Behavior Of Tc Research Articles

Correlation between Tc and local structure of MgB2 with ZnO buffer layer: X-ray absorption fine structure study

In practical application, it is necessary to preserve the superconducting properties, including the critical temperature (Tc) of MgB2 in the form of tapes and wires that bond to a metallic substrate with a buffer layer. In this work, we investigate the relationship between the Tc and local structure of MgB2 films on ZnO buffered-Hastelloy substrate with various thicknesses using X-ray absorption fine structure. X-ray absorption near edge structure spectra reveal fluctuation of the boron σ-band near the Fermi level indicating an existence of lattice distortion inside the MgB2 films. Variations in the bond lengths of Mg–B and Mg–Mg from the extended X-ray absorption fine structure prove that the distortion in the MgB2 lattice is owing to the ZnO buffer layer. Besides the bond length, the Mg–B bond ordering was found to significantly affect the Tc behavior, which was attributed to the inter-plane strain caused by the ZnO buffer layer. Understanding the effect of the ZnO buffer layer on the local structure of MgB2 may help in determining the optimal conditions for enhancing the superconducting properties of MgB2 for power applications.

Rapid determination of 99Tc in water samples using Ti(OH)3-TcO2 co-precipitation and TK200 resin by liquid scintillation counting

A novel method for the determination of 99Tc in water samples was developed using stable Re as a chemical yield tracer and TiCl3 as a reducing agent. The influences of several experimental parameters, including TiCl3 concentration, HCl concentration and reaction time, on the reduction of TcO4− and ReO4− as well as Ti(OH)3-TcO2-ReO2 co-precipitation were investigated. Tc(VII) and Re(VII) retained on TK200 resin were effectively eluted by 5 mL of 1 mol/L NH4SCN, which can be directly mixed with the scintillation cocktail for liquid scintillation counting. The results show that the chemical behaviors of Tc and Re are very consistent in the whole procedure. The decontamination factors of potential interferences from β-emitting nuclides mainly released from nuclear fuel reprocessing plants were also evaluated, and the minimum detectable activity concentration was calculated to be 0.08 Bq/L for 99Tc in water samples with a counting time of 2 h.

Investigation of effective parameters on relative thermal conductivity of SWCNT (15%)-Fe3O4 (85%)/water hybrid ferro-nanofluid and presenting a new correlation with response surface methodology

In this study, the parameters affecting the relative thermal conductivity (RTC) of SWCNT (15%)-Fe3O4 (85%)/Water Hybrid Ferro-Nanofluid (HFNF) are investigated. The contributions of temperature and the solid volume fraction (SVF) are carefully studied and analyzed. The initial increase of TC of produced HFNF relative to water at SVF = 0.03% and T = 30 °C is equal to 0.9%, but the maximum amount of RTC is reported to be 32.20%, which is a significant amount. The contribution of each parameter in increasing the RTC is considered in present sutdy. In this study, in addition to the laboratory study the response surface methodology (RSM) is used as mathematical based method to predict the TC behavior of studied HFNF and after that, the MOD and sensitivity of RTC are applied to check the accuracy f predictions. As the result of the RSM a new correlation with R2 = 0.9941 is also predicted for the studied HFNF and as another result the highest RTC sensitivity is reported at + 1.58%.

Critical Temperature in the BCS-BEC Crossover with Spin-Orbit Coupling

We review the study of the superfluid phase transition in a system of fermions whose interaction can be tuned continuously along the crossover from Bardeen–Cooper–Schrieffer (BCS) superconducting phase to a Bose–Einstein condensate (BEC), also in the presence of a spin–orbit coupling. Below a critical temperature the system is characterized by an order parameter. Generally a mean field approximation cannot reproduce the correct behavior of the critical temperature Tc over the whole crossover. We analyze the crucial role of quantum fluctuations beyond the mean-field approach useful to find Tc along the crossover in the presence of a spin–orbit coupling, within a path integral approach. A formal and detailed derivation for the set of equations useful to derive Tc is performed in the presence of Rashba, Dresselhaus and Zeeman couplings. In particular in the case of only Rashba coupling, for which the spin–orbit effects are more relevant, the two-body bound state exists for any value of the interaction, namely in the full crossover. As a result the effective masses of the emerging bosonic excitations are finite also in the BCS regime.

Transition metal solutes in Ni-based ternary model superalloys: Partitioning and effects on elastic properties from first-principles calculations

Alloying effects on the structural, elastic, as well as electronic properties of Ni-based model superalloys are systematically investigated by first-principles calculations. Twenty-seven transition-metal(TM) elements (3d:Sc-Zn, 4d:Y-Cd, 5d:Hf-Au) are taken into account in Ni-based ternary model superalloys in detail for the first time. The partitioning behaviors and site preferences of ternary alloying elements are primarily predicted based on our calculated substitutional formation energies and partitioning coefficients, with previous atom probe tomography(APT) experimental results for comparison. Temperature dependence of partitioning behaviors of TM elements in model superalloys is also presented in this work. It is found that the partitioning behaviors of Cr, Mn, Tc, Ru and Os can be reversed at a specific temperature, and these elements just lie near the boundary between the two blocks of Ni-site preferences and Al-site preferences of TM elements on the periodic table. The bulk moduli, Young’s moduli, shear moduli, ductile–brittle behavior, orientation-dependent elastic moduli and elastic anisotropy of Ni-based ternary model superalloys are systematically estimated. The calculated elastic parameters agree well with the available experimental results. The effects of TM elements on elastic properties are found to be closely associated with their d-electron number. The elements at the beginnings and ends of the TM series reduce these elastic properties, while the TM elements lying towards the center of each period can considerably increase these properties of superalloys, especially those elements with a half-filled d band, which exert greater influences on improving the elastic performance. Furthermore, different charge redistributions caused by each alloying addition can elucidate different effects thereof on the elastic properties of model superalloys to some extent. The stronger directional bonding and more covalent-like interaction between TM additions and host atoms lead to the superior elastic properties.

Controlled electron transmission by lead chalcogenide barrier potential

Transmission of electrons across a rectangular barrier of IV–VI semiconductor compounds is considered. Conduction electrons arrive at the barrier and are reflected or transmitted through it depending on the relative values of the barrier potential V b and the electron energy E. The theory, in close analogy to the Dirac four component spinors, accounts for the boundary conditions on both sides of the barrier. The calculated transmission coefficient TC is an oscillatory function of the barrier voltage varying between zero (for full electron reflection) and unity (for full electron transmission). Character of electron wave functions outside and inside the barrier is studied. There exists a total current conservation, i.e. the sum of transmitted and reflected currents is equal to the incoming current. The transmission TC is studied for various barrier widths and incoming electron energies. Finally, the transmission coefficient TC is studied as a function of V b for decreasing energy gaps E g of different Pb1 − x Sn x Se compounds in the range of 150 meV 2 meV. It is indicated that for very small gap values the behavior of TC closely resembles that of the chiral electron tunneling by a barrier in monolayer graphene. For E g = 0 (Pb0.81Sn0.19Se) the coefficient TC reaches the value of 1 independently of V b .

Local structure and superconductivity in (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1-x(Fe3O4)x compounds

In this work, a close correlation between variations of critical temperature (Tc) and the hole concentration of (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1-x(Fe3O4)x systems was studied. The (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1-x(Fe3O4)x samples were fabricated using the solid-state reaction method, where x ranged from 0 to 0.2. The Tc values of the samples deduced from magnetization versus temperature measurement gradually decreased with increasing the Fe3O4 content (x). To investigate a possible reason for the observed decrease in the values of Tc in the samples, the valence state of copper (V) and the hole concentration (p) in all samples were examined by analyzing the Cu K-edge and Cu L2,3-edge X-ray absorption near edge structure (XANES) spectra. The values of V and p monotonously decreased with the increase in Fe3O4 doping content (x) and agreed with the behavior of Tc. The existence of Fe3+ was confirmed by analyzing Fe L2,3-edge XANES. Hence, Fe3+ ions possibly entered the lattice structure of the samples and filled the holes in CuO2 planes. The degradation of superconductivity in Fe3O4 doped samples was then explained.

Enhancing Superconductivity of the Nonmagnetic Quasiskutterudites by Atomic Disorder.

We investigated the effect of enhancement of superconducting transition temperature by nonmagnetic atom disorder in the series of filled skutterudite-related compounds (LaSn, CaRhSn, YRhSn, LuRhSn; Co, Ru, Rh), where the atomic disorder is generated by various defects or doping. We have shown that the disorder on the coherence length scale in these nonmagnetic quasiskutterudite superconductors additionally generates a non-homogeneous, high-temperature superconducting phase with (dilute disorder scenario), while the strong fluctuations of stoichiometry due to increasing doping can rapidly increase the superconducting transition temperature of the sample even to the value of (dense disorder leading to strong inhomogeneity). This phenomenon seems to be characteristic of high-temperature superconductors and superconducting heavy fermions, and recently have received renewed attention. We experimentally documented the stronger lattice stiffening of the inhomogeneous superconducting phase in respect to the bulk one and proposed a model that explains the behavior in the series of nonmagnetic skutterudite-related compounds.

Magnetic doping effects on the superconductivity of Y1-xMxBa2Cu3O7-δ (M = Fe, Co, Ni)

The discovery of superconductivity in copper oxide compounds has attracted considerable attention over the past three decades. The high transition temperature (Tc) in these compounds, exhibiting proximity to an antiferromagnetic order in their phase diagrams, remains one of the main areas of research. It is believed that magnetic fluctuations provide substance for the exotic superconductivity observed in these compounds. The present study attempts to introduce Fe, Co and Ni magnetic impurities into the superconducting cuprate YBa2Cu3O7-δ with the aim of exploring the Tc behavior. The solid-state synthesis method is exploited to prepare fully oxygenated Y1-xMxBa2Cu3O7-δ (Y1-xMx-123) (M = Co, Fe, Ni) samples with low levels of doping (0.00000 ≤ x ≤ 0.03000). Systematic measurements are then employed to assess the synthesized samples using AC magnetic susceptibility, electrical resistivity and X-ray diffraction (XRD). The measurements revealed an increase in Tc as a result of magnetic substitution for Y. However, the study of non-magnetic dopings on the fully oxygenated Y1-xM'xBa2Cu3O7-δ (Y1-xM'x-123) (M' = Ca, Sr) samples showed a decrease in Tc. Quantitative XRD analysis further suggested that the internal pressure could have minor effects on the increase in Tc. The normal state resistivity vs temperature showed a linear profile, confirming that the samples are at an optimal doping of the carrier concentration.

Electron-phonon coupling behavior in MgB2 films with various thicknesses of ZnO buffer layer on metallic substrates

In order to investigate the effect of buffer layer on the superconducting properties of MgB2, behaviors of electron-phonon coupling (EPC) in MgB2 thin films with various thicknesses of ZnO buffer layer on two different substrates Al2O3 and Hastelloy were studied. As the ZnO thickness increases, the values of Tc of MgB2 films on two substrates show opposite behaviors. Sharply decreased and then saturated Tc of ~38K is observed on Al2O3 substrates while an abrupt increase of Tc with no tendency of decrease is obtained on Hastelloy substrates. These Tc behaviors are closely related to the E2g phonon hardening/softening inside MgB2 which may be induced from a lattice distortion caused by an introduction of ZnO buffer layer. The electron-E2g coupling provides a dominant contribution to EPC from all phonon modes, however, it shows a very weak dependence on ZnO thickness to explain the Tc behavior of our samples. Therefore, in order to establish a mechanism of ZnO buffer layer influencing Tc of MgB2 films, contribution from other phonon modes needs to be considered. Understanding the effect of ZnO buffer layer on the EPC and the Tc behavior opens a possibility to obtain an optimal condition for ZnO buffer layer of MgB2 for the field of application.

Melt density, equilibrium melting temperature, and crystallization characteristics of highly pure cyclic poly(ε-Caprolactone)s

A series of cyclic and linear poly (ε-caprolactone)s (c-PCLs: c-PCLn, n = 30–200, average degree of polymerization; l-PCLs: l-PCLn, n = 30–200) in extremely high purity have been quantitatively investigated in terms of melt density, equilibrium melting temperature crystallization nature in connection to molecular topology effects. Synchrotron X-ray reflectivity analysis determined higher melt densities for c-PCLs than those of the linear counterparts. c-PCL was determined to exhibit 8.4 °C higher equilibrium melting temperature than that of the linear counterpart. Such higher equilibrium melting temperature may originate from a cooperative effort of thermodynamic factors (larger equilibrium heat of fusion and smaller equilibrium entropy) and morphological factors (thicker crystalline layer and higher fold surface energy). Comparing with l-PCL, c-PCL revealed apparently faster crystallization behavior at a chosen Tc but slower crystallization behavior at a same degree of supercooling because of the higher equilibrium melting temperature. Both c-PCL and linear counterpart were observed to follow heterogeneous nucleation and growth mechanism in crystallizations. Overall, this study achieved comprehensive insights into cyclic topology effects on the melt density, equilibrium temperature, and crystallization behavior of PCL.

Enhancement of Coherence Length and Nonlinear Current-Voltage (IV) Characteristics of Ag-Doped GBCO

The resistivity as a function of temperature of GdBa2Cu3-xAgxO7-δ superconductors reveals that the critical temperature, Tc, increases with the concentration of Ag (x). An equation has been suggested to understand the behaviour of Tc (x). The coherence length has been extracted on the basis of the three dimensional Aslamazov-Larkin (3DAL) equation to understand the enhancement in the critical temperature. We have studied current-voltage (IV) curves below Tc to understand the nonlinearity observed in doped samples. An exponent has been extracted to explore the possibility of Kosterlitz-Thouless (KT) transition and the role of the coherence length in the nonlinear behaviour.

Chemically modified biochar derived from effluent treatment plant sludge of a distillery for the removal of an emerging pollutant, tetracycline, from aqueous solution

Distilleries are among the most pollution-generating industries as their ≈80% raw material converted into waste. In the present study, sustainable biochar was prepared from distillery sludge (DS) by chemical activation with KOH, ZnCl2, and H3PO4 (coded as DS-K, DS-Z, DS-H) and used for the removal of tetracycline, an emerging pollutant. Additionally, biochar was also prepared by adding the distillery sludge and oily sludge from sugar mill in the ratio of 2:1 (coded as DS-O). The raw sludge and prepared biochar were characterized by various sophisticated techniques like XRF, XRD, TGA-FTIR, BET, FE-SEM, and zeta potential analyzer. FTIR, coupled with the TGA system, gave traces of CO2 and H2O (steam) as the temperature of the sample increased. Batch adsorption study showed TC removal efficiencies of 57%, 64%, 43%, and 70% by DS-K, DS-Z, DS-H, and DS-O, respectively, at optimum conditions: Co = 20 mg L−1, time = 300 min, rpm = 160 ± 5, dose = 1 g L−1, T = 25 ±1 °C, and pH = 6. Experimental data was well-fitted in both pseudo-first-order and pseudo-second-order kinetic models. Langmuir isotherm nicely described the adsorption of TC onto biochar. pH played a significant role in the adsorption due to the amphoteric behavior of TC. Reusability studies showed a marginal decrease in removal efficiencies of ≈ 9%, ≈ 7%, ≈ 4%, and ≈ 8% after three consecutive runs with DS-O, DS-Z, DS-K, and DS-H, respectively.

Self-Doping Effect in FeSe Superconductor by Pressure-Induced Charge Transfer

Several unambiguous experimental observations clearly showed that the critical temperature of FeSe superconductor depends significantly on the microstructure. Experiments also showed that the critical temperature can be greatly enhanced by the application of external pressure. The present paper deals with the effect of pressure on charge transfer and self-doping properties of the superconducting compound FeSe, based on the investigation of the pressure dependence of the Fermi surface by means of first-principles methods. From the numerically evaluated electronic and crystalline properties, the pressure-induced modifications of the FeSe Fermi surface’s topology are determined. The Luttinger theorem was also used to evaluate the carrier concentration on the Fe atomic sites from the evolution of the Fermi surface. We have found that the electronic density at the Fe sites increases with the increase in external pressure, following the distortion of Fermi surface. Our simulations reveal that the pressure-induced charge transfer from Se atoms to Fe atoms in the FeSe superconductor can be interpreted as a direct correlation between the electron carrier concentration and the applied pressure. The pressure dependence of superconducting properties of FeSe can be reasonably ascribed to a self-doping effect. The predictions about the electronic density on the Fe sites (reaching a value of 0.1, where the corresponding pressure is about 8.6 GPa) are in good agreement with experimental data available in literature. The interpretation of the pressure-induced Tc enhancement in FeSe caused by the electron transfer and self-doping effect is carried out, which can be the correct approach to explain the Tc behavior under a wide type of mechanical loading.

Tc behavior and influence in U/Pu partition flowsheet experiments with organic reducing agents

Tc play an important role in U/Pu partition when U(IV) is used as reducing agent in PUREX process. In this work, U/Pu partition flowsheet experiments were studied using different organic reducing agents, which included N,N-dimethylhydroxylamine (DMHAN)–methylhydrazine (MMH), acetohydroxamic acid (AHA) and dihydroxyurea (DHU). The results showed very good U/Pu partition performance in the presence of Tc, which mean Tc would not cause major malfunctions in the U/Pu partition operation with these reducing agents. The technetium fractions distributed in the products was mainly attributed to Tc(VII) reduction kinetics with different reducing agents.

Convenient method for Curie temperature determination in holmium and yttrium manganite based on capacitance value

This study reported an alternative technique to measure the Curie temperature (Tc) of hexagonal manganite as multiferroic sample. The method is based on change identification in slope of capacitance value as a function of temperature. Temperature variation of the capacitance observed in holmium and yttrium manganite sintered at 1250 °C has been studied respectively. The optimum preparation of holmium and yttrium manganite with space group P63cm by using high energy ball milling has been chosen in order to provide a convenient Tc. The changes of the capacitance value as a function of temperature range from 300 up to 1000 K at 50 Hz has been carried out in order to obtained the Tc value. Results obtained from the experiments showed that Tc transition could be clearly exhibited by the capacitance value for both the holmium manganite and yttrium manganite samples. The measured property values gave their Tc transition around reported value in previous studies. The ferroelectric Tc transition was observed to be 850 K and 860 K for HoMnO3 and YMnO3 respectively. A completely intrinsic behaviour of Tc was revealed by our simple and low cost method since no applied external field was used, yielding a truly spontaneous ferroelectric behaviour.

Exploring the Proximity Effect in Mo/Au Bilayers

We report on the sensitivity of superconducting transition temperature (Tc) to the individual layers' thickness in Mo/Au proximity bilayers to be used in transition-edge sensors (TESs). The achieved good reproducibility and quality of the bilayers allow a clear determination of the superconducting critical temperature Tc as a function of the Mo and Au thicknesses. One objective of this work is to analyse the quality of the Mo/Au interface and to assess the possible effects of the double Au layer we use to fabricate these bilayers and TESs based on them. Experimental data are analysed on the basis of Usadel equations using the model developed by Martinis and co-workers, in which the proximity effect in the bilayer is mainly governed by the interface transparency between the superconductor and the normal metal. We find that this model describes quite well the behavior of Tc, even for quite thick Au layers, and that the double Au layer does not play any relevant role on the proximity effect.

Effect of K Substitution on Local Structure of Bi1.6Pb0.4Sr2−xKxCa2Cu3O10+δ System Probed by Extended X-Ray Absorption Fine Structure

The effect of K substitution on the local atomic structure of polycrystalline Bi1.6Pb0.4Sr2−xKxCa2Cu3O10+δ samples (BSCCO, x = 0, 0.02, 0.06, and 0.10) has been investigated. Unlike in other cases of alkaline substitution, the transition temperature Tc of the K-substituted BSCCO samples decreased systematically with increasing K content. Such decreasing Tc behavior supposedly originates from changes in the local structure of the BSCCO system. Analysis of extended x-ray absorption fine structure (EXAFS) data measured at both the Cu K-edge and Sr K-edge revealed that, as the K content was increased, the Cu–O and Cu–Sr bonds systematically extended, while the Sr–O bond distance gradually reduced. The corresponding mean-square relative displacement (MSRD), which represents the average local distortion, showed large alteration in both the CuO2 and SrO planes. Local atomic displacement due to K substitution seemed to weaken the interaction between the conduction layer and spacer layer, resulting in a drastic decrease of the Tc values. Overall, these experimental results provide important information to understand the correlation between the superconductivity and local structure of K-substituted BSCCO.

Structure, morphology, infra-red and dielectric investigations in Er+3 doped nano phased lithium-barium-strontium-sodium niobates

Synthesis of nano phased Er+3 doped (x) Li optimized Barium Strontium Sodium Niobates (BSNN), viz.,Ba1.6-(3x/2)Sr2.4Na1.4Li0.6ErxNb10O30 by co-precipitation method reported. XRD confirmed orthorhombic structure. Lattice parameter ‘b’ exhibited anomaly for x ≥ 0.8. Orthorhombic Cmm2 and Ccm21 symmetries predict Ferro or Piezo and Pyro response. (401) for x = 0.9; and (401) and (801) for x = 1 reflection and split infer Ccm21 symmetry and lower ordered Cmm2 structure along diad axis in [001] direction. Absence of additional (hol) reflections for h-even and l-odd are addressed. Crystallite size D(x) exhibited anomaly for x around 0.9. Particle size and Porosity P(x) by FESEM and Density ρ(x) inferred systematic growth of ferroelectric(FE) phase. Anomaly in D is attributed to distinct dopant characteristic nucleation. Cluster population of 10–20 nm size prevail over entire dopant range. Concurrent behavior of D and P with x is observed. Low frequency (100 KHz) Dielectric permittivity inferred shift of Curie temperature Tc for ambiance. Large permittivity (K) is observed for 0 ≤ x ≤ 0.2. Decrease of K with P confirms growth of nano phase from bulk morphology. Decrease in K with P infers morphology influence field response. Trends of K with x infers shift of Tc (x) with an anomaly for x equal to 0.9. influence of D and P analyzed. FE transition progressively gets diffused with increasing x or decrease in D (∼30–20 nm) and P (for 45–25 nm). Critical analysis of nano phased Er doped Li BSNNs reveals growth of localized stress contributing to excess free volume of grain boundaries. Incongruent behavior of Tc discussed. Trends of axial ratio (AR), dielectric permittivity and Tc are analyzed in comparison with the reports in other systems of relevance.

Transition temperature enhancement of nano-structured superconductors: Shape dependence and effects of Cooper pair distribution

Enhancement of superconducting critical temperature Tc for nano-structured square and rectangular plates is investigated, using the Gor’kov equations and the finite element method. Tc increases with decreasing system size and shows sawtooth behavior as the function of system size. We find the enhancement of Tc becomes larger for narrower rectangular plate. We discuss mechanisms of these behaviors of Tc, investigating quasi-particle eigen-energies and spatial order parameter distributions.