Critical Transition Temperature Research Articles

The Critical Temperature of Superconducting Aluminum Films

The R(T) dependences of thin superconducting aluminum films deposited on leucosapphire and gallium arsenide substrates by electron beam sputtering and molecular beam epitaxy have been experimen-tally studied. Regardless of morphology, a noticeable increase in the critical temperature of the supercon-ducting transition with a decrease in the film thickness is found. The effect is interpreted as a manifestation of the quantum size effect.

Computer simulation and machine learning of polymer collapse and critical adsorption phase transitions

Collapse and critical adsorption of polymers are two crucial phase transitions in polymer science, both are accompanied by significant changes in polymer conformation. In this paper, Langevin dynamics and dynamic Monte Carlo methods are used to simulate the collapse and critical adsorption of polymer, respectively, and corresponding phase transition temperatures are estimated. Meanwhile, a large number of polymer conformations at different temperatures are obtained. In the machine learning method, a large number of extended random coil and collapsed spherical, desorption and adsorption conformations are used to train the neural network, so that the neural network can learn the characteristics of different states of the polymer, and it can quickly and accurately analyze the polymer conformations at different temperatures and obtain the corresponding collapse phase transition temperature and critical adsorption temperature. The results demonstrate that machine learning can correctly calculate the phase transition temperature of polymer system, which provides new ideas and methods for machine learning technology in the study of polymer phase transitions.

Analysis of fluctuation conductivity in Y-=SUB=-0.5-=/SUB=-Cd-=SUB=-0.5-=/SUB=-Ba-=SUB=-2-=/SUB=-Cu-=SUB=-3-=/SUB=-O-=SUB=-7-delta-=/SUB=-

A study was made of the influence of substitution of up to 50% of yttrium for cadmium in YBa2Cu3O7-delta polycrystals on the mechanism of formation of excess conductivity. It has been established that such a substitution led to a significant increase in the resistivity of Y0.5Cd0.5Ba2Cu3O7-delta, and the value of the critical transition temperature Tc to the superconducting state decreases. The mechanism of formation of fluctuation conductivity (T) near Tc is considered within the framework of the Aslamazov-Larkin theory. The Ginzburg temperature, the critical temperature in the mean field approximation, and the 3D-2D crossover temperature were determined. It is shown that the doping of YBa YBa2Cu3O7-delta with cadmium leads to an increase in the coherence length along the c axis by a factor of 3.2. An analysis of the excess conductivity of the Y0.5Cd0.5Ba2Cu3O7-delta sample within the framework of the local pair model made it possible to determine the temperature dependences of the pseudogap and its maximum value. Keywords: superconductivity, fluctuation conductivity, pseudo-gap, coherence length.

Two-dimensional superconducting nature of Bi2Sr2CaCu2O8+δ thin films revealed by BKT transition.

High-quality Bi2Sr2CaCu2O8+δ superconducting thin films are successfully grown on a SrTiO3 substrate by the Pulsed Laser Deposition technique. Superconducting critical transition temperatures Tc,zero have reached up to 85 K by using optimized growth parameters. In addition, we demonstrated the two-dimensional nature of the superconductivity of thin films by virtue of exhibiting Berezinskii-Kosterlitz-Thouless (BKT) physics and anisotropic magnetic response. Furthermore, three distinct regimes are identified based on the analysis of direct current resistance. The non-Fermi liquid phase and BKT phase fluctuation zone almost perfectly merge together, which implies that the system undergoes a unique topological state that is determined by the BKT phase fluctuation preceding the onset of the superconducting state. The emergence of such a topological state radically differentiates from the three-dimensional superconducting transition, which spontaneously breaks the gauge symmetry. The current studies on the Bi2Sr2CaCu2O8+δ superconducting thin films provide some new insights for understanding the rich quantum states of matter that emerge in the vicinity of the superconducting phase transition and highlight the significant role of BKT fluctuation on two-dimensional superconducting transition.

Magnetron technology for preparation of tape superconductors with Nb3Ge coating

Modern experimental facilities require new types of superconducting materials. The intermetallic compound with the A15 Nb3Ge structure is known as the most perspective material for large superconducting magnets.The article provides a detailed description of the features used in the experimental setup capable of producing intermetallide Nb3Ge in the form of coatings on a long copper tape. The structure of the formed coatings has been studied and the critical transition temperature has been determined. The stability of the proposed technology has been shown in relation to such harmful factors as the insufficient purity of the feedstock and presence of oil vapor in the vacuum.

On the thermal and mechanical properties of Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O across the high-entropy to entropy-stabilized transition

As various property studies continue to emerge on high entropy and entropy-stabilized ceramics, we seek a further understanding of the property changes across the phase boundary between “high-entropy” and “entropy-stabilized” phases. The thermal and mechanical properties of bulk ceramic entropy stabilized oxide composition Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O are investigated across this critical transition temperature via the transient plane-source method, temperature-dependent x-ray diffraction, and nano-indentation. The thermal conductivity remains constant within uncertainty across the multi-to-single phase transition at a value of ≈2.5 W/mK, while the linear coefficient of thermal expansion increases nearly 24% from 10.8 to 14.1 × 10−6 K−1. Mechanical softening is also observed across the transition.

Investigating the critical transitional temperature increase in graphene oxide doped bulk YBCO

Y1Ba2Cu3O7-δ (YBCO) was doped with thermally stable graphene oxide (TS-GO) and thermally unstable graphene oxide (TU-GO) in the following %wt. concentrations: 0.1, 0.5 and 0.7. TS-GO and TU-GO was characterized using RAMAN, fourier transform infrared spectroscopy (FTIR) and energy-dispersive X-ray spectroscopy (EDX). The critical transition temperature (TCmid) increased in all TU-GO and TS-GO doped samples. The highest TCmid of 101 K was that of the 0.7 %wt. TU-GO doped sample. The increase in TCmid was greater for the samples doped with TU-GO. Non-stoichiometric oxygen content (δ) was seen to increase with an increase in doping concentration of both TS-GO and TU-GO. X-ray diffraction (XRD) analysis was carried out to determine the lattice parameters and phase characterization of the TU-GO and TS-GO doped samples. Lattice parameters show an increase in the copper oxide (CuO2) planar area with TCmid for TS-GO and TU-GO doping. To determine strain effects, the Williamson Hall method was used to determine the lattice strain (ɛ). The ɛ was seen to decrease for both TS-GO and TU-GO doped samples. The formation of magnetic manganese oxide nanoparticles in TS-GO and TU-GO doped samples was observed, and resulted from impurities found in the graphene oxide (GO) dopant material. The magnetic particles were extracted magnetically and characterized using EDX. YBCO was doped with trimanganese tetraoxide (Mn3O4) and manganese dioxide (MnO2) in a 0.1 and 0.2 %wt. concentration. The TCmid is seen to increase to 94 K and 104 K respectively for 0.1 %wt. MnO2 and Mn3O4 doped samples. The 0.2 %wt. doped Mn3O4 sample resulted in a decrease in TCmid. Magnetic susceptibility measurements confirmed a superconducting phase changes. The increase in TCmid above YBCO’s Tc = 93 K, correlates to the presence of manganese nano-impurities. This increase is hypothezied to be related to an increase in surface area of YBCO’s 2D copper oxide (CuO2) plane structure with GO doping.

Thermoresponsive Block Copolymer Core-Shell Nanoparticles with Tunable Flow Behavior in Porous Media.

With the purpose of investigating new polymeric materials as potential flow modifiers for their future application in enhanced oil recovery (EOR), a series of amphiphilic poly(di(ethylene glycol) methyl ether methacrylate-co-oligo(ethylene glycol) methyl ether methacrylate) [P(DEGMA-co-OEGMA)]-based core-shell nanoparticles were prepared by aqueous reversible addition-fragmentation chain transfer-mediated polymerization-induced self-assembly. The developed nano-objects were shown to be thermoresponsive, demonstrating a reversible lower-critical solution temperature (LCST)-type phase transition with increasing solution temperature. Characterization of their thermoresponsive nature by variable-temperature UV-vis and dynamic light scattering analyses revealed that these particles reversibly aggregate when heated above their LCST and that the critical transition temperature could be accurately tuned by simply altering the molar ratio of core-forming monomers. Sandpack experiments were conducted to evaluate their pore-blocking performance at low flow rates in a porous medium heated at temperatures above their LCST. This analysis revealed that particles aggregated in the sandpack column and caused pore blockage with a significant reduction in the porous medium permeability. The developed aggregates and the increased pressure generated by the blockage were found to remain stable under the injection of brine and were observed to rapidly dissipate upon reducing the temperature below the LCST of each formulation. Further investigation by double-column sandpack analysis showed that the blockage was able to reform when re-heated and tracked the thermal front. Moreover, the rate of blockage formation was observed to be slower when the LCST of the injected particles was higher. Our investigation is expected to pave the way for the design of "smart" and versatile polymer technologies for EOR applications in future studies.

Direct Observation of the Topological Surface State in the Topological Superconductor 2M-WS2.

The quantum spin Hall (QSH) effect has attracted extensive research interest because of the potential applications in spintronics and quantum computing, which is attributable to two conducting edge channels with opposite spin polarization and the quantized electronic conductance of 2e2/h. Recently, 2M-WS2, a new stable phase of transition metal dichalcogenides with a 2M structure showing a layer configuration identical to that of the monolayer 1T' TMDs, was suggested to be a QSH insulator as well as a superconductor with a critical transition temperature of around 8 K. Here, high-resolution angle-resolved photoemission spectroscopy (ARPES) and spin-resolved ARPES are applied to investigate the electronic and spin structure of the topological surface states (TSS) in the superconducting 2M-WS2. The TSS exhibit characteristic spin-momentum-locking behavior, suggesting the existence of long-sought nontrivial topological states therein. We expect that 2M-WS2 with coexisting superconductivity and TSS might host the promising Majorana bound states.

Clustering in nuclei at finite temperature

We investigate the localization and clustering features in $^{20}$Ne ($N=Z$) and neutron-rich $^{32}$Ne nuclei at zero and finite temperatures. The finite temperature Hartree-Bogoliubov theory is used with the relativistic density-dependent meson-nucleon coupling functional DD-ME2. It is shown that clustering features gradually weaken with increasing temperature and disappear when the shape phase transition occurs. Considering thermal fluctuations in the density profiles, the clustering features vanish at lower temperatures, compared to the case without thermal fluctuations. The effect of the pairing correlations on the nucleon localization and the formation of cluster structures are also studied at finite temperatures. Due to the inclusion of pairing in the calculations, cluster structures are preserved until the critical temperatures for the shape phase transition are reached. Above the critical temperature of the shape phase transition, the clustering features suddenly disappear, which differs from the results without pairing.

Preliminary results on deconfinement phase transition in full QCD

We explore the profiles of the flux tube connecting a quark and an antiquark in hightemperature SU(3) lattice gauge theory in close vicinity to the critical temperature of thephase transition. In this work, we consider the more realistic case of the flux tube withdynamical quarks, extending the previous study to SU(3) gauge group and making use ofthe Gradient flow method in smoothing procedure for noise reduction. The profiles of thechromoelectric and chromomagnetic field strengths in the flux tube have been measuredfrom Polyakov loop-plaquette correlations using the highly improved staggered quark(HISQ) action on a lattice with temporal extent.

Safety analysis of thermal equipment and piping systems in the CANDU nuclear power plant subjected to thermal shocks

Due to the complexity of nuclear power plants and the risks of damage that may occur during their existence, it is necessary to pay more attention to the safety features. An important influence is the operational temperature of thermal equipment and pipes, especially within the primary circuit, as the coolant is radioactive and in case of damage would cause natural disasters. An assessment of thermal reliability of nuclear power plant equipment and systems is necessary for optimization in the design stage. High thermal shocks with severe and sudden drop in coolant temperature represent a high potential for damage, especially in propagation of existing cracks, under stress due to high pressures. On the other hand, vibrations produced by variable fluid flow conditions or of mechanical origin may induce vibratory fatigue, which combined with thermal fatigue may influence the system’s safety. This study aims to develop computational models for thermal fatigue in pipelines in nuclear power plants, highlighting pressurized thermal shock analysis, temperature distribution diagram along the wall thickness, stress distribution diagram by wall thickness, factor distribution diagram stress intensity, critical crack size diagram, critical reference temperature of nil ductility transition (RTNDT) diagram. Evaluation of these diagrams were performed using the calculation programs Nuclear Piping Integrity Expert System (NPIES) and Reactor Vessel Integrity Evaluation System (RVIES).

The Effect of Additives on the Hydrothermal Synthesis and Thermochromic Performance of Monoclinic Vanadium Dioxide Powder

Monoclinic vanadium dioxide VO2(M) is a well-known thermochromic material, with its critical transition temperature (68 °C) being the closest to room temperature (RT). Among the variety of grown methods, hydrothermal synthesis is a simple and cost-effective technique to grow thermochromic VO2 in the form of powder. In the present work, VO2 nanoparticles were prepared by hydrothermal synthesis in mild conditions, followed by a thermal annealing process at 700 °C under nitrogen flow for two hours. Vanadium pentoxide (V2O5) was used as the vanadium precursor, while two different reducing agents, namely oxalic and succinic acid, were employed for the reduction of V2O5 to VO2. Additionally, urea as well as thiourea were used as additives, in order to investigate their effects on the thermochromic performance of VO2. As a result, the VO2 (M) phase was obtained after annealing the crystalline powder, grown hydrothermally using oxalic acid and thiourea as a reducing agent and additive, respectively. This synthesis had a high yield of 90%, and led to a VO2(M) powder of high purity and crystallinity. In particular, the VO2 (M) nanoparticles had an average crystallite size of approximately 45 nm, a critical transition temperature of approximately 68 °C and a hysteresis width of 11 °C.

Recent Advances in Iron-based Superconducting Coated Conductors

The discovery of high-temperature superconductivity in iron-based superconductors (IBSs) as the second class of high-temperature superconducting transition materials after the cuprates has given a considerable impact on fundamental and applied superconductivity research. Due to their superior superconducting properties, including extremely high upper critical fields, small anisotropy, advantageous grain boundary (GB) feature and relatively high critical transition temperatures, numerous studies have been performed to understand the physical nature and to promote the high-field applications. Consequently, in recent years, a stepwise progress has been made in the synthesis of coated conductors (CCs) based on IBS materials, in order to verify their application potential in a high-field regime. We focus this review on the developments and progress in IBS CCs, in particular on application-oriented properties, such as buffer layer, texture, GBs, and transport properties. Here, we provide an overview of the state-of-the-art in three representative IBS systems (11, 122 and 1111 system) widely studied in CCs, along with a detailed description of the fabrication conditions for each system by molecular beam epitaxy or pulsed laser deposition. A summary and comparison of the relations between the superconducting layers and metal tape templates will be presented. An overview and upcoming research and development outlook for IBS CCs is presented in the conclusion.

Atomic Imaging and Thermally Induced Dynamic Structural Evolution of Two-Dimensional Cr2S3.

In this study, facile salt-assisted chemical vapor deposition (CVD) was used to synthesize ultrathin non-van der Waals chromium sulfide (Cr2S3) with a thickness of ∼1.9 nm. The structural transformation of as-grown Cr2S3 was studied using advanced in situ heating techniques combined with transmission electron microscopy (TEM). Two-dimensional (2D) and quasi-one-dimensional (1D) samples were fabricated to investigate the connection between specific planes and the dynamic behavior of the structural variation. The rearrangement of atoms during the phase transition was driven by the loss of sulfur atoms at elevated temperatures, resulting in increased free energy. A decrease in the ratio of the (001) plane led to an overall increase in surface energy, thus lowering the critical phase transition temperature. Our study provides detailed insight into the mechanism of structural transformation and the critical factors governing transition temperature, thus paving the way for future studies on intriguing Cr-S compounds.

Increased exchange interaction range by Fe substitution in Ni3-xFexAl: Evidence from critical behavior

The critical behavior of Fe substituted intermetallic compounds Ni3-xFexAl (x = 0, 0.18, and 0.36) has been investigated around the paramagnetic-ferromagnetic (PM-FM) phase transition based on the static magnetization data. Reliable critical exponents (β, γ, and δ) and transition temperature TC are determined for the compounds, by using Modified Arrott plot, Kouvel-Fisher plot, and critical isotherm plot. The self-consistence and reliability of the obtained critical exponents are further verified by the Widom scaling relation δ = 1 + γ/β and scaling equations of the state M(H,ε) = εβf±(H/εβ+γ). It is found that, Fe substitution for Ni dramatically increases TC from 44.44 K for x = 0 to 301.20 K for x = 0.36. The critical exponents for the three compounds are all found to follow mean-field model. The exchange interaction J(r) is found to decay asr-4.657,r-4.434, and r-4.257 for x=0, 0.18 and 0.36, respectively. The results suggest that, a long range mean-field spin interaction dominates in Ni3-xFexAl (0≤x≤0.36) series. Furthermore, Fe substitution to Ni site is found to increase the spin interaction distance to longer range.

Effects of different temperatures and loads on the tribological behavior of foamed iron-reinforced SiCp/A359 composites

Purpose To improve the high-temperature wear properties of the SiCp/A359 composite, foamed iron-reinforced SiCp/A359 composite (A359–SiCp/Fe) is prepared. The purpose of this study is to investigate the tribological behavior and mechanism of the A359–SiCp/Fe composites at different temperatures (100–500 °C) and loads (7 N, 10 N and 12 N). Design/methodology/approach The A359–SiCp/Fe composite was fabricated by vacuum-assisted infiltration. The dry sliding tribological behaviors of A359–SiCp/Fe composite were investigated using the ball-on-disc-type tribometer. The worn surface and wear morphology of the longitudinal section were examined using field emission scanning electron microscopy and metallographic microscope. Findings The critical transition temperature for severe wear in A359–SiCp/Fe composite was 50–100 °C higher than in SiCp/A359 composite. Foamed iron prevents exfoliation cracks from penetrating deeper into the matrix. The friction coefficient stability of the A359–SiCp/Fe composite was higher than the unreinforced composite at elevated temperatures. With the increase in temperature, the friction-affected layer was severely worn, and the wear mechanism transferred from abrasion and delamination to oxidation and plastic flow, respectively. Originality/value The preparation procedure for aluminum matrix composites reinforced with foamed metal has been less reported, and the research on the tribological behavior and mechanism of A359–SiCp/Fe composite at various temperatures is insufficient. The foamed iron structure considerably enhances the wear properties of SiCp/A359 composite in elevated temperature conditions.

Synthesis, Characterizations, and Thermochromic Properties of VO2 Particles Grafted with PSS : PEDOT

Vanadium dioxide (VO2) particles were modified by grafting with poly(styrene sulfonate) (PSS) and poly(3,4-ethylenedioxythiophene) (PEDOT) via surface-initiated atom transfer radical polymerization (SI-ATRP). Critical transition temperature ( T c ) of the modified VO2 ranging between 77 and 79°C was obtained. After mixing with acrylic-based emulsion, dispersion of the VO2 particles in the polymer matrix was significantly improved. The visible light transmittance through the composite films above 75% was maintained if a concentration of the modified VO2 particles loaded into acrylic polymer film was no greater than 1.0 wt%. The NIR transmittance through the acrylic/VO2@PSS : PEDOT also dropped by 9-10%, compared with that of the pure acrylic film (without any particles). Finally, glass substrates coated with the acrylic/VO2@PSS : PEDOT composite films could reduce the temperature inside a model house by 5-6°C, compared with that of the control system (pure acrylic coating film without VO2 particles). Overall, this work demonstrated that it was possible to improve the dispersion of VO2 particles in polymer films without sacrificing its NIR shielding ability by grafting the surface of VO2 particles with PSS : PEDOT chains, while providing the optimum grafting density and particle loading.

A Thermal-Switchable Metamaterial Absorber Based on the Phase-Change Material of Vanadium Dioxide.

This article presents a thermal-switchable metamaterial absorber (TSMA) based on the phase-change material of vanadium dioxide (VO2). VO2 thin film was deposited on sapphire substrate by magnetron sputtering followed by vacuum annealing treatment. Then, the prepared VO2 film was sliced into tiny chips for thermal-switchable elements. The surface structure of TSMA was realized by loading four VO2 chips into a square metallic loop. The absorption frequency of TSMA was located at 7.3 GHz at room temperature and switched to 6.8 GHz when the temperature was heated above the critical phase transition temperature of VO2. A VO2-based TSMA prototype was fabricated and measured to verify this design. The design is expected to be used in metasurface antennas, sensors, detectors, etc.

The Successful Incorporation of Nd Into Ba Site of Y0.9Ho0.1Ba2-yNdyCu3O7-δ Bulk Superconductors

Abstract: This inclusive study reports the effect of the Nd atoms on the mechanical, microstructural, electrical and superconducting characteristics of Y0.9Ho0.1Ba2-yNdyCu3O7-δ superconductors with the aid of standard characterization methods, including X-ray diffraction, scanning electron microscopy, the bulk density, dc resistivity, and transport critical current density. The experimental results such as the degree of granularity, hole localization effect, room temperature resistivity, critical transition temperature, degree of the broadening, thermodynamic fluctuations, crystallinity, crystal plane alignments, crystal structure, grain size, phase purity and lattice parameters, the appearance of flux pinning centers, grain boundary weak-links, surface morphologies elemental compositions and distributions belonging to Y-site Ho and Ba-site Nd substituted Y-123 superconducting samples are discussed in detail for the first time. All the experimental findings show that the microstructural, electrical, mechanical and superconducting properties regularly improve with the increment in the HcN (Ho constant+Nd changeble) until a certain value of y=0.100, beyond which the characteristics tend to retrograde rapidly. This is attributed to the fact that excess penetration of the Nd damages the crucial properties given above.