)CuGaSe2 composites is demonstrated. This study found that the electrical conductivity of various composites decreases with rising temperature indicating degenerate semiconducting behavior, whereas the carrier density increases with temperature, which is consistent with non‐degenerate semiconductivity. Remarkably, this study found that while the carrier density and electrical conductivity drop with the increasing CuGaSe2 content for samples with x ≤ 0.45 is consistent with an increase in the activation energy of “active” electronic defects, the sudden increase by 140% in the electrical conductivity and by 109% in the carrier density for near equimolar composition suggests the formation of a large density of electronic defects with lower activation energy. This unusual behavior is understood within the context of the hybridization of coexisting native electronic defects to form degenerate hybrid acceptor states with lower activation energy. The reported unique electronic transport can be leveraged for the development of more versatile electronic and optoelectronic devices with superior performance.

High-Performance PEEK/MWCNT Nanocomposites: Combining Enhanced Electrical Conductivity and Nanotube Dispersion.

High-performance engineering thermoplastics offer lightweight and excellent mechanical performance in a wide temperature range. Their composites with carbon nanotubes are expected to enhance mechanical performance, while providing thermal and electrical conductivity. These are interesting attributes that may endow additional functionalities to the nanocomposites. The present work investigates the optimal conditions to prepare polyether ether ketone (PEEK)/multi-walled carbon nanotube (MWCNT) nanocomposites, minimizing the MWCNT agglomerate size while maximizing the nanocomposite electrical conductivity. The aim is to achieve PEEK/MWCNT nanocomposites that are suitable for melt-spinning of electrically conductive multifilament's. Nanocomposites were prepared with compositions ranging from 0.5 to 7 wt.% MWCNT, showing an electrical percolation threshold between 1 and 2 wt.% MWCNT (107-102 S/cm) and a rheological percolation in the same range (1 to 2 wt.% MWCNT), confirming the formation of an MWCNT network in the nanocomposite. Considering the large drop in electrical conductivity typically observed during melt-spinning and the drawing of filaments, the composition PEEK/5 wt.% MWCNT was selected for further investigation. The effect of the melt extrusion parameters, namely screw speed, temperature, and throughput, was studied by evaluating the morphology of MWCNT agglomerates, the nanocomposite rheology, and electrical properties. It was observed that the combination of the higher values of screw speed and temperature profile leads to the smaller number of MWCNT agglomerates with smaller size, albeit at a slightly lower electrical conductivity. Generally, all processing conditions tested yielded nanocomposites with electrical conductivity in the range of 0.50-0.85 S/cm. The nanocomposite processed at higher temperature and screw speed presented the lowest value of elastic modulus, perhaps owing to higher matrix degradation and lower connectivity between the agglomerates. From all the process parameters studied, the screw speed was identified to have the higher impact on nanocomposite properties.

Optimizing nanofluid additives for enhanced thermophysical properties in anionic crude oil for EOR applications

AbstractThis research delved into the effects of introducing multi‐walled carbon nanotubes (MWCNTs) and sodium dodecyl sulphate (SDS) into crude oil with an anionic base, aiming to enhance its thermophysical attributes in the EOR process. The investigation encompassed a range of properties, including interfacial tension, viscosity, density, and electrical conductivity, measured using an LV rheometer with spindle 18. Various ratios of MWCNTs and SDS were mixed with the crude oil to evaluate their impacts. The study uncovered that the 1:1 ratio of MWCNTs to SDS achieved a noteworthy 10% reduction in interfacial tension while minimally affecting viscosity, showing promise for practical applications. Temperature had diverse effects on viscosity and interfacial tension, displaying fluctuating trends. The highest observed result was a substantial 190% viscosity increase at 40°C with a 2:1 ratio, whereas the lowest was a slight −0.81% density change at 60°C for the 1:1 ratio. Additionally, interfacial tension consistently decreased over time for all ratios at various temperatures, with the most significant reductions observed at 40 and 60°C, particularly for the 1:2 and 1:1 ratios. Furthermore, adding MWCNTs and SDS led to a remarkable drop in electrical conductivity, indicating a substantial decrease in salt content within the crude oil. However, it was noted that higher MWCNT concentrations might not be cost‐effective, emphasizing the importance of optimizing additive ratios for a balance between performance and economic viability. This study highlights the potential of tailored nanofluid formulations to improve the thermophysical properties of crude oil, potentially enhancing extraction and refining processes.

Simulation of two nanoparticle melting to understand the conductivity drop of 3D-printed silver nanowires

The future flexible sensor technology will require low-temperature, fast processing 3D printing techniques that will rely heavily on the quality of nanoparticle (NP) Ink. Electrical conductivity has been found to decrease in majority of the 3D printed electronic wires. Herein we report a fundamental understanding in drop of electrical conductivity in processed silver (Ag) line wire, generally found in Ag-nanoparticle Ink, using large-scale atomistic molecular dynamics (MD) simulations of sintering of five different sizes of Ag NPs. To preserve the high conductivity of pure silver wires, the integrity of the pristine face-centered cubic (FCC) crystalline structure must be retained in the processed line wires. Simulations show that the pristine Ag FCC structures of the nanoparticles are not recovered after melting and resolidification, instead, the resolidified material is paracrystaline. The breakdown of pristine FCC structures might be the cause of the drop in conductivity of processed Ag wires. Simulation results suggest that the intermediate size nanoparticles retain highest percentage of the pristine silver face-centered cubic (FCC) structure after pulse treatments. Our results show that the most promising Ag-Ink should contain smaller to medium size silver NPs that can retain FCC structure after 3D printing of the Ag-Ink.

Synthesis and Characterization of Tb–Er Co–Doped Bi2O3 Solid Electrolyte Systems

In this study, solid state reactions were used to create Er–Tb co–doped Bi2O3 solid electrolyte systems. Four Point Tip Technique (FPPT), Thermo–gravimetric and Differential Thermal Analysis (TG & DTA), and X–Ray Diffraction (XRD) were used to characterize the generated samples' structural and thermal properties, and electrical conductivity. The samples 05Er05TbSB, 05Er10TbSB, and 15Er05TbSB stabilized with cubic δ–phase at room temperature, according to XRD data. Due to the smaller dopants ions compared to the host Bi3+ cation, the lattice constants estimated for these samples were lower than those of the pure cubic phase. The samples were thought to be thermally stable in the studied temperature range since the thermal curves did not show endothermic or exothermic peak development indicating a potential phase change. According to the Arrhenius equation, the temperature–dependent conductivity graphs displayed a linear change. The conductivity measurements clearly indicated that an increase in doping rate results in a sudden drop in electrical conductivity. The calculated activation energies increased with the doping ratio and varied from 0.64 eV to 1.12 eV. At 700 °C, it was determined to be 0.128 S.cm–1 for the sample 05Er05TbSB, which had the greatest conductivity and lowest activation energy among all samples. The conductivity was discovered to decrease and activation energy to increase when the doping ratio was gradually raised.

Engineering of Thermoelectric Composites Based on Silver Selenide in Aqueous Solution and Ambient Temperature.

The direct, solid state, and reversible conversion between heat and electricity using thermoelectric devices finds numerous potential uses, especially around room temperature. However, the relatively high material processing cost limits their real applications. Silver selenide (Ag2Se) is one of the very few n-type thermoelectric (TE) materials for room-temperature applications. Herein, we report a room temperature, fast, and aqueous-phase synthesis approach to produce Ag2Se, which can be extended to other metal chalcogenides. These materials reach TE figures of merit (zT) of up to 0.76 at 380 K. To improve these values, bismuth sulfide (Bi2S3) particles also prepared in an aqueous solution are incorporated into the Ag2Se matrix. In this way, a series of Ag2Se/Bi2S3 composites with Bi2S3 wt % of 0.5, 1.0, and 1.5 are prepared by solution blending and hot-press sintering. The presence of Bi2S3 significantly improves the Seebeck coefficient and power factor while at the same time decreasing the thermal conductivity with no apparent drop in electrical conductivity. Thus, a maximum zT value of 0.96 is achieved in the composites with 1.0 wt % Bi2S3 at 370 K. Furthermore, a high average zT value (zTave) of 0.93 in the 300-390 K range is demonstrated.

Evolution of electrical conductivity in semi‐interpenetrating polymer network of shape memory polyvinyl chloride and polyaniline

AbstractElectrically conductive semi‐interpenetrating polymer network (IPN) from shape memory polyvinyl chloride (PVC) and polyaniline (PANI) is realized. The mechanical properties and shape memory performance of semi‐IPN are slightly different from the original PVC. The distribution of PANI within PVC is found to be non‐uniform in the thickness direction. The electrical conductivity of the as‐fabricated sample at room temperature is around 4.5 × 10−2 S/cm. However, after heating, thermal strain results in significant drop in electrical conductivity. Programming remarkably reduces the electrical conductivity as well. A higher programming temperature and higher programming strain result in more reduction. Subsequent heating for shape recovery causes further reduction in electrical conductivity, despite nearly full shape recovery is achieved. Doping (dedoping and redoping) is confirmed not the major player, but microgaps/fracture in PANI chains during stretching in programming and heating for shape recovery.

On the Origin of Seebeck Coefficient Inversion in Highly Doped Conducting Polymers

AbstractA common way of determining the majority charge carriers of pristine and doped semiconducting polymers is to measure the sign of the Seebeck coefficient. However, a polarity change of the Seebeck coefficient has recently been observed to occur in highly doped polymers. Here, it is shown that the Seebeck coefficient inversion is the result of the density of states filling and opening of a hard Coulomb gap around the Fermi energy at high doping levels. Electrochemical n‐doping is used to induce high carrier density (>1 charge/monomer) in the model system poly(benzimidazobenzophenanthroline) (BBL). By combining conductivity and Seebeck coefficient measurements with in situ electron paramagnetic resonance, UV–vis–NIR, Raman spectroelectrochemistry, density functional theory calculations, and kinetic Monte Carlo simulations, the formation of multiply charged species and the opening of a hard Coulomb gap in the density of states, which is responsible for the Seebeck coefficient inversion and drop in electrical conductivity, are uncovered. The findings provide a simple picture that clarifies the roles of energetic disorder and Coulomb interactions in highly doped polymers and have implications for the molecular design of next‐generation conjugated polymers.

Surfactant-assisted water-based graphene conductive inks for flexible electronic applications

BackgroundInkjet printing of graphene conductive inks plays a critical role in the technological advancement in flexible and stretchable electronics applications. In this study, water-based graphene conductive ink was fabricated and printed through inkjet printing on polyethylene terephthalate substrate. MethodsDeionized (DI) water and three different types of surfactants (sodium dodecyl sulfate (SDS), polyvinylpyrrolidone (PVP), and Gum Arabic GA)) were utilized in the preparation of graphene conductive inks. Significant FindingAmong other conductive ink formulations, graphene conductive inks fabricated using the DI/PVP surfactant exhibit relatively higher wetting and stability properties. In addition, this formulation led to an increment of about 80% in electrical conductivity compared to DI water-based conductive ink. The results revealed an improvement of about 50 times in the electrical conductivity of the printed film when the number of the printing cycle was increased from 1 to 10. Furthermore, it was observed that under 50% tensile strain, the graphene film prepared using the PVP surfactant exhibited only a 0.12% drop in electrical conductivity. Therefore, it is inferred that the conductive inks prepared from DI/PVP surfactants are highly suitable for use in flexible and wearable electronics.

Role of calcination on geopolymerization of lateritic clay by alkali treatment

In the present study, the role of calcination of a low iron lateritic clay sample was investigated to synthesize the geopolymer. The analyses like X-ray fluorescence (XRF) spectroscopy for chemical composition, X-ray diffractometry (XRD) for mineral composition, and Fourier transform infrared (FT-IR) spectroscopy & scanning electron microscopy (SEM) for structural changes upon calcination at 500, 700 and, 900 °C were used to assess the suitability of selected lateritic clay sample for geopolymer. The drop in electrical conductivity and greater consumption of calcium hydroxide by CS-900 confirmed its potential reactivity than CS-700, CS-500, and CS-Control. The quality of geopolymer derived from un-calcined and calcined lateritic clay samples by alkali activation was evaluated by comparing results of compressive strength, water absorption test, and stability in the aggressive environment of chloride, FT-IR, XRD, and SEM analyses. The experimental results reveal that the quality of geopolymer enhances as the calcination temperature of the lateritic clay sample increases, However, calcination of the lateritic clay sample at 900 °C gives significant results and yield good quality geopolymer with 24.8 MPa of compressive strength, 7.07% of water absorption and 2.22% loss in mass in an aggressive environment.

Creep behavior and post-creep thermoelectric performance of the n-type Skutterudite alloy Yb0.3Co4Sb12

Upon uniaxial compressive loading at 500 °C (T/Tm = 0.67, where Tm is the absolute melting point), the n-type Skutterudite alloy Yb0.3Co4Sb12 deforms plastically by creep via a power-law, with a stress exponent ∼3 consistent with dislocation viscous glide. An activation energy of 171 kJ/mol is measured over the temperature range of 500–587 °C (T/Tm = 0.67–0.75) at a stress of 30 MPa. Yb0.3Co4Sb12 is ductile at 500 °C, exhibiting a compressive strain of 25% when subjected to stresses ranging from 22 to 90 MPa for up to 28 days. Among the thermoelectric materials tested so far for creep, Yb0.3Co4Sb12 exhibits a creep resistance intermediate between low-melting (Bi2Te3, TAGS-85) and high-melting thermoelectrics (Mg2Si and ZrNiSn). A relatively modest drop in the figure of merit zT, from 0.67 to 0.52, is displayed by Yb0.3Co4Sb12 after accumulating 3.7% compressive creep strain at 500 °C, mostly due to a drop in electrical conductivity.

Pozzolanic performance resemblance of milled sugarcane biomass ash using different pozzolanicity test methods

The improved pozzolanic efficiency of sugarcane biomass ash (SCBA) after selective milling is presented. The samples were prepared by milling the as-received SCBA in a vibrating cup mill for four different durations ranging between 30 s and 15 min. The SCBA was first analysed using physical (particle size distribution, specific gravity, bulk density, soundness, setting time and lime reactivity), chemical (X-ray fluorescence), mineralogical (X-ray diffraction) and morphological characterisation (scanning electron microscopy). In addition, the thermal stability of the as-received SCBA was checked to investigate its effect on the mineralogical phases. The samples were then tested for pozzolanicity using the strength activity index, drop in electrical conductivity, Chapelle activity and the amount of reactive silica. The relation between milling durations and the pozzolanicity was established using the analysis of variance technique. The linear model was found to be more significant and reliable as per the statistical regression analysis.

Design and investigation of sustainable pozzolanic material

Abstract The continuous growth of population and urbanization in India will guarantee a massive demand for cement in the near future. In view of sustainability, cement industry needs to develop the novel and effective pozzolans by proper recycling of alternative raw materials. The present study reports the suitability of boiler ash (BA) as a pozzolanic material. The preliminary characterization of BA is carried out by granulometric laser analysis, XRF, XRD, SEM, and TG analysis. To enhance the pozzolanicity of BA, it was processed mechanically and thermally which results in activation of silica. The pozzolanic characteristics of BA such as pozzolanic activity index (PAI), electrical conductivity drop (EC), Chapelle activity (CA), and the reactive silica (RS) were determined. The statistical regression model was also developed for the experimented pozzolanic properties. The linear regression models were best fitted with a coefficient of determination ranged between 0.84 and 0.98. The designed pozzolana is found as a sustainable and cost-effective solution to develop the cleaner environment for the cement production by minimizing the CO2 emissions.

Use of Processed Biomass Ash as a Sustainable Pozzolana

The industrial waste generated from sugar production, i.e. bagasse is further used as a biofuel. This generates a huge amount (44,000 tonnes/day) of waste in the form of sugarcane bagasse ash (SCBA). Asreceived boiler SCBA shows lower performance in terms of pozzolanic characteristics. In this study, the role of mechanical and thermal treatment in improving the pozzolanicity of SCBA has been examined. The preliminary characterization of SCBA was done using laser granulometry, SEM, XRF, XRD and TG analysis. The four methods were adopted to quantify the pozzolanic behaviour, viz. reactive silica determination, pozzolanic activity index, electrical conductivity drop and Chapelle activity. Further, the experimental data were analysed using ANOVA. The coefficient of regression (0.86–0.99) reflects effective and significant logarithmic models. The study concludes that the adopted processing of SCBA is highly effective in improving the pozzolanicity. Thus the processed SCBA is a sustainable solution to the cement industry.

Pressure-induced phase transitions for goethite investigated by Raman spectroscopy and electrical conductivity

ABSTRACTWe reported two pressure-induced phase transitions of goethite up to ∼35 GPa using a diamond anvil cell in conjunction with ac impendence spectroscopy, Raman spectra at room temperature. The first pressure-induced phase transition at ∼7.0 GPa is manifested in noticeable changes in six Raman-active modes, two obvious splitting phenomena for the modes and the variations in the slope of conductivity. The second phase transition at ∼20 GPa was characterized by an obviously drop in electrical conductivity and the noticeable changes in the Raman-active modes. The variations in activation energy with increasing pressure were also discussed to reveal the electrical properties of goethite at high pressure.

CASE STUDY ON NITRIFICATION RATES IN A NON-STIRRED MEMBRANE-AERATED BIOFILM REACTOR OPERATED UNDER LAMINAR REGIME

A lab-scale non-stirred membrane-aerated biofilm reactor with a volume of 14.2 L was operated under laminar flow regime with inorganic synthetic wastewater to assess tertiary nitrification rates. Nitrifying counter-diffusive biofilm grown over microporous polypropylene tubular membranes supplied with atmospheric air at low pressure (3.45 kPa). The reactor was operated at very low water-velocities (in cm/s): from 2.3×10-4 to 2.3 × 10-3. In all runs, the influent ammonium concentration was kept constant ( 26 mg-N/L). By changing the volumetric inflow, the membrane-aerated biofilm (MAB) was tested at seven different ammonium applied loads (range: 0.57 - 6.04 g-N/m2 d). The corresponding ammonium removal rates ranged 0.56 to 3.02 g-N/(m2 d). The percentage of biological ammonium removal presented a range from 50% to 98%. As expected, due to passive experimental dynamic conditions to achieve an ammonium removal percentage greater than 80% a hydraulic retention time of 19 h was required. Clean membrane oxygen transfer rate was evaluated. The nitrifying MAB was found to enhance the oxygen transfer across the membrane when the surface nitrification rates were high. A significant drop in electrical conductivity that is proportional to the ammonium removed was observed. Thus, conductivity measurement can be used as a simple control method of ammonium removal extent. Effluent suspended solids were not detected, therefore a sedimentation process was unnecessary.

CASE STUDY ON NITRIFICATION RATES IN A NON-STIRRED MEMBRANE-AERATED BIOFILM REACTOR OPERATED UNDER LAMINAR REGIME

A lab-scale non-stirred membrane-aerated biofilm reactor with a volume of 14.2 L was operated under laminar flow regime with inorganic synthetic wastewater to assess tertiary nitrification rates. Nitrifying counter-diffusive biofilm grown over microporous polypropylene tubular membranes supplied with atmospheric air at low pressure (3.45 kPa). The reactor was operated at very low water-velocities (in cm/s): from 2.3×10-4 to 2.3 × 10-3. In all runs, the influent ammonium concentration was kept constant ( 26 mg-N/L). By changing the volumetric inflow, the membrane-aerated biofilm (MAB) was tested at seven different ammonium applied loads (range: 0.57 - 6.04 g-N/m2 d). The corresponding ammonium removal rates ranged 0.56 to 3.02 g-N/(m2 d). The percentage of biological ammonium removal presented a range from 50% to 98%. As expected, due to passive experimental dynamic conditions to achieve an ammonium removal percentage greater than 80% a hydraulic retention time of 19 h was required. Clean membrane oxygen transfer rate was evaluated. The nitrifying MAB was found to enhance the oxygen transfer across the membrane when the surface nitrification rates were high. A significant drop in electrical conductivity that is proportional to the ammonium removed was observed. Thus, conductivity measurement can be used as a simple control method of ammonium removal extent. Effluent suspended solids were not detected, therefore a sedimentation process was unnecessary.

Effects of Lubricants and Nano-Inclusions on Copper Corrosion Behavior and Their Electrical Conductivity

In this work, the corrosion behavior of copper with inclusions in rolling oil is investigated via potentiodynamic polarization, electrochemical impedance spectroscopy and weight loss experiments. The relationships among surface morphologies of the corroded copper, their microstructure characteristics and electrical conductivity are discussed. The results show that the inclusions in copper were mainly copper oxides with grain size of about 40 nm. Etch pitting corrosion of copper was initiated by nano-inclusions assembled along grain and sub-grain boundaries. Dislocations and other crystallographic defects were found to accelerate corrosion reactions of copper. Compared with the relatively light corrosion, the worst corrosion electrical conductivity drop was about 35%. The worst corrosion induced the largest electrical conductivity drop to 51% after 21 h when specimens were immersed in rolling base oil with phosphate agent.

Processing and Characterization of Carbon Fiber Reinforced Aluminium7075

Materials required for Space applications need to have exceptional physical properties like low density coupled with high strength and stiffness. Carbon fiber (Cf) reinforced aluminium matrix composites are used as advanced materials in such applications. In order to study the effect of Pitch based carbon fiber on mechanical and electrical properties of aluminium (AA7075) matrix composite, the composite was manufactured by vacuum hot pressing. Various volume contents of carbon fibers were used to find out optimum fiber content which would give all-round mechanical and electrical properties. Effect of carbon fiber content on properties like hardness, strength and electrical conductivity was studied. The composite produced was rolled to find out its formability. The quality of composite manufactured was subsequently investigated by Optical microscopy, Scanning electron microscopy (SEM) and X-Ray Diffraction (XRD). The results indicate that the composite produced has uniform distribution of carbon fibers. Carbon fibers show good bonding with the matrix. Hardness and strength show drop as amount of carbon fiber increases. Drop in electrical conductivity is also observed with increase in fiber content, the same trend has been observed after T7 heat treatment. Although the trend is decreasing but increase in electrical conductivity is observed after the T7 treatment.