Increase In Resistivity Research Articles

Practical approach for sand-shale mixtures classification based on rocks multi-physical properties

Sandstones are the most common reservoir rocks, providing reservoirs for oil and gas and serving as reservoirs for groundwater. The Gulf of Mexico is known for its sand-shale mixtures and potential for its oil and hydrate gas resources in sandstone units. Understanding these variations is essential for assessing hydrocarbon potential and unconventional prospectivity. In this study, we utilized the Elastic, Electrical, and Radioactive (EER) properties of rocks for lithological categorization of well logging data, leading to the development of a novel rock physics template. The electrical and radioactive properties of the rocks facilitated a broad lithological classification, while their elastic characteristics helped distinguish between porous and low-porosity zones. Electrical and radioactive properties are utilized for well data classification because in sandstone formations, there is a decrease in log gamma and an increase in log resistivity. As a result, these opposing shifts in the two geophysical logs enhance the spread of data points on the lithological resistivity-gamma ray scatter plot, thereby simplifying the process of lithological categorization. Ultimately, the well logging data was sorted into three distinct categories: low shale sands (shale volume < 30 %), sand-shale mixtures (shale volume = 30 to 80 %), and shale-dominated areas. Subsequently, the Thomas Stieber model was employed to identify the types of clay minerals present in both sandstones and sand-shale mixtures. The model's findings revealed that dispersed type clay minerals are predominantly found in sandstones, with laminar and structured types being relatively rare. However, in sand-shale mixtures, both dispersed and laminar clays observed.

Epitaxial (AlxGa1−x−yIny)2O3 alloys lattice matched to monoclinic Ga2O3 substrates

We have epitaxially stabilized a series of monoclinic (AlxGa1−x−yIny)2O3 alloys by careful choice of molecular beam epitaxy growth conditions, which balance alloy growth with suboxide desorption. The films are pseudomorphic to (010) β-Ga2O3 substrates at thicknesses up to 150 nm with compositions ranging from (Al0.01Ga0.83In0.16)2O3 to (Al0.24Ga0.75In0.03)2O3. The absorption edge shifts from approximately 4.62–5.14 eV with coincidently increasing Al and decreasing In mole fractions. J–V measurements reveal an increase in resistivity over four orders of magnitude with a maximum value of 4.2 × 105 Ω-cm for (Al0.17Ga0.76In0.07)2O3, which has nearly identical lattice parameters (both in-plane and out-of-plane) to the underlying β-Ga2O3. Scanning transmission electron microscopy of this sample reveals a mostly uniform and single crystalline film, though we identify areas of non-uniform In incorporation and some γ-phase inclusions. This work demonstrates the feasibility of thick layers lattice-matched to β-Ga2O3 with increased bandgap compared to phase-separation limited (Al,Ga)2O3. These alloys can enable higher bandgap epitaxial dielectrics and high sheet charge density transistors by increasing the conduction band offset with respect to β-Ga2O3.

Micro–Macro-Analysis and Model Derivation of Electrical Resistivity of Ningxia Cement–Loess

In recent years, highway infrastructure in the Ningxia region of China has rapidly advanced. Cement–loess is extensively utilized in the roadbed and foundation reinforcement. It is necessary to conduct micro–macro-analysis and model derivation of the electrical resistivity on Ningxia cement–loess, which are beneficial for both the practical application of electrical resistivity and the evaluation of the geotechnical properties of cement–loess. Therefore, a series of electrical resistivity measurements, microstructural observations (scanning electron microscopy), mineral analyses (thermogravimetric analysis), and theoretical analyses were adopted on the cement–loess. The following conclusions can be drawn: The electrical resistivity is negatively related to dry density and water content, while it is positively related to cement dosage and curing age. A cement dosage of 6% exhibits a lower hydration reaction potential compared to 12%, causing a slower increase in electrical resistivity. The formation of calcium silicate gel around particles results in particle clustering and pore filling, reducing the pore area and increasing electrical resistivity. Increased hydration also decreases microscopic orientation, contributing to a higher electrical resistivity of cement–loess. Finally, a new three-dimensional electrical resistivity model was created, finding that the electrical resistivity of Ningxia cement–loess was determined by the dry density, water content (ρd·w), cement dosage, and curing age (aw·T) in an exponential function form. The new three-dimensional electrical resistivity model could be used in the high-efficiency evaluation of the cement–loess geotechnical parameter, offering valuable insights for the monitoring and maintenance of road infrastructure.

Characterization of the Anisotropic Electrical Properties of Additively Manufactured Structures Made from Electrically Conductive Composites by Material Extrusion.

Additive manufacturing (AM) of components using material extrusion (MEX) offers the potential for the integration of functions through the use of multi-material design, such as sensors, actuators, energy storage, and electrical connections. However, there is a significant gap in the availability of electrical composite properties, which is essential for informed design of electrical functional structures in the product development process. This study addresses this gap by systematically evaluating the resistivity (DC, direct current) of 14 commercially available filaments as unprocessed filament feedstock, extruded fibers, and fabricated MEX-structures. The analysis of the MEX-structures considers the influence of anisotropic electrical properties induced by the selective material deposition inherent to MEX. The results demonstrate that composites containing fillers with a high aspect ratio, such as carbon nanotubes (CNT) and graphene, significantly enhance conductivity and improve the reproducibility of MEX structures. Notably, the extrusion of filaments into MEX structures generally leads to an increase in resistivity; however, composites with CNT or graphene exhibit less reduction in conductivity and lower variability compared to those containing only carbon black (CB) or graphite. These findings underscore the importance of filler selection and composition in optimizing the electrical performance of MEX structures.

Effect of graphene on the key electrical, optical, and magnetic properties of polymethylmethacrylate: a study based on molecular modeling.

In this work, a new polymeric structure was designed consisting of a nanometric sheet of graphene (G) and a polymethylmethacrylate (PMMA) repeat unit, which was designated as PMMA-G. Three degrees of polymerization of PMMA-G were considered: monomer (PMMA-G1), dimer (PMMA-G2), and trimer (PMMA-G3). The effect of incorporating a nanometric sheet of graphene into the molecular structure of PMMA on the modification of some of its main optical, magnetic, and electrical properties was investigated. Currently, the study presented here is of great relevance since various areas of technology require new materials with specific properties for the development of new devices. The results of our study reveal that the dielectric constant of PMMA is reduced when graphene is incorporated. However, a percentage increase of 14.48% in the refractive index of PMMA when graphene is inserted to form the nanocomposite is observed. It is found that the absolute value of molar magnetic susceptibility of PMMA increases considerably when reinforced with graphene. Finally, when reinforcing PMMA with graphene to obtain the PMMA-G nanocomposite, the electrical resistivity increases by almost an order of magnitude. We used computational tools under Materials Studio (MS) software. We built a PMMA molecule with three degrees of polymerization, graphene sheet, and polymethylmethacrylate-graphene composite (PMMA-G) was built also with three degrees of polymerization using a concentration of 50% graphene over the PMMA polymer. For each structure, we used computational code DMol3 of MS, which is based on the Density Functional Theory, and the geometry optimization process was carried out to obtain the most stable structures. Finally, using the connectivity indices method together with topological properties of the molecular structures, implemented in Synthia computational code of MS software, we calculated the dielectric constant, magnetic susceptibility, refractive index, and electrical resistivity, for pure PMMA and PMMA-G structures for their three degrees of polymerization. The results were analyzed, and the changes in these properties were discussed in terms of the effect of an electric and magnetic field on the molecular structures of PMMA-G with respect to PMMA.

Influence of NH3 flow rate on the photoelectric properties of high Al content p-AlGaN.

High Al content (60%) p-AlGaN with different NH3 flow rates was grown using metal-organic chemical vapor deposition (MOCVD), and changes in its photoelectric properties were studied using the Hall effect tester (Hall) and cathodoluminescence (CL) spectrometer. The results show that the film resistivity increases from 3.8 Ω·cm to 46.5 Ω·cm with increasing NH3 flow rate. The impurity peak intensity of p-AlGaN grown under high NH3 flow conditions is particularly high, indicating numerous point defects. The results of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) show a large number of Ga interstitial atoms (Gai) at the interface. As Gai acts as a donor, this may be the main reason for the increase in resistivity. And under high NH3 flow conditions, a lattice distortion and a high density of dislocation occur between p-AlGaN and p-GaN, which can lead to enhanced carrier scattering and decreased mobility. Additional validation via LED growth experiments indicates that the luminescence intensity of samples with low ammonia concentration increased by more than 13000 times.

Effect of quenching and solubilization temperature on thermal, electrical, mechanical, and magnetic properties of a Heusler CuAlMnTiB alloy

We report a systematic investigation of the effect of quenching and solubilization temperature on the thermal, electrical, mechanical, and magnetic properties of the Heusler alloy CuAlMnTiB. The experimental procedure and the results obtained demonstrated that the tempering process can effectively adjust the physical properties of the CuAlMnTiB alloy. This treatment led to an increase in electrical resistivity, which went from 2.34×10−7Ω∙m in the raw melt sample (TBF) to 4.49×10−7Ω∙m in the sample quenching at 850 ºC (T850), in addition to an increase in the Curie temperature, from 297.5 ºC (TBF) to 305.85 ºC (T850). A decrease in remanent magnetization from 2.74 emu/g (TBF) to 0.31 emu/g (T850) and in the coercive field, which reduced from 54.15 Oe in the TBF to 4.55 Oe in the T850, was also observed. This makes tempering a viable alternative to adapt these properties to various technological applications, without requiring changes in the alloy composition. Here we were able to reach structural and magnetic properties compatible with those reported in the literature for CuMnAl alloys of different compositions.

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.

Effect of Proton Irradiation on Thin-Film YBa2Cu3O7-δ Superconductor.

We investigated the effect of 0.6 MeV proton irradiation on the superconducting and normal-state properties of thin-film YBa2Cu3O7-δ superconductors. A thin-film YBCO superconductor (≈567 nm thick) was subject to a series of proton irradiations with a total fluence of 7.6×1016 p/cm2. Upon irradiation, Tc was drastically decreased from 89.3 K towards zero with a corresponding increase in the normal-state resistivity above Tc. This increase in resistivity, which indicates an increase in defects inside the thin-film sample, can be converted to the dimensionless scattering rate. We found that the relation between Tc and the dimensionless scattering rate obtained during proton irradiation approximates the generalized d-wave Abrikosov-Gor'kov theory better than the previous results obtained from electron irradiations. This is an unexpected result, since the electron irradiation is known to be most effective to suppress superconductivity over other heavier ion irradiations such as proton irradiation. In comparison with the previous irradiation studies, we found that the result can be explained by two facts. First, the dominant defects created by 0.6 MeV protons can be point-like when the implantation depth is much longer than the sample thickness. Second, the presence of defects on all element sites is important to effectively suppress Tc.

DFT study of the brownmillerite-type strontium-based oxygen-deficient perovskites SrTMO2.5 (TM = Mn, Fe, Co and Cu)

DFT studies are performed to investigate the crystal structure and geometry, electronic and magnetic properties of brownmillerite-type strontium-based oxygen-deficient perovskites [Formula: see text] (TM = Mn, Fe, Co and Cu) in orthorhombic phase. The comparison of the calculated lattice parameters shows consistency with the experiments, and all these perovskites are thermodynamically stable as revealed by cohesive energy. The spin-dependent calculations of the electronic band profiles demonstrate the metallic behavior of all these deficient perovskites. The increase in electrical resistivity and electronic thermal conductivities with temperature also confirms the metallic behavior of these compounds. The optimized ground state energies in different magnetic phases and post-DFT treatment confirm that [Formula: see text] and [Formula: see text] are stable in C-type AFM, [Formula: see text] is in G-type AFM and [Formula: see text] in A-type AFM phase, respectively. The high specific heat of these deficient perovskites makes them good candidates for high-temperature technology. Based on the above physical properties, it is expected that these deficient perovskites are potential candidates for spintronics and magnetic storage devices.

Influence of the toxic vapors on the gas sensitivity and structure of poly(o-toluidine)

In the present work, we investigated the influence of the toxic vapors (ammonia, chloroform, tetrahydrofuran, dimethylformamide, nitrobenzene, toluene) on the specific resistance, optical absorption, and structure of conducting polymer poly-o-toluidine (PoT) obtained by oxidative polymerization of o-toluidine in toluene sulfonic acid (TSA) solution. This polymer has a high level of crystallinity and is thermal stable to 473 K (200 0C). The action of organic solvent vapors causes an increase in PoT-TSA resistance by 1.3-1.4 times, while after the action of ammonia, the resistivity increases almost 500 times. The activation energy of charge transfer Ea also increases from 0.21 to 0.71 eV under the action of ammonia due to the deprotonation of the polymer and its transformation to the resistive base form. When the organic solvents are used, the observed phenomena have a different direction (resistance increase or decrease) due to the peculiarities of polymer-solvent molecular interaction. This phenomenon may be used for selective detection of solvents.

What do we learn from impurities and disorder in high-Tc cuprates?

A series of experimental studies established that the differing morphologies of the phase diagrams versus hole doping nh of the various cuprate families are mostly controlled by defects and disorder. In the minimally disordered cuprate Yttrium Baryum Copper Oxide (YBCO) we introduced controlled detfects that allowed us to probe the metallic and superconducting states. We demonstrate that the extent of the spin glass phase and the superconducting dome can be controlled by the concentration of spinless (Zn, Li) impurities substituted on the planar Cu sites. NMR frequency shift measurements establish that these defects induce, in their vicinity, a cloud with a Kondo-like paramagnetic behavior. Its “Kondo” temperature and spatial extent differ markedly between the pseudogap and strange metal regimes. We have performed transport measurements on single crystals with a controlled content of in-plane vacancies introduced by electron irradiation. At high T, the inelastic scattering of the carriers has been found independent of disorder and completely governed by the excitations of the correlated electronic state. The low T upturns in the resistivity associated with single-site Kondo-like scattering are qualitatively in agreement with local magnetism induced by spinless impurities. The apparent metal insulator crossover is only detected for a very large defect content, and part of the large resistivity upturn remains connected with Kondo-like paramagnetism. In the superconducting state, the defect-induced reduction of Tc scales linearly with the increase in residual resistivity induced by disorder. High-field magnetoresistance experiments permit us to determine the paraconductivity due to superconducting fluctuations. The latter vanishes beyond a temperature T’c and a field H’c that both decrease with increasing in-plane defect content. In the pseudogap regime, the weaker decrease of T’c with respect to that of Tc reveals a large loss of superconducting phase coherence in the presence of disorder. In light of our experimental results, we initiate a discussion of its interplay with pair breaking. Our data also permit us to confirm that the differing phase diagrams are due to competing orders or disorders that are family-specific. In the ideal phase diagram of a disorder-free cuprate, 2D superconductivity should persist at low doping. This ensemble of experimental results provides serious challenges for the theoretical understanding of superconductivity in these correlated electron systems.

Additive effect of silicone resin on direct current arc quenching performance of a model electric fuse: electrical resistivity and thermal diffusivity of high-temperature Cu/SiO2 vapor mixed with C2H6SiO vapor decomposition

Concerning DC fuses equipped with silica sand (SiO2) as an arc quenching material, the authors have proposed an additive installation of silicone resin (C2H6SiO) on a fuse-element surface to improve the limitation and interruption ability of high DC. This paper describes the additive effect of the silicone resin on the transient resistance of the arc that has formed during the DC interrupting process in a model fuse, based on the measurement result that the arc resistance markedly rises with the silicone mass coated on the fuse element. This phenomenon is subsequently explained as resulting from a thermal diffusivity of high-temperature C2H6SiO/SiO2/Cu vapor. In other words, the mixing of C2H6SiO decomposition vapor into the arc can promote vapor temperature decay through the higher thermal diffusivity, resulting in a rapid increase in the electrical resistivity of the vapor during the DC interrupting process.

Large Rashba spin–orbit coupling in metallic SrTaO3 thin films

We fabricated conductive SrTaO3 epitaxial films on insulator substrates and measured the Rashba parameter using weak anti-localization analysis. The Rashba parameter, reaching up to 9.9 × 10−13 eVm, is the highest among metallic oxides and is comparable to the LaAlO3/SrTiO3 interface, which is widely used in Rashba effect studies. This indicates the potential for oxide-based spintronic devices. To use them as devices, it is important to investigate how film thickness affects the resistivity. Films ranging from 8.6 to 25 nm exhibited metallic conduction, but those thicker than 25 nm showed an unexpected increase in resistivity, suggesting instability of the meta-stable Ta4+ state.

Optimized TCR and MR properties of La0.7-xSmxCa0.3MnO3 ceramics by Sm3+ doping

La0.7Ca0.3MnO3 (LCMO), with its high temperature coefficient of resistance (TCR) and large magnetoresistance (MR) effect, has emerged as a leading material in the field of new multi-functional ceramics. Enhancing the magnetoresistive effect of LCMO in low magnetic field and expanding its application range is one of the main research goals of this kind of materials. In this work, La0.7-xSmxCa0.3MnO3 (LSCMO) (0≤x≤0.09) ceramic targets with different doping amounts were successfully prepared by sol-gel method, and the influence mechanism of Sm3+ doping on the magnetoresistive effect and electrical transport performance of LSCMO was systematically analyzed. X-ray diffraction (XRD) results showed that the lattice parameters (a,b,c,V) of LSCMO decreased slightly, indicating that the doping amount of Sm3+ at the A-site increased. Scanning electron microscopy (SEM) showed that the grains were closely connected without obvious pores, the grain size decreased slightly. The ρ-T curve shows an obvious metal-insulator (M-I) transition, with the increase of Sm3+, the increase of resistivity, metal-insulator transition temperature (TMI) and ferromagnetic-paramagnetic (FM-PM) transition temperature (TC) move towards low temperature. When x=0.015, the peak value of TCR reaches 41.94%·K-1, and when x= 0.06, the peak value of MR reaches 80.25%, both TCR and MR are improved. The results show that: Sm3+ doping can effectively enhance the electromagnetic transport performance of LSCMO. This material has a very wide application prospect in the fields of magnetic storage, and infrared detection.

Carbon fiber and PVA fiber reinforced concrete: Electrical resistivity and piezoresistive properties

This study examines the effects of carbon fiber (CF) and polyvinyl alcohol fiber (PVAF) on the mechanical and electrical properties of fiber-reinforced concrete by using four-electrode system and piezoresistive testing platforms. The optimal combination of 0.6 % CF and 0.6 % PVAF significantly improved piezoresistive properties, with a 45 % increase in relative resistivity. Additionally, 0.6 % CF with 0.9 % PVAF achieved a 13 % boost in compressive strength. SEM analysis revealed enhanced interfacial bonding between fibers, leading to improved mechanical and electrical performance. These findings highlight the composite’s potential for structural health monitoring, electromagnetic shielding, and winter snow removal applications

Synthesis of Samarium Nitride Thin Films on Magnesium Oxide (001) Substrates Using Molecular Beam Epitaxy

Rare-earth nitrides are an exciting family of materials with a wide variety of properties desirable for new physics and applications in spintronics and superconducting devices. Among them, samarium nitride is an interesting compound reported to have ferromagnetic behavior coupled with the potential existence of p-wave superconductivity. Synthesis of high-quality thin films is essential in order to manifest these behaviors and understand the impact that vacancies, structural distortions, and doping can have on these properties. In this study, we report the synthesis of samarium nitride monocrystalline thin films on magnesium oxide (001) substrates with a chromium nitride capping layer using molecular beam epitaxy (MBE). We observed a high-quality monocrystalline SmN film with matching orientation to the substrate, then optimized the growth temperature. Despite the initial 2 nm of growth showing formation of a potential samarium oxide layer, the subsequent layers showed high-quality SmN, with semiconducting behavior revealed by an increase in resistivity with decreasing temperature. These promising results highlight the importance of studying diverse heteroepitaxial schemes and open the door for integration of rare-earth nitrides and transition metal nitrides for future spintronic devices.

Near-bulk resistivity of sub-10nm Au films by breaking free from thickness downscaling effects

The miniaturization of electronic devices requires thin films with electrical conductivities that are comparable to those of bulk metals. However, ultrathin coinage metal films inevitably suffer from increased electrical resistivity compared with bulk metals, hindering their performance in miniaturized electronics. This study presents a novel approach to achieve near-bulk resistivity in sub-10-nm-thick Au films on heterogeneous oxide substrates. Our method utilizes O-incorporated epitaxial growth of Au films on α-Al2O3(0001) substrates followed by thermal treatment. This strategy promoted an exceptional film crystallinity, particularly favoring the Au(111) orientation, and significantly reduced the resistivity. Notably, the 8-nm-thick Au film exhibited a record-low resistivity of 3.7 μΩ⋅cm, approaching that of a significantly thicker (60-nm) Au film. This performance surpasses those of Cu and Ag film electrodes of similar thicknesses. Density functional theory calculations provided theoretical insights into the mechanism of O-induced epitaxial growth. Our findings demonstrate that improved crystallinity mitigates the strong dependence of resistivity on the thickness reduction. This study challenges the conventional view of resistivity increase in ultrathin metal films and offers a promising path toward high-performance miniaturized electronics with superior electrical properties.

Investigations on heat-generation stability and PTC effects of self-heating cement composites under diverse temperature conditions

In this study, the novel aspect lies in investigating heat-generation stability expressed as positive temperature coefficient (PTC) effects of self-heating cement under diverse temperature conditions. Self-heating cement composites were fabricated, and subjected to various types of heating tests including monotonic, cyclic, and long-term tests at three distinct temperatures: 25°C, 0°C, and −20°C. The results revealed a novel finding that the heat-generation performance decreased due to the increased electrical resistivity during the heating test, attributed to the PTC effect when high input voltage was applied. Conversely, the absence of PTC effect with low input voltage application resulted in a consistent temperature increase and negligible changes in electrical resistivity, particularly at low temperatures. These experimental findings provide valuable insights into the investigations on stability of heat-generation performance of self-heating cement composites, offering implications for their practical applications.

Fast fabrication of a hierarchical nanostructured multifunctional ferromagnet.

Materials with multifunctionality affect society enormously. However, the inability to surmount multiple functionality trade-offs limits the discovery of next-generation multifunctional materials. Departing from conventional alloying design philosophy, we present a hierarchical nanostructure (HNS) strategy to simultaneously break multiple performance trade-offs in a material. Using a praseodymium-cobalt (PrCo5) ferromagnet as a proof of concept, the resulting HNS outperforms contemporary high-temperature ferromagnets with a 50 to 138% increase in electrical resistivity while achieving their highest energy density. Our strategy also enables an exceptional thermal stability of coercivity (-0.148%/°C)-a key characteristic for device accuracy and reliability-surpassing that of existing commercial rare-earth magnets. The multifunctionality stems from the deliberately introduced nanohierarchical structure, which activates multiple micromechanisms to resist domain wall movement and electron transport, offering an advanced design concept for multifunctional materials.