Dc Resistivity Measurements Research Articles

2D nonlinear inversion of DC resistivity measurements, a case study; southeastern part of Ras El Dabaa, Northwestern coast, Egypt

The southern Mediterranean coast suffers from limited water resources as a result of exploitation of water supply, population growth, and climate change. Spatial lineaments and Seawater Intrusion (SWI) were detected at the southeast portion of Ras El Dabaa, on Egypt’s northwest coast, using the direct current resistivity (DCR) method. The Vertical Electrical Sounding (VES) data were acquired using Schlumberger array along four profiles and inverted both independently and jointly, aiming to obtain Two Dimensional (2D) geoelectrical images. The results of the one Dimensional (1D) inversion of VES data at each profile were stitched to form pseudo-2D sections on which the resistivity values and aquifer thickness in the southwest of the region appeared to be generally increasing, indicating a potential improvement in water quality.However, the results did not fully image the lateral variation but focused on the horizontal boundaries of the subsurface. On the contrary, the results of 2D inversion of the same data sets successfully managed to provide images that depicted resistivity distribution in both lateral and vertical directions. The detected sets of lineaments and fractured zones within the oolitic limestone and fossiliferous limestone units control the occurrence of groundwater in the region. The 2D inversion scheme revealed a low resistivity zone that indicated the presence of SWI and/or the dissolution of marine salts from the marine limestone bedrock of these aquifers in the northern portions of the studied area. Additionally, analysis of the 2D apparent porosity section shows how aquifers are connected by secondary porosity, which is defined by structures that resemble channels. The current approach offers valuable structural information for future planning and development of such complex geological coastal locations, taking into consideration the vulnerability of the groundwater system.

A new aspect of the effect of fluorine doping on structural and superconducting properties in the Bi2Sr1.6La0.4CuO5+δ(O1-xFx) ceramic system

In this study, ceramic samples with the nominal composition Bi2Sr1.6La0.4CuO5+δ(O1-xFx) (where x = 0, 0.2 and 0.4) were synthesized using the solid-state reaction method to investigate the effects of fluorine anionic doping on the Bi-2201 system's structural, microstructural, and superconducting properties. X-ray diffraction analysis (XRD) confirmed the Bi-2201 phase in all samples and total incorporation of fluorine. Doping with fluorine reduced orthorhombicity, leading to an orthorhombic-tetragonal transition. Scanning electron microscopy (EDS) revealed changes in grain shape and size, while energy dispersive x-ray analysis (EDAX) confirmed fluorine incorporation. DC-electrical resistivity measurements showed that fluorine doping decreased the critical transition temperature TC (Onset), with a greater decrease observed at higher fluorine concentrations. The resistivity increase in the normal state of the sample with x = 0.4 was also noted. The conduction mechanism above TC (Onset) = 26.10 K followed the Arrhenius law, indicating thermally activated behavior due to a band gap.

Enhancement of multiferrocity in CuCrO2 compounds through effective doping induced optimization of localized carrier holes and reduction in helical disorder

The bulk pristine CuCrO2, doped CuCr0.96M0.03V0.01O2 (M = Ti, Mn, Ga and Nb), CuCr0.96V0.04O2, CuCr0.97Mg0.03O2, CuCr0.97Ni0.03O2, and CuCr1-xFexO2 (x = 0.03, 0.06, and 0.09) compounds with single rhombohedral phase were investigated through low-temperature dc resistivity, field-dependent magnetization, and dielectric measurements. The room-temperature UV measurements were also carried out to determine possible changes in the optical bandgap due to the dopants mentioned above. The present work provides significant evidence of novel methodology for optimizing the number of localized carrier holes along with a reduction in helical disorder around MO6 octahedra, which leads to enhancement of the double exchange along the Cr-O-M-O linkages or superexchange between M3+/4+-Cr3+ mediated via oxygen. The nonmagnetic substitution in magnetic sublattice disrupts the spin spiral and a net weak component is realized in magnetization measurements.

Fluctuation induces conductivity and microstructural studies in Y-123: Effect of CaO inclusion

This study explored the impact of CaO as effective fine pinning centres on the interactions among thermodynamic fluctuations of superconducting parameters during the superconducting transitions in the Y-123 (YBa2Cu3O7-δ) matrix system. The investigation involved introducing varying concentrations (0.0100 wt% ≤ × ≤ 0.6000 wt%) of CaO into the Y-123 matrix through a green approach thermal treatment method annealed in an oxygen flow. TGA-DTA analysis revealed that the thermal stability of CaO exceeded that of the Y-123 matrix system. In XRD results, all specimens crystallized into orthorhombic Y-123 as the main phase, accompanied by non-superconducting phases such as Y-211 and BaCuO2, contributing to the enhancement of superconducting parameters. These inclusions of CaO induced distinct trends in grain degradation, spiral grain growth, and the appearance of homogeneous Y-123 nano-entities within the Y-123 matrix system. DC resistivity measurements investigating thermal fluctuation conductivity showed reductions in transition temperature widths (ΔTc and ΔTcMF1-offset) reaching an optimal concentration of CaO inclusion at 0.0375 wt%. Additionally, intra-granular current density at 0 K (Jc(0)) experienced significant improvements at lower concentrations, peaking at 0.0375 wt% at 11.0 ×106 A/m2. The incorporation of CaO at 0.0375 wt% proved optimal for achieving finely scaled lattice defects in intergranular and intragranular coupling, serving as effective pinning centres. This dominance in the 3D regime of thermal fluctuation reduced flux motion and improved Jc(0). The study concluded that the deficient inclusion of CaO led to the well-dispersed formation of nano-sized Y-123 particles, enhancing the superconducting parameters.

Phase transition and comparative study of CuxCd1–xS (x = 0.8, 0.6, 0.4, and 0.2) nanoparticle system

Microwave-assisted chemical precipitation was used to prepare CuxCd1–xS (x = 0.8, 0.6, 0.4, and 0.2) nanoparticles mixture. The crystal structure, size, and surface morphology of the as-synthesized nanoparticles were studied using X-ray diffraction and SEM. Presence of copper, cadmium, and sulphur in proper ratios in the samples was confirmed by energy-dispersed X-ray analysis. DC electrical resistance measurements of all the samples in the temperature range of 300…500 K showed phase transition above a certain temperature.

Correlation between structural, morphological, and electrical transport properties of nano-dimensional Tellurium thin film by low energy ion beam irradiation

Tellurium (Te), an emerging semiconductor material, exhibits intriguing physical properties in low-dimensional forms. This study investigates the structural, morphological, and transport properties of low-dimensional Te thin film deposited by physical vapor deposition after 400 keV Kr2+ ion irradiation with varying fluences of 1 × 1013, 5 × 1013, and1 × 1014 ions-cm−2. The X-ray diffraction (XRD) pattern reveals the hexagonal phase of pristine Te. As ion fluence increases, intensity of the XRD peaks decreases and the full-width half maxima (FWHM) increases, indicating a reduction in crystallinity. The intensity of the Raman peak decreases upon irradiation, resulting in a red shift in the spectra of the irradiated sample. The evolution of morphology at different fluences has been examined with atomic force microscopy (AFM) measurements. The results indicate the segregation of grains and an increase in root mean square (RMS) roughness from 2.59 pm to 5.11 pm with ion fluence up to 5 × 1013 ions-cm−2. At the highest fluence, i.e., 1 × 1014 ions-cm−2, there is an agglomeration of grains, and hence a decrease in RMS roughness to 3.92 pm is observed. The DC resistivity measurement indicates the semiconducting nature of all films. Additionally, this measurement signifies the rapid decrease in activation energy at both band-to-band conduction and nearest neighbour hopping (NNH) conduction. Following irradiation, Hall measurement demonstrates a decrease in the concentration of charge carriers and an increase in resistivity due to scattering originating from grain boundaries. However, when the fluence is increased to 1 × 1014 ions-cm−2, there is a reduction in resistivity and an increase in carrier concentration with enhanced Hall mobility in comparison to pristine Te. Therefore, this study showcases that low-energy ion irradiation has a significant impact on the modification of the structure, morphology, and electrical transport properties of semiconducting Te thin film.

Salinity distribution in agricultural land by geophysical, hydrochemical and geostatistical approaches: a pilot area located in Qelabshowah–Belqas, East Nile Delta region, Egypt

The study area is situated in the Qelabshowah–Belqas region, known for its Quaternary deposits. This research aims to demonstrate the two-dimensional (2D) variation of subsurface layers and salinity distribution using geoelectrical data, hydrochemical analysis, and geostatistical analysis. DC resistivity measurements were taken at fifteen vertical electrical sounding (VES) survey points using a Schlumberger array (AB/2 = 100 m) along three profiles. In addition, an electrical resistivity tomography (ERT) survey was conducted with a dipole–dipole array across one profile. Seven surface water samples were collected in the area. From the 1D and 2D inversion of VES and ERT data sets, three-to-four geoelectric layers were identified, including unconsolidated surface deposits, saturated clayey sand, saturated sand, and a salt-rich layer. The 2D inversion of VES data revealed an ancient salt-rich layer deposited in swampy conditions over a conductive wet sand layer along profile one due to salt mineral infiltration and dissolution. The 2D inversion of ERT data showed accurate lateral geometric accuracy compared to the 2D inversion of VES data, highlighting geological features, such as caves in the second layer and a buried water canal on the ground surface. Surface water samples showed high salinity levels with sodium hazards, indicating an Na–Cl composition. Geoelectric and hydrochemical data sets were geostatistically analyzed using spherical variogram supported ordinary Kriging interpolation. The analysis indicated weak to moderate spatial dependency for true resistivity parameters, while sodium content (SC) and permeability index (PI) showed strong spatial correlation. The 2D spatial distribution resistivity maps based on the 1D inversion of VES data displayed a general decrease in resistivity with depth, likely due to clay minerals or moist soil in the second layer and saline irrigation water infiltration in the third layer. The 2D spatial distribution of SC and PI showed a high concentration zone, posing a potential risk to agricultural crops regardless of soil permeability. It is recommended to use these maps when cultivating plants that can tolerate high sodium levels during the reclamation process.

Design and Implementation of a Three-phase Asynchronous Motor Intelligent Test System

Background: The locomotive traction motor has gradually shifted from DC motors to AC motors in high-speed railways, and the traction motor needs to be regularly maintained and tested frequently. Objective: The aim of this study was to test the related motor performance by obtaining and analyzing motor data from the test according to the standard "Three-phase Asynchronous Motor Test Method (GB-T 1032-2012)". The performance of the tested motor has been evaluated to meet the relevant requirements of the application. Thus, reasonable and scientific references have been offered for the maintenance and repair of the motor. Methods: A three-phase AC asynchronous motor test system based on LabVIEW and an AC power dynamometer was constructed based on the needs of the factory and type test of a three-phase AC asynchronous motor. Ambient temperature measurement, insulation resistance measurement, DC resistance measurement, no-load characteristics test, overspeed test, blocking characteristics test, load test, and temperature rise test have been carried out. The data on voltage, current, speed, power, and so on, have been collected. A 125 kW three-phase asynchronous motor was tested with the designed system, and the parameters obtained from the system were compared with those from the motor labels. Results: The three-phase AC asynchronous motor test system was designed based on LabVIEW and AC dynamometer operating on an industrial computer with a precision measuring instrument. The most advanced virtual instrument technology was used to combine the powerful data computing and processing ability with the measurement and control ability of instrument hardware. The software proved to be able to acquire data display, control, storage, and analysis simultaneously. In addition, a high degree of intelligence, an automatic motor start and stop control, automatic synchronous acquisition of test data, automatic data processing and calculation, and automatic test report generation and printing function were covered in this system. The simulated results of the system agreed well with the actual performance of the three-phase asynchronous motor, and helped the motor to operate well. Conclusion: The designed testing system exhibited a high automation ability, reliability, and accuracy. It proved to be a time and manpower-saving technical method, improving the actual test efficiency, and helped to reduce labor intensity dramatically.

Structural investigation, magnetic and DC electrical resistivity properties of Co0.5-xNixZn0.5Fe2O4 nano ferrites

The Ni2+ substituted Cobalt-Zinc nano ferrites, designated as Co0.5-xNixZn0.5Fe2O4 with x values ranging from 0.0 to 0.5, were synthesized using the sol–gel auto-combustion method. Various characterization techniques, including x-ray diffraction (XRD), field-effect scanning electron microscopy (FESEM), Fourier Transform Infrared (FTIR) spectroscopy, vibrating sample magnetometer (VSM), and DC electrical resistivity measurements, were employed to analyze the prepared samples. XRD analysis revealed a cubic spinel structure with a lattice constant ranging from 8.384 to 8.412 Å. FESEM examination indicated non-uniform-shaped spherical grains in the nanometer range for the synthesized samples. The FTIR spectra of the spinel ferrites revealed two distinctive bands, ν2 (580–592 cm−1) and ν1 (390–412 cm−1), which are the characteristics of spinel-structured ferrite nanomaterials. With progressive substitution (x varying from 0.0 to 0.5), the saturation magnetization (Ms) values exhibited a gradual decrease, starting from Ms = 60.97 emu/g (at x = 0.0) and reaching Ms = 38.79 emu/g (at x = 0.5). A discernible pattern was observed in coercivity (Hc), which rose from Hc = 115 Oe (at x = 0.0) to Hc = 920 Oe (at x = 0.5), with peak values determined through VSM analysis. Similar to semiconductors, the electrical resistivity experienced a decline with increasing temperature, indicative of a negative temperature coefficient.

Tailoring the structural, optical, electrical and multiferroic properties of Sm1-xRxFeO3 (x = 0.0 and 0.5; R = Pr, Nd, and Gd) and their synergistic photocatalytic activity

In this work, nanocrystalline Sm1-xRxFeO3 (x = 0.0 and 0.5; RPr, Nd, and Gd) samples have been synthesized via auto-combustion method and characterized to understand their microstructural, optical, electrical and multiferroic properties. X-ray diffraction data in combination with the FTIR spectra revealed the monophase and distorted orthorhombic configuration of all the samples with Pbnm space group. Rietveld refinement displayed a reduction in the bond length as well as the bond angle in the Sm0.5Gd0.5FeO3 sample. Raman spectra exhibit compressive strain in Sm0.5Gd0.5FeO3 nanoparticles; this finding is further supported by the XRD analysis. UV–visible spectroscopy manifests a reduction in the optical energy bandgap on moving Gd to Pr in Sm0.5R0.5FeO3 system. Transmission electron microscopy (TEM) images in combination with energy dispersive x-ray (EDX) spectra reveal the non-uniform surface morphology with the agglomerated nature of nanoparticles and affirm the elemental compositions of all the samples. The room temperature P-E and M − H loops infer the multiferroic nature of all samples. Electron paramagnetic resonance (EPR) analysis divulges the weakening of the super-exchange interactions in Sm0.5R0.5FeO3 system. DC electrical resistivity measurements reflect semiconductor-like behaviour in all prepared samples. The dielectric behaviour of the samples is in accordance with the “universal dielectric response” model. The temperature-dependent dielectric measurements of all prepared samples have been performed at 1 kHz to determine the Néel temperature (TN). The photocatalytic investigation depicts the superior photocatalytic response of Sm0.5Pr0.5FeO3 nanoparticles under solar-light irradiation through the synergism of semiconductor-photocatalyzed oxidation and heterogeneous Fenton-like reaction.

DC Resistance Measurements in Multi‐Layer Additively Manufactured Yttrium Barium Copper Oxide Components

Additive manufacturing can offer new methods to shape materials that are difficult or too brittle in nature to process traditionally. In this work the optimization of a linseed oil and ICP solvent based solution with 90 wt% solid loading of the high temperature superconducting material yttrium barium copper oxide (YBCO) for additive manufacturing is demonstrated. The post sintered, printed components are analysed using a combination of X‐ray diffraction, scanning electron microscopy (SEM), magnetometry, and DC transport measurements. It is shown for the first time, for multilayer additively manufactured YBCO, direct DC transport measurements that indicate a current carrying percolative path with an upper transition temperature of 86.5 K.

Conduction mechanism of Gd2O3 induced by CO2 under in-field conditions

This work investigates the conduction mechanism of hydrothermally grown Gd2O3-sensitive material in order to explain its electrical resistance behaviour when exposed to increasing concentrations of CO2 under in-field conditions. To achieve this, the experimental investigation began with X-ray photoelectron spectroscopy of the Gd2O3 microstructure to verify the oxidation states of the surface. Subsequently, the impact of constant atmospheric factors such as oxygen and relative humidity on the electrical resistance of the Gd2O3 layer was examined. Finally, a progressive dosing of CO2 concentrations ranging from 400 to 3000 ppm was conducted. The DC electrical resistance measurements were performed using a computer-controlled Gas Mixing System operated under a dynamic gas flow regime. Experimental data was validated using the Boltzmann distribution statistics and the grain-to-grain Schottky barrier model. The results highlight the preservation of the n-type semiconductor behaviour of Gd2O3 irrespective of the background relative humidity and bring the oxidising character of CO2 to the fore.

Comparative investigation of low and high pelletize pressure for (Ag)x/CuTl-1223 nanoparticles-superconductor composites

This article experimentally investigates the impact of silver (Ag) nano-particles inclusion and high pelletized pressure on the structural, morphological, and electrical properties of Cu0.5Tl0.5Ba2Ca2Cu3O10−δ (noted CuTl-1223) bulk system. The nano-(Ag) x /CuTl-1223 composites were synthesized using a two-step solid-state reaction process with added amount of Ag nano-particles ranging from 0 to 2.0 wt% of the total mass. These nano-composites were produced at both low and high pelletize pressure of 0.202 GPa. All prepared samples were characterized using valuable techniques such as X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FTIR), and dc-resistivity measurement at low as well as high pelletized pressure, respectively. The structural investigation via the XRD technique indicated that Ag NPs did not affect the CuTl-1223 tetragonal structure, confirmed that Ag nano-particles were settled across the grain boundaries. SEM examination revealed a fine distribution of nano-sized silver (Ag) NPs among the CuTl-1223 grains, as well as improved weak-links and density of void/pores. The position of distinct vibrational oxygen modes in FTIR spectra showed no substantial alteration, indicating that the structural nature of the host CuTl-1223 phase was preserved. The electrical properties were studied using the four-point probe technique, and the activation energy were determined using Arrhenius law. The results of measurements showed that pelletization pressure of 0.202 GPa have an impact on the critical temperature of (Ag) x /CuTl-1223 composites. The superconducting critical temperature was enhanced from 99 K to 107 K at high-pressure of pelletization (0.202 GPa) as compared to low pressure, with = 0 ∼ 2.0 wt nano-particles addition to the host CuTl-1223 phase.

Enhanced DC electrical resistivity and magnetic properties of transition metal cobalt substituted spinel MgFe2O4 ferrite system

Cobalt-substituted magnesium ferrite materials, denoted as Mg1-xCoxFe2O4 (with × = 0.0, 0.25, 0.5, and 0.75), were synthesized using the solid-state reaction method at 1200 °C. This study aimed to investigate these ferrite systems' morphology, structure, DC electrical resistivity, and magnetic characteristics. Various analytical techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), Fourier-transform infrared (FT-IR) spectroscopy, DC electrical resistivity measurements, and vibrating sample magnetometer (VSM), were employed to assess the phase purity, microstructure, elemental composition, functional groups, resistivity, activation energy, and magnetic properties of the ferrite particles. The XRD patterns revealed a spinel cubic structure with the Fd3m space group. SEM images exhibited a few agglomerations and grains with spherical and polyhedral shapes, measuring 1.5 to 2 µm. The FTIR spectrum displayed two wavebands (ν1 and ν2) in the range of 400 cm−1 to 600 cm−1, corresponding to the lattice's tetrahedral and octahedral sites. Activation energies, which increased with higher cobalt concentrations, were calculated from DC electrical resistivity measurements. Furthermore, saturation magnetization and coercivity values gradually increased with rising cobalt concentrations.

Synthesis, structural, magnetic properties and DC electrical resistivity of Cr3+ substituted Mg-Ni ferrites

The solid-state reaction route synthesised Mg0.5Ni0.5Fe2-xCrxO4 (x = 0.0, 0.2, 0.4, and 0.6) ferrites. The XRD, SEM, FT-IR spectroscopy, VSM, and DC electrical resistivity measurements were used to measure the synthesized materials' crystal structure, microstructure, crystallite size and magnetic and resistivity properties, respectively. XRD analysis confirms the materials' efficient synthesis and improvement of crystallite sizes in a single-phase cubic spinel structure. The lattice constant in the ranges (8.423–8.362 Å) and crystallite size (45.02–26.51 nm) were measured and are shown to decrease when chromium ions increase. SEM analysis was done to understand the morphology and grain structure. Infrared (IR) spectroscopy was used to confirm the inherent vibrational absorption bands for the tetrahedral and octahedral sites of the spinel structure. With the addition of chromium ions, it has been observed that the saturation magnetization in the ranges of (34.58–62.15 emu/g), remanent magnetization (3.68–15.24 emu/g), and coercivity (145.21–155.13 Oe) were calculated with an increases pattern with the concentration level of the dopant. The M−H curves were drawn using VSM at room temperature for all compositions, and the hysteresis parameters were calculated. At a surface area of 15 KOe, hysteresis loops in prepared samples exhibit high saturation, and loops are highly symmetrical. The conventional semiconducting behavior of spinel ferrites is provided by the DC resistivity assessed using the two-probe technique, which shows a decrease in resistivity as temperature increases.

Development of modulation, pairing mechanism, and slip system with optimum vanadium substitution at Bi-sites in Bi-2212 ceramic structure

Present study focuses extensively on the change in electrical, superconducting and microhardness parameters with partial substitution of trivalent V+3 impurities replacing Bi+3 ions in Bi-2212 ceramic compound with the aid of dc electrical resistivity and microhardness test measurements. Experimental findings, calculation results, and phenomenological discussions provide that the optimum vanadium substitution level is found to be x = 0.01 in the Bi2.0-xVxSr2.0Ca1.1Cu2.0Oy (Bi-2212) ceramic system for the highest conductivity, crystallinity quality, superconducting, and mechanical performance features depending on the decreased microscopic structural problems. All the findings are wholly verified by scanning electron microscopy (SEM) and X-Ray diffraction (XRD) analyses. The dc electrical measurements indicate that the optimum vanadium ions support the pairing mechanism for the formation of new polaronic states in the clusters of microdomains, and hence expand superconducting energy gap due to the enhancement of amplitude part of pair wave function in the spin-density wave systems. The excess vanadium content degrades all the basic thermodynamics and quantum mechanical quantities mentioned due to the stress-induced phase transformation. Numerically, the Bi-2212 advanced ceramic matrix prepared by the optimum vanadium impurity is noticed to present the smallest residual resistivity value of 0.08 mΩ cm, room temperature resistivity value of 8.84 mΩ cm, and broadening degree of 0.36 K. Similarly, the ceramic material is found to possess the highest residual resistivity ratio of 3.05, carrier concentration number of 0.153041, critical transition offset and onset value of 84.66 K and 85.02 K, respectively. Besides, the microhardness findings reveal that the same compound with the least sensitivity to the applied test loads exhibits the largest Hv value of 4.799 GPa, Young's moduli of 393.303 GPa, yield strength of (0.969 GPa), and elastic stiffness coefficient of 15.5574 (GPa)7/4 under the applied test load of 0.245 N. The XRD investigations show that the presence of optimum vanadium impurity supports the formation of a high superconducting phase, c-axis length, and average crystallite size. All the findings are morphologically confirmed by the SEM images. It is found that the crystallographically best crystallinity quality and view of surface morphology is observed for the optimum vanadium substitution level. All in all, new higher properties for the conductivity, crystallinity quality, surface morphology, superconducting, and microhardness parameters based on the optimum vanadium replacement encourage the Bi-2212 crystal system to use in much more application places.

Simultaneously-doping of HfO2 thin films by Ni with sputtering technique and effect of post annealing on structural and electrical properties

This article reports a detailed structural and electrical characterization study of Ni:HfO2 dielectrics grown by rf and dc sputtering and variations in the rapid thermal annealing temperature. Annealing produced obvious changes in the morphological structure of films and XRD confirmed that the crystallite size increased from 1.3 nm to 14.4 nm with the annealing temperature. XPS showed that the amount of non-lattice oxygen decreased owing to the effects of annealing and resistivity. Dc resistivity measurements showed that the lowest sheet resistance of 1.182 × 106 Ω/□ was achieved by as-deposited films and increased to 70.960 Ω/□ with annealing. Structural differences in films due to the effect of annealing caused equivalent circuit models to vary and different resistance values in electrochemical impedance spectrometry. This study illustrates that HfO2 thin films, boosted by doping and rapid thermal annealing, provide a route toward advanced gate oxide stack structures in electronic devices beyond conventional high-dielectric-constant materials.

Metal-to-Insulating Transition in the Perovskite System YSr2Cu2FeO8-δ (0 < δ < 1) Modeled by DFT Methods.

Progress in the design of functional perovskite oxides relies on advances in density functional theory (DFT) methods to efficiently and effectively model complex systems composed of several transition-metal ions. This work reports the application of DFT methods to investigate the electronic structure of the YSr2Cu2FeO8-δ (0 < δ < 1) family in which the insulating, metal, or superconducting behaviors and even anion conductivity can be tuned by modifying the oxygen content. In particular, we assess the performance of the generalized gradient approximation (GGA), its Hubbard-U correction (GGA + U), and the strongly constrained and appropriately normed (SCAN) to model the metallic (idealized YSr2Cu2FeO8) and insulating (idealized YSr2Cu2FeO7) phases of the system. The analysis of the DFT results is supported by DC resistivity measurements that denote the metal character of the synthesized YSr2Cu2FeO7.86 and the semiconducting character of YSr2Cu2FeO7.08 prepared under reducing conditions. In addition, the band gap of YSr2Cu2FeO7.08, in the range of 0.73-1.2 eV, has been extracted from diffuse reflectance spectroscopy (DRS). While the three methodologies (GGA, GGA + U, SCAN) permit the reproduction of the crystal structures of the synthetized oxides (determined here in the case of YSr2Cu2FeO7.08 by neutron powder diffraction (NPD)), the SCAN emerges as the only one capable to predict the basic electronic and magnetic properties across the YSr2Cu2FeO8-δ (0 < δ < 1) series. The picture that emerges for the metal (δ = 0) to insulating (δ = 1) transition is the one in which oxygen vacancies contribute electrons to the filling of the Cu/Fe-3dx2-y2 states of the conduction band. These results validate the SCAN functional for future DFT investigations of complex functional oxides that combine several transition metals.

Study of the Structural and Electrical Properties of Bi2-xAgxBa2-ySryCa2Cu3O10+δ System

This study included preparing samples of the compound (Bi2Ba2Ca2Cu3O10+δ) by the solid state reaction method under a hydrostatic pressure 8 ton/cm2 and annealing temperature 840oC. X-ray diffraction (XRD), scanning electron microscopy (SEM), dc electrical resistivity measurements by four point probe method were used to investigate the microstructural and superconducting properties of Bi¬2223 samples. The X-rays diffraction study for the compound (Bi2Ba2Ca2Cu3O10+δ ) showed that it has Tetragonal type of crystal structure. The partial replacement of the component Ag in Bi, and Sr component in Ba simultaneously, the compound becomes (Bi2-xAgxBa2-ySryCa2Cu3O10+δ) with (x ,y) values equal to (x= 0.2, y= 0.1, 0.2, 0.3,0.4). The study of the crystal structure test showed that the structure retains on the tetragonal type with a high Tc phases (2223), low Tc phase(2212) and impurity phases, and the critical temperature Tc steps-up from (125K) to (137K) at substitution rate (x= 0.2, y= 0.1). But at increasing the substitution rate for (y) and the stability of (x) rate more than (x= 0.2, y= 0.1), the temperature declines to (108 K). Finally, the microstructural of the samples has been studies and tested by Scanning Electron Microscope for knowing the components' rates in the compound; how the compound partial substitution affect in the components; and specifying the quantitative and qualitative rates of the components in the compound.

Optics-Free, In Situ Swelling Monitoring of Articular Cartilage with Graphene Strain Sensors.

Articular cartilage derives its load-bearing strength from the mechanical and physiochemical coupling between the collagen network and negatively charged proteoglycans, respectively. Current disease modeling approaches and treatment strategies primarily focus on cartilage stiffness, partly because indentation tests are readily accessible. However, stiffness measurements via indentation alone cannot discriminate between proteoglycan degradation versus collagen degradation, and there is a lack of methods to monitor physiochemical contributors in full-stack tissue. To decouple these contributions, here, we developed a platform that measures tissue swelling in full-depth equine cartilage explants using piezoresistive graphene strain sensors. These piezoresistive strain sensors are embedded within an elastomer bulk and have sufficient sensitivity to resolve minute, real-time changes in swelling. By relying on simple DC resistance measurements over optical techniques, our platform can analyze multiple samples in parallel. Using these devices, we found that cartilage explants under enzymatic digestion showed distinctive swelling responses to a hypotonic challenge and established average equilibrium swelling strains in healthy cartilage (4.6%), cartilage with proteoglycan loss (0.5%), and in cartilage with both collagen and proteoglycan loss (-2.6%). Combined with histology, we decoupled the pathologic swelling responses as originating either from reduced fixed charge density or from loss of intrinsic stiffness of the collagen matrix in the superficial zone. By providing scalable and in situ monitoring of cartilage swelling, our platform could facilitate regenerative medicine approaches aimed at restoring osmotic function in osteoarthritic cartilage or could be used to validate physiologically relevant swelling behavior in synthetic hydrogels.