Normal Resistivity Research Articles

Hydrostatic pressure effect on the transport properties in TiO superconducting thin films

The superconducting properties of the TiO epitaxial thin films were systematically investigated under hydrostatic pressures $(P)$ up to 2.13 GPa. At ambient pressure, the normal state resistivity increases with decreasing temperature, and steeply increases below ${T}_{\mathrm{kink}}\ensuremath{\sim}115\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. With further reducing temperature to ${T}_{c}\ensuremath{\sim}5.99\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, the thin film enters into a superconducting state. Interestingly, the superconducting temperature ${T}_{c}$ gradually decreases upon increasing $P$, and the decreasing rate of ${T}_{c}$ with $P$ is much larger than the McMillan theoretical expectation. In contrast, ${T}_{\mathrm{kink}}$ increases with $P$ and a remarkable resistivity enhancement was observed in the temperature range between ${T}_{\mathrm{kink}}$ and ${T}_{c}$. The variations of ${T}_{c},{T}_{\mathrm{kink}}$, and normal state resistivity under high pressure may be induced by the charge localization related to the atomic vacancies rearrangement in TiO thin film. Furthermore, the temperature dependencies of the upper critical field ${H}_{c2}(T)$ indicate that both the orbital and Pauli-paramagnetic pair-breaking effects should be taken into account. Finally, the thermally activated flux flow investigations under different pressures suggest that the pressure will suppress the thermal activate energy.

Infield superconducting properties of nano-sized Ag added Cu0.5Tl0.5Ba2Ca2Cu3O10−δ

Infield superconducting properties of {(Ag)x/CuTl-1223}; (x = 0, 0.5, 1.0, 2.0 and 4.0wt %) nanoparticles-superconductor composites were investigated under different applied magnetic field up to H = 8T. The increase in critical temperature {Tc(0)} and decrease in normal state resistivity (ρo) were observed with increasing contents of Ag nanoparticles in CuTl-1223 superconducting matrix. The value of Tc°nset (K) remained almost unaffected by applying external magnetic field, but a decreasing trend in Tc (0) was observed by increasing the value of external applied magnetic field. The transition region below Tc°nset (K) showed Arrhenius behavior due to thermally activated flow of magnetic vortices. Enhancement in flux flow activation energy (Uo) and suppression in transition width (ΔT) of CuTl-1223 phase with addition of Ag nanoparticles showed the improvement in flux pinning strength of superconductor.

The effect of growth temperature on the irreversibility line of MPMG YBCO bulk with Y2O3 layer

In this study, three kinds of YBCO samples which are named Y1040, Y1050 and Y1060 were fabricated by Melt–Powder–Melt–Growth (MPMG) method without a seed crystal. Samples seem to be single crystal. The compacted powders were located on a crucible with a buffer layer of Y2O3 to avoid liquid to spread on the furnace plate and also to support crystal growth. YBCO samples were investigated by magnetoresistivity (ρ–T) and magnetization (M–T) measurements in dc magnetic fields (parallel to c–axis) up to 5T. Irreversibility fields (Hirr) and upper critical fields (Hc2) were obtained using 10% and 90% criteria of the normal state resistivity value from ρ–T curves. M–T measurements were carried out using the zero field cooling (ZFC) and field cooling (FC) processes to get irreversible temperature (Tirr). Fitting of the irreversibility line results to giant flux creep and vortex glass models were discussed. The results were found to be consistent with the results of the samples fabricated using a seed crystal. At the fabrication of MPMG YBCO, optimized temperature for crystal growth was determined to be around 1050–1060°C.

The bipolaron model in transport properties of YBa2Cu3Oy superconductor prepared by adding Pr2Co7 magnetic nanoparticles

Samples with the addition of ferromagnetic nanoparticles of Pr 2 Co 7 on YBa 2 Cu 3 O y (YBCO) polycrystalline superconductor were prepared by the standard solid state reaction method. The analysis of x-ray diffraction patterns by Rietveld refinement indicates orthorhombique to tetragonal phase transformation and oxygen rate reduction from x=0.3% of Pr 2 Co 7 content. Resistivity at room temperature increases as Pr 2 Co 7 content increases. The normal state resistivity versus temperature was analyzed properly by the bipolaron model. It suggested the increase of mobile charge localization with Pr 2 Co 7 content. Keywords: Pr 2 Co 7 ferromagnetic nanoparticles, high temperature superconductor, bipolaron model, localization of mobile charge

Preferred Orientation Contribution to the Anisotropic Normal State Resistivity in Superconducting Melt-Cast Processed Bi₂Sr₂CaCu₂O8+δ.

We describe how the contribution of crystallographic texture to the anisotropy of the resistivity of polycrystalline samples can be estimated by averaging over crystallographic orientations through a geometric mean approach. The calculation takes into account the orientation distribution refined from neutron diffraction data and literature values for the single crystal resistivity tensor. The example discussed here is a melt-cast processed Bi2Sr2CaCu2O8+δ (Bi-2212) polycrystalline tube in which the main texture component is a <010> fiber texture with relatively low texture strength. Experimentally-measured resistivities along the longitudinal, radial, and tangential directions of the Bi-2212 tube were compared to calculated values and found to be of the same order of magnitude. Calculations for this example and additional simulations for various texture strengths and single crystal resistivity anisotropies confirm that in the case of highly anisotropic phases such as Bi-2212, even low texture strengths have a significant effect on the anisotropy of the resistivity in polycrystalline samples.

Marine‐controlled source electromagnetic study of methane seeps and gas hydrates at Opouawe Bank, Hikurangi Margin, New Zealand

AbstractMarine controlled source electromagnetic (CSEM) data have been collected to investigate methane seep sites and associated gas hydrate deposits at Opouawe Bank on the southern tip of the Hikurangi Margin, New Zealand. The bank is located in about 1000 m water depth within the gas hydrate stability field. The seep sites are characterized by active venting and typical methane seep fauna accompanied with patchy carbonate outcrops at the seafloor. Below the seeps, gas migration pathways reach from below the bottom‐simulating reflector (at around 380 m sediment depth) toward the seafloor, indicating free gas transport into the shallow hydrate stability field. The CSEM data have been acquired with a seafloor‐towed, electric multi‐dipole system measuring the inline component of the electric field. CSEM data from three profiles have been analyzed by using 1‐D and 2‐D inversion techniques. High‐resolution 2‐D and 3‐D multichannel seismic data have been collected in the same area. The electrical resistivity models show several zones of highly anomalous resistivities (&gt;50 Ωm) which correlate with high amplitude reflections located on top of narrow vertical gas conduits, indicating the coexistence of free gas and gas hydrates within the hydrate stability zone. Away from the seeps the CSEM models show normal background resistivities between ~1 and 2 Ωm. Archie's law has been applied to estimate gas/gas hydrate saturations below the seeps. At intermediate depths between 50 and 200 m below seafloor, saturations are between 40 and 80% and gas hydrate may be the dominating pore filling constituent. At shallow depths from 10 m to the seafloor, free gas dominates as seismic data and gas plumes suggest.

Pressure induced change in the electronic state of Ta4Pd3Te16

We present measurements of superconducting transition temperature, resistivity, magnetoresistivity and temperature dependence of the upper critical field of Ta$_4$Pd$_3$Te$_{16}$ under pressures up to 16.4 kbar. All measured properties have an anomaly at $\sim 2 - 4$ kbar pressure range, in particular there is a maximum in $T_c$ and upper critical field, $H_{c2}(0)$, and minimum in low temperature, normal state resistivity. Qualitatively, the data can be explained considering the density of state at the Fermi level as a dominant parameter.

Nuclear magnetic resonance features of low-permeability reservoirs with complex wettability

The nuclear magnetic resonance T2 spectra of low-permeability reservoirs with complex wettability were studied using the samples from the Chang 8 Member, Upper Triassic Yanchang Formation, Ordos Basin, China. Abnormally high resistivity and normal resistivity core samples were selected. NMR T2 spectra under different wettability and water saturation conditions, contact angles and Amott wettability indexes were designed and tested. The test results show that under fully brine-saturated condition, the NMR T2 spectra of normal resistivity core samples reflect surface relaxation of water, while the samples with abnormally high resistivity exhibit wide unimodal T2 spectrum, consisting of both surface and volume relaxation of water, which indicates that these cores are not fully water-wet after washing oil. In the process of oil displacing water, the NMR T2 spectra of normal resistivity core samples present bimodal feature, and those of abnormal high resistivity core samples (both non-ageing and ageing) mainly show the same unimodal feature as those measured under fully brine-saturated condition. Based on these results, it can be inferred that the wettability change of abnormally high resistivity core samples to oil-wet has basically completed during oil displacing water process, and the ageing process has little effect on the wettability of abnormally high resistivity core samples. In the process of water displacing oil to residual oil, the NMR T2 spectra of abnormally high resistivity core samples generally show trimodal feature, among which, the shortest relaxation time spectrum peaks coincide with that under irreducible water saturation condition, the moderate ones reflect surface and volume relaxation of residual oil, and the longest ones reflect surface and volume relaxation of water in large pores.

Improving superconducting properties of YBCO high temperature superconductor by Graphene Oxide doping

In this research, we report the synthesis and characterization of YBa2Cu3O7-δ (YBCO) high temperature superconductor prepared by sol-gel method and doped with Graphene Oxide (GO) in different weight percentages, 0, 0.1, 0.7 and 1 % wt. The x-ray diffraction (XRD) analysis confirms the formation of orthorhombic phase of superconductivity for all the prepared samples. We found that GO doping reduces the crystalline size of the samples. We evaluated the effects of GO doping on the normal state resistivity (ρ), superconducting transition temperature (Tc) and critical current density (Jc). The results show that the GO doping has a positive effect on these properties. Also, the highest Jc is obtained for the 0.7 %wt GO doped YBCO compound that its critical current density is about 15 times more than the Jc of pure one in 0.4 T magnetic field. The scanning electron microscope (SEM) analysis shows that there are better connections between the grains of GO doped samples.

AN EXPERIMENTAL STUDY ON RESISTIVITY AND CONDUCTIVE MECHANISM IN LOW‐PERMEABILITY RESERVOIRS WITH COMPLEX WETTABILITY

AbstractAs the clay film developed in low‐permeability lithologic reservoirs absorbs oil, reservoirs become oil‐wet, which results in abnormally high resistivity oil‐water layers and water layers. Such layers bring great challenges to the identification of oil and water layers. In order to make clear the resistivity response characteristics and conductive mechanism in reservoirs with different wettability, cores were selected in Chang 8 formation, Yanchang group, Upper Triassic, the western Ordos basin of China. Experiments were conducted with these samples to simulate the process of oil displacing water, ageing and water displacing oil. In addition, the contact angles of thin slices after washing oil were also tested. The experimental results show that abnormally high resistivity cores are not completely water‐wet after washing oil. However, the formation factors of abnormally high resistivity cores and normal resistivity cores have little difference. In the process of oil displacing water, the relationship between normal resistivity core resistivity index and water saturation is linear in a log‐log plot, while that of abnormally high resistivity cores is convex. The resistivity of abnormally high resistivity cores remains unchanged during ageing process. Combining the analysis of nuclear magnetic resonance (NMR) T2 spectra under different conditions, it can be inferred that wettability of abnormally high resistivity cores has become less water‐wet after oil displacing water, whereas the ageing process has little effect on the wettability. In the process of water displacing oil, the relation between abnormally high resistivity core resistivity index and water saturation is almost linear, which shows that the conductive structure of rock is not changed. Based on the analyses and discussions of these experimental results, a hydrocarbon accumulation mode and the corresponding conductive mechanism are proposed for low‐permeability reservoirs with complex wettability. It shows that abnormally high resistivity water layers are caused by the destruction of continuous conductive paths under oil‐wet condition. The researches and experiments are of great importance for understanding the conductive mechanism, identifying oil and water layers and evaluating water flooded formations in low‐permeability reservoirs with complex wettability.

Improvement of mechanical performances and characteristics of bulk Bi-2212 materials exposed to Au diffusion and stabilization of durable tetragonal phase by Au

This study centers sensitively on the determination of optimum diffusion annealing temperature (650–850°C) for the electrical, superconducting, crystal structure, and especially mechanical characteristics of Au surface-layered Bi-2212 superconducting materials with the aid of dc electrical resistivity, powder X-ray diffraction and microhardness measurements. The experimental results show that all the characteristic properties (normal state resistivity, critical transition temperatures, degree of broadening, phase fractions, lattice cell parameters, elastic modulus, yield strength, fracture toughness, brittleness index and flexural strength parameters) improve considerably with the increment in the annealing temperature up to 800°C as a consequence of the decreased local structural distortions, lattice strains, disorders, defects and grain boundary interaction problems in the Cu-O2 consecutively stacked layers. After the critical annealing temperature value of 800°C, the parameters immediately recrudesce towards their global minimum points. Similarly, the highest Bi-2223 phase fraction and c-axis length are observed at the 800°C annealing temperature due to the best crystallinity and crystal plane alignments. Additionally, the optimum value strengthens the mechanical durability and ideal flexural strength as a result of the stabilization of durable tetragonal phase. Thus, the presence of Au impurities increases the critical stress value so that the crack-producing flaws and cracks propagation divert or slow down rapidly. On the other hand, the excess temperature value such as 850°C leads to the deleterious effect on the mechanical performances of Au surface-layered Bi-2212 compound because of the increased residual porosity and omnipresent flaws (stress raisers and crack initiation sites). Further, it is at least equally important that the crack propagation or dislocation movement more proceeds through the transgranular regions instead of along the intergranular regions with increasing temperature up to the optimum value beyond which the limited number of operable slip systems enhances noticeably and the intergranular fracture becomes more dominant.

Self-assembled c-axis oriented δ-MoN thin films on Si substrates by chemical solution deposition: Growth, transport and superconducting properties

Abstract Molybdenum nitrides Mo-N are considered as the hardest superconducting metal nitrides, which are usually prepared under high pressure and high temperature to obtain high superconducting transition temperature T c . Here, polycrystalline δ -MoN thin films with self-assembled c -axis orientation are directly deposited onto Si substrates by chemical solution deposition under ambient NH 3 annealing atmosphere without high pressure processing. The prepared δ -MoN/Si thin films show T c higher than 12 K. The normal state resistivity obeys electron-phonon scattering mechanism and can be well fitted by Bloch-Gruneisen expression. The results will provide an effective route to prepare large-area δ -MoN/Si thin films with high T c as well as a guidance to investigate the fundamental properties of polycrystalline δ -MoN thin films.

Enhanced superconductivity in TiO epitaxial thin films

Titanium oxides have many fascinating optical and electrical properties, such as the superconductivity at 2 K in cubic titanium monoxide (TiO) polycrystalline bulk. However, the lack of TiO single crystals or epitaxial films has prevented systematic investigations on its superconductivity. Here, we report the basic superconductivity characterizations of cubic TiO films epitaxially grown on (0001)-oriented α-Al2O3 substrates. The magnetic and electronic transport measurements confirmed that TiO is a type-II superconductor and the recorded high Tc is about 7.4 K. The lower critical field (Hc1) at 1.9 K, the extrapolated upper critical field Hc2(0), and coherence length are about 18 Oe, 13.7 T, and 4.9 nm, respectively. With increasing pressure, the value of Tc shifts to lower temperature while the normal state resistivity increases. Our results on the superconducting TiO films confirm the strategy to achieve higher Tc in the epitaxial films, which may be helpful for finding more superconducting materials in various related systems.

Application of Well Logging Techniques for Identification of Coal Seams: A Case Study of Auranga Coalfield, Latehar District, Jharkhand State, India

Application of well logging techniques comprising density, short normal resistivity, long normal resistivity, resistance, self-potential, natural gamma and calliper logs from five wells in Auranga coal field Jharkhand state India, were (The analysis was) carried out to evaluate the fields coal seams prospect i.e. identify lithology and study physical properties based on log data from the five boreholes. We have been identified from combined signatures of available physical properties logs against coal seams and non-coal litho units. Data was acquired and interpreted by software’s Robertson geologging win logger and Well cad software (Version 6.3) respectively. The coal seams are in between shale or sandstone.

Impact of Fe site Co substitution on superconductivity of Fe1-xCoxSe0.5Te0.5 (x = 0.0 to 0.10): A flux free single crystal study

We report synthesis of Co substitution at Fe site in Fe1-xCoxSe0.5Te0.5 (x=0.0 to 0.10) single crystals via vacuum shield solid state reaction route using flux free method. Single crystal XRD results showed that these crystals grow in (00l) plane i.e., orientation in c-direction. All the crystals possess tetragonal structure having P4/nmm space group. Detailed scanning electron microscopy (SEM) images show that the crystals are grown in slab-like morphology. The EDAX results revealed the final elemental composition to be near stoichiometric. Powder X-Ray diffraction (PXRD) Rietveld analysis results show that (00l) peaks are shifted towards higher angle with increasing Co concentration. Both a and c lattice parameters decrease with increasing Co concentration in Fe1-xCoxSe0.5Te0.5 (x=0.0 to 0.10) single crystals. Low temperature transport and magnetic measurements show that the superconducting transition temperature (Tc), decreases from around 12K to 10K and 4K for x=0.03 and x=0.05 respectively. For x=0.10 crystal superconductivity is not observed down to 2K. Electrical resistivity measurement of Fe0.97Co0.03Se0.5Te0.5 single crystal under magnetic field up to 14Tesla for H//ab and H//c clearly showed the anisotropy nature of superconductivity in these crystals. The upper critical field Hc2(0), being calculated using conventional one band Werthamer–Helfand–Hohenberg (WHH) equation, for x=0.03 crystal comes around 70Tesla, 45Tesla and 35Tesla for normal state resistivity criterion ρn=90%, 50% and 10% criterion respectively for H//c and around 100Tesla, 75Tesla and 60Tesla respectively for H//ab. The activation energy of Fe0.97Co0.03Se0.5Te0.5 single crystal is calculated with the help of TAFF model for both H//c and H//ab direction. In conclusion, Co substitution at Fe site in Fe1-xCoxSe0.5Te0.5 suppresses superconductivity.

Hydrostatic pressure effect on the superconducting properties of BaBi3 and SrBi3 single crystals

We demonstrate the superconducting properties of, and hydrostatic pressure effect on, BaBi3 and SrBi3 superconductors. We measure the dc magnetic susceptibility under hydrostatic pressure for both compounds, which shows a positive pressure coefficient of dTc/dP = 1.22 K GPa−1 for BaBi3 and a negative pressure coefficient of dTc/dP = −0.43 K GPa−1 for SrBi3. The normal state electrical resistivity shows that both compounds are highly metallic in nature. The upper critical fields Hc2 evaluated by resistivity under magnetic fields ρ(T,H) are 22 kOe for BaBi3 and 2.9 kOe for SrBi3. A specific heat jump of ΔCe/γTc = 1.05 suggests weak coupling superconductivity in BaBi3, whereas ΔCe/γTc = 2.08 for SrBi3 is higher than the Bardeen–Cooper–Schrieffer theory value of 1.43, indicating a strong coupling superconductor.

The effects of disorder on the normal state and superconducting properties of Nb3Sn

The effect of disorder on the normal state resistivity and the superconducting properties of NbSn is explored in a combination of ab initio calculations and microscopic theory. The crystal symmetry is calculated to be preferentially tetragonal at a normal state resistivity below 27.0 ± 1.4 , and preferentially cubic above this value, which is shown to be consistent with the experimentally observed transition point. The phonon density of states, the Eliashberg spectrum , the electron–phonon coupling constant, the characteristic frequency, the critical temperature Tc, and the upper critical magnetic field at 0 K are calculated over a large normal state resistivity range and shown to be consistent with experimental observations. The high degree of consistency between the calculation results and experimental observations is a strong indication that the calculation approach utilized here, a combination of ab initio calculations and microscopic theory, is a useful tool for understanding the superconducting and normal state properties of NbSn.

Effect of the eccentricity of normal resistivity borehole tools on the current field and resistivity measurement

Three-dimensional finite element numerical model calculations have been carried out to investigate the quantitative effect of the eccentric position of a normal resistivity borehole probe used in practice. Detailed calculations were done between the point-wise analytical solution and numerical solution to verify the results obtained from the finite element method for a normal probe with finite-length cylindrical electrodes. In the borehole the pattern of the current flowing out from current electrode A is efficiently influenced by the eccentricity. For high-resistivity rock the current density is decreased, while for low-resistivity rock it is increased toward the wall side. On the other hand, the eccentricity does not affect considerably the apparent resistivity calculated from electrode potentials. In most geological situations the deviation is less than 2%. However, in infrequent cases when the true resistivity of the rock is extremely low and/or the distance between the potential and current electrodes is very small the effect of the eccentricity can exceed even 10%.

Behavior of Second Generation HighTemperature Superconductor Tapes in Fault Current Limiting Systems

Optimization of high-temperature superconductor (HTS) coated conductor for standalone superconductor fault current limiting (FCL) systems and for inherently fault current limiting cables is quite different. To minimize the amount of conductor, and so to lower cost, a high conductor critical current per unit width Ic,w is desirable to minimize the number of parallel conductors required to meet operating current requirements. In standalone systems, a high normal state resistivity and thin conductor are also desirable to minimize conductor length. But in FCL cables, conductor length is fixed by the application. Limits on Ic,w, resistivity, and thickness also come from the necessity to prevent local overheating during a fault or, in a cable, bubbling of liquid nitrogen which could precipitate a dielectric failure. A critical insight is that even for low-voltage faults, hot spots can arise in the conductor, and heating within these hot spots must also be controlled. A simple model is introduced to describe this phenomenon and estimate hot-spot heating. Tolerable hot-spot temperature rise in FCL cables is drastically less than in standalone FCLs. Implications for design of FCL cables are discussed and their viability for applications such as linking substations at the distribution level is demonstrated.

Effect of CuO2 planes on the structural and superconducting transport properties of [CuTl − 12(n − 1)n;n = 2,3,4] superconductor family

[Formula: see text] [Formula: see text] superconducting bulk samples have been synthesized by using two-step solid state reaction method. We investigated the effects of [Formula: see text] planes on the structural and superconducting transport properties of [Formula: see text] superconducting family. These samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) absorption spectroscopy and DC-resistivity [Formula: see text] measurements. These samples are [Formula: see text]-axis length oriented and have shown orthorhombic crystal structure. All the samples have shown metallic variations of resistivity from room temperature down to onset of superconductivity. The zero resistivity critical temperature [Formula: see text] increases with the increase in superconducting planes and normal state resistivity systematically decreases, which show the density of inadvertent defects decreases in the final compound. The apical oxygen phonon modes are hardened as observed in the FTIR absorption measurements. The intrinsic microscopic superconducting parameters, such as the cross-over temperatures, coherence length along [Formula: see text]-axis [Formula: see text] at 0 K, inter-layer coupling [Formula: see text], inter-grain coupling [Formula: see text] and fermi velocity [Formula: see text], were extracted from the fluctuation-induced conductivity (FIC) analysis. FIC analysis also showed the improvement in superconductivity with the increase in [Formula: see text] planes.