Nb3Sn Superconductors Research Articles

Unveiling the nucleation and growth of Zr oxide precipitates in internally oxidized Nb3Sn superconductors

We report on atomic-scale analyses of nucleation and growth of Zr oxide precipitates and the microstructural evolution of internally oxidized Nb3Sn wires for high-field superconducting magnet applications, utilizing atom probe tomography (APT), transmission electron microscopy (TEM), and first-principles calculations. APT analyses reveal that oxygen and zirconium are already segregated at grain boundaries (GBs) in the unreacted Nb-1Zr-4Ta (at%) alloy prior to forming Nb3Sn through reacting the Nb alloy with Sn and SnO2. After forming Nb3Sn, Zr oxide precipitates nucleate both at the Nb3Sn/Nb heterophase interfaces and in the Nb3Sn grains, driven by the small solubilities of Zr and O in Nb3Sn compared to their value in Nb. A high number density (Nv) of Zr oxide nanoprecipitates is observed in the Nb3Sn layers, ∼1023 m−3, with a mean diameter <10 nm for a heat treatment at 625 °C. Quantitative APT and TEM analyses of the Zr oxide precipitates in the reacted Nb3Sn layers elucidate details of the nucleation, growth, and coarsening processes of the Zr oxide precipitates in Nb3Sn. First-principles calculations and classical nucleation theory are employed to study the nucleation of Zr oxide precipitates in Nb3Sn and to estimate the maximum energy barrier and critical radius for nucleation. Our research unveils the kinetic pathways for nucleation and growth of Zr oxide precipitates and the microstructural evolution of Nb3Sn layers, which helps to understand and improve the superconducting properties of internally oxidized Nb3Sn wires for use in high-field superconducting magnets.

Extensive Search for Axion Dark Matter over 1 GHz with CAPP’S Main Axion Experiment

We report an extensive high-sensitivity search for axion dark matter above 1 GHz at the Center for Axion and Precision Physics Research (CAPP). The cavity resonant search, exploiting the coupling between axions and photons, explored the frequency (mass) range of 1.025 GHz (4.24 μeV) to 1.185 GHz (4.91 μeV). We have introduced a number of innovations in this field, demonstrating the practical approach of optimizing all the relevant parameters of axion haloscopes, extending presently available technology. The CAPP 12 T magnet with an aperture of 320 mm made of Nb3Sn and NbTi superconductors surrounding a 37 l ultralight-weight copper cavity is expected to convert Dine-Fischler-Srednicki-Zhitnitsky axions into approximately 102 microwave photons per second. A powerful dilution refrigerator, capable of keeping the core system below 40 mK, combined with quantum-noise-limited readout electronics, achieved a total system noise of about 200 mK or below, which corresponds to a background of roughly 4×103 photons per second within the axion bandwidth. The combination of all those improvements provides unprecedented search performance, imposing the most stringent exclusion limits on axion-photon coupling in this frequency range to date. These results also suggest an experimental capability suitable for highly sensitive searches for axion dark matter above 1 GHz. Published by the American Physical Society 2024

Nuclear magnetic resonance investigation of superconducting and normal state Nb3Sn

The superconductor Nb3Sn has important applications for construction of very high-field superconducting magnets. In this work we investigate its microscopic electronic structure with 93Nb nuclear magnetic resonance (NMR). The high-quality Nb3Sn powder sample was studied in both 3.2 T and 7 T magnetic fields in the temperature range from 4 K to 300 K. From measurement of the spectrum and its theoretical analysis, we find evidence for anisotropy despite its cubic crystal structure. Magnetic alignment of the powder grains in the superconducting state was also observed. The Knight shift and spin-lattice relaxation rate, T1−1 , were measured and the latter compared with BCS theory for the energy gap Δ(0)=2.7±0.3kBTc at 3.2 T and Δ(0)=2.33±0.07kBTc at 7 T, indicating suppression of the order parameter by magnetic field.

Исследование влияния термической обработки на структуру и механические свойства полуфабрикатов из сплава NbTa(Zr,Hf,Y), предназначенных для изготовления Nb3Sn сверхпроводников

The influence of the degree of deformation and annealing on the mechanical properties of Nb-based alloy samples of different compositions: Nb-Ta-Zr, Nb-Ta-Hf, Nb-Ta-Zr-Y used in the manufacture of Nb3Sn superconductors is studied. The deformability of Nb-based alloys in the composition of single-fiber composite Nb3Sn superconductors, which were manufactured using the technology of an internal tin source and the «powder – in – tube» method, has been studied. It is shown that the values of the time resistance of samples with a sheath made of Nb alloys 7.5 wt.% Ta–0.5 wt.% Zr and Nb–7.5 wt.% Ta–1 wt. % Zr are at the same level of ~ 650 MPa, and the elongation values are ~ 2%. The structural features of the fracture surface of Nb-based alloy samples with varying degrees of accumulated deformation and single-fiber conductors have been studied. The results of the work will be used in the development of technological modes for manufacturing Nb3Sn-based superconductors.

Influence of a high magnetic field to the design of EU DEMO

The limitation considered in the definition of DEMO in 2016 to not exceed the magnetic field strength foreseen in the ITER machine is reviewed here. At the time, a Nb3Sn superconductor operated in a magnetic field, Bmax, no greater than 13 T was considered to rely on existing and mature technology. This limitation is no longer seen as a boundary here, recognizing that the first model coil with Rare Earth Yttrium Barium Copper Oxid (REBCO) superconductor was recently operated at a field of >20 T.DEMO must have a burning plasma which, at a higher magnetic field, is reached in a significantly smaller plasma volume. Accordingly, a system code study was carried out to size the DEMO machine by varying the magnetic field. The outcome confirmed previous observations that the magnetic field strength is linearly dependent on the plasma aspect ratio, A, when we target a minimum machine size. It was notable that in a machine with a high A, the increased Bmax raises the plasma performance but does not allow for reducing its size. The reduced plasma elongation of plasmas with high aspect ratio is a caveat as it reduces the gain in plasma performance achieved in the high field. Furthermore, the higher magnetic field at high A challenges the engineering of the magnets and associated structures, and substantially increases the heat loads on the divertor. This article assesses the engineering feasibility assessment of large DEMO coils operated at high field, also considering advanced i.e., non-ITER like, mechanical concepts. No advanced coil concepts appeared suitable for a large device like DEMO. Consequently, DEMO design points with lower Bmax and lower A were investigated. This resulted in the identification of a maximum magnetic field of approximately 11–12 T to ensure the engineering feasibility of the DEMO TF coils.

Conceptual Design of 20 T Hybrid Accelerator Dipole Magnets

Hybrid magnets are currently under consideration as an economically viable option towards 20 T dipole magnets for next generation of particle accelerators. In these magnets, High Temperature Superconducting (HTS) materials are used in the high field part of the coil with so-called insert coils, and Low Temperature Superconductors (LTS) like Nb3Sn and Nb-Ti superconductors are used in the lower field region with so-called outsert coils. The attractiveness of the hybrid option lays on the fact that, on the one hand, the 20 T field level is beyond the Nb3Sn practical limits of 15-16 T for accelerator magnets and can be achieved only via HTS materials; on the other hand, the high cost of HTS superconductors compared to LTS superconductors makes it advantageous exploring a hybrid approach, where the HTS portion of the coil is minimized. We present in this paper an overview of different design options aimed at generating 20 T field in a 50 mm clear aperture. The coil layouts investigated include the Cos-theta design (CT), with its variations to reduce the conductor peak stress, namely the Canted Cos-theta design (CCT) and the Stress Management Cos-theta design (SMCT), and, in addition, the Block-type design (BL) including a form of stress management and the Common-Coil design (CC). Results from a magnetic and mechanical analysis are discussed, with particular focus on the comparison between the different options regarding quantity of superconducting material, field quality, conductor peak stress, and quench protection.

The effect of antisite defects on the mechanical and dynamic stability of Nb3Al

The A15-type conventional superconductor Nb3Al alloys has been considered as an ideal candidate for next generation high field magnets due to its higher superconducting properties and less sensitivity to stain than that of industrialized Nb3Sn superconductor. First-principles methods are employed to study the potential point defects, vacancy and antisite defects in deviating stoichiometric Nb3Al alloys and their effect on structure and mechanical properties. Our results show that antisite defects are easier to be produced than vacancy defects, and Nb antisite defects can keep the tetragonal structure of Nb3Al. Furthermore, the influence of antisite defects on dynamic stability of Nb3Al is investigated together with Nb defects. With the increase of Nb antisite defect content and the formation of orderly arrangement, we found the phonon spectrum yields no more soft phonon modes, which is in contradiction with the dynamical instability of stoichiometric Nb3Al with no defects. Our calculations indicate Nb antisite defects play a crucial role on the dynamic stability of Nb3Al compounds.

Characteristic Length for Pinning Force Density in Nb3Sn.

The pinning force density, Fp, is one of the main parameters that characterize the resilience of a superconductor to carrying a dissipative-free transport current in an applied magnetic field. Kramer (1973) and Dew-Hughes (1974) proposed a widely used scaling law for this quantity, where one of the parameters is the pinning force density maximum, Fp,max, which represents the maximal performance of a given superconductor in an applied magnetic field at a given temperature. Since the late 1970s to the present, several research groups have reported experimental data on the dependence of Fp,max on the average grain size, d, in Nb3Sn-based conductors. Fp,maxd datasets were analyzed and a scaling law for the dependence Fp,maxd=A×ln1/d+B was proposed. Despite the fact that this scaling law is widely accepted, it has several problems; for instance, according to this law, at T=4.2 K and d≥650 nm, Nb3Sn should lose its superconductivity, which is in striking contrast to experiments. Here, we reanalyzed the full inventory of publicly available Fp,maxd data for Nb3Sn conductors and found that the dependence can be described by the exponential law, in which the characteristic length, δ, varies within a remarkably narrow range of δ=175±13 nm for samples fabricated using different technologies. The interpretation of this result is based on the idea that the in-field supercurrent flows within a thin surface layer (thickness of δ) near grain boundary surfaces (similar to London's law, where the self-field supercurrent flows within a thin surface layer with a thickness of the London penetration depth, λ, and the surface is a superconductor-vacuum surface). An alternative interpretation is that δ represents the characteristic length of the exponential decay flux pinning potential from the dominant defects in Nb3Sn superconductors, which are grain boundaries.

Thermodynamic route of Nb3Sn nucleation: Role of oxygen

Intermetallic Nb3Sn alloys have long been believed to form through Sn diffusion into Nb. However, our observations of significant oxygen content in Nb3Sn prompted an investigation of alternative formation mechanisms. Through experiments involving different oxide interfaces (clean HF-treated, native oxidized, and anodized), we demonstrate a thermodynamic route that fundamentally challenges the conventional Sn diffusion mechanism for Nb3Sn nucleation. Our results highlight the critical involvement of a SnOx intermediate phase. This new nucleation mechanism identifies the principles for growth optimization and new synthesis of high-quality Nb3Sn superconductors.

Significant reduction in the low-field magnetization of Nb3Sn superconducting strands using the internal oxidation APC approach

Nb3Sn superconductors are promising for building accelerator magnets for future energy-frontier circular colliders. A critical factor for this application is the low-field persistent-current magnetization because it leads to several critical issues: e.g. low-field instability (including flux jumps), hysteresis loss, and field errors in magnet bores. Suppression of low-field magnetization requires reduction of low-field critical current density (J c) or effective subelement size (d eff). However, reduction of d eff of state-of-the-art Nb3Sn conductors—the restacked-rod-process (RRP®) type—below 40–50 μm without a pronounced decrease in high-field J c is difficult. On the other hand, the internal oxidation method which forms artificial pinning centers (APC) in Nb3Sn offers an alternative approach to reducing the low-field magnetization. Compared with a conventional Nb3Sn conductor whose flux pinning force versus field (F p–B) curve peaks at ∼20% of its irreversibility field (B irr), the F p–B curve peaks of APC conductors shift to higher fields due to the point pinning effect, leading to flattening of the J c–B curves. The goal of this paper is to quantitatively study how much the APC approach can reduce the low-field magnetization. We measured the J c–B curves of an RRP® conductor and two APC conductors (reacted at 700 °C) from zero field to B irr using a high-field vibrating sample magnetometer. The results showed that the APC conductors have higher non-Cu J c at high fields (e.g. 32%–41% higher at 16 T) and simultaneously lower non-Cu J c at low fields (e.g. 28%–34% lower at 1 T) compared with the RRP®. This effect is due to a competition between their Nb3Sn layer fraction ratios and layer F p ratios. Suppose they reach the same 16 T non-Cu J c, then the 1 T non-Cu J c and magnetization of the APC conductors are only half or even less compared with the RRP® conductor.

Development of superconducting model dipole magnets beyond 12 T with a combined common-coil configuration

The superconducting magnet group at IHEP (the Institute of High Energy Physics, Chinese Academy of Sciences, China) has been engaging in the R&D of high field accelerator magnets since 2014 for the pre-study of the next-generation high energy particle accelerators like CEPC-SPPC (Circular Electron Positron Collider-Super Proton Proton Collider), FCC (Future Circular Collider), etc. A superconducting model dipole magnet named LPF1 was first fabricated with NbTi and Nb3Sn in a combined common-coil configuration in 2017 and tested in 2018, a main field of 10.23 T was reached within two 10 mm apertures. The magnet was reassembled with higher pre-stress in 2019 to investigate the influence of the pre-stress loading level on the performance of common-coil dipole magnets. The main field of this upgraded magnet named LPF1-S was increased to 10.71 T within two 12 mm apertures. By improving the key processing technologies in Rutherford cable fabrication, coil winding, Nb3Sn & NbTi splices soldering and coil impregnation, the recently fabricated model dipole magnet named LPF1-U attained a 12.47 T main field in two 14 mm apertures in 2021. To fully take advantage of Nb3Sn and NbTi superconductors in different field regions, LPF1-U was still designed and developed with a combined coil configuration with Nb3Sn for the inner two coils and NbTi for the outer four coils. Additionally, graded coil topology and different coil LSS (length of straight section) settings were adopted in the optimization of LPF1-U layouts. Bladder and key technology was used for the support structure, and fiber optic sensors based on FBG (fiber Bragg grating) were utilized to monitor the stress distribution and variation in the structures and coils through the whole process from magnet assembly to cool-down and excitation. During the performance test, a relatively large number of trainings were carried out and LPF1-U became more stable after the thermal cycle. A peak field of 12.7 T in the coils (12.47 T main field in apertures) corresponds to an operating current of 6865 A and a load line ratio of 90% was finally attained. It is worth mentioning that LPF1-U is the first hybrid—Nb3Sn, NbTi—common coil dipole magnet that has achieved a main field of more than 12 T in two apertures. The design, fabrication and performance analysis of the LPF series dipole magnets are presented in this paper.

Phase Transition of Nb3Sn during the Heat Treatment of Precursors after Mechanical Alloying

The phase transition process of Nb3Sn during heat treatment exerts important influences on Nb3Sn formation and the superconducting characteristics of Nb3Sn superconductors. A simple method for quickly preparing Nb3Sn was studied. First, Nb, Sn, and Cu powders were mechanically alloyed to prepare the precursor. Then, the precursor was heat treated at different times to form Nb3Sn. During the first stage, the morphology and crystal structure of the products were analyzed after different milling times. The results of the transmission electron microscopy showed the poor crystallinity of the products compared with the original materials. During the second stage, heat treatment was performed at different temperatures ranging from room temperature to 1073 K. After treatment, the products were studied via X-ray diffraction analysis to determine how the structure changed with increasing temperature. Only the Nb diffraction peaks in the precursor were observed after high-energy ball milling for more than 3 h. When the heat treatment temperature was above 773 K and heat treatment time was 15 min, Nb3Sn began to form. When the temperature was above 973 K, some impurities, such as Nb2O5, appeared. After 5 h of ball milling, the precursor was heat treated at different times in a vacuum heat treatment furnace. The crystal structure of the product exhibited evident diffraction peaks of Nb3Sn. The critical temperatures of the samples that were heat treated at different times were between 17 K and 18 K. The magnetic critical current density of the sample versus the applied magnetic field at 4.2 K indicated that the magnetic Jc was approximately 30,000 A/cm2.

Effect of independent alloying of zirconium with bronze and niobium on superconducting properties of Nb3Sn in a Cu(Sn)/Nb system

The present work focuses on the effect of internal (niobium) and external (bronze) alloying of Zr on the superconducting properties of Nb3Sn in a Cu(Sn)/Nb system through the diffusion couple method. Alloying of Zr with either Cu(5.5 at.% Sn) or Nb enhances the critical current density (Jc) of the Nb3Sn superconductor phase developed at the interdiffusion zone of Cu(5.5 at.% Sn, 2 at.% Zr)/Nb and Cu(5.5 at.% Sn)/Nb(2 at.% Zr). Enhancement of Jc of Zr-alloyed Nb3Sn has been attributed to an increment in grain boundary fraction for Nb3Sn. Dew Hughes model provided an insight into the pinning mechanisms responsible for enhancement of Jc. Strengthening of pinning forces of Nb3Sn with internal alloying of Zr might have originated because of the nanometer-sized β-(Nb, Zr) second-phase developed within the Nb3Sn phase matrix. No change in critical temperature for Zr-alloyed Nb3Sn makes Zr a suitable alloying element for applications.

Critical current density enhancement of Nb3Sn superconducting wires by incorporating oxygen through rapid-heating method

The critical current density (Jc) still has much room for improvement for Nb3Sn superconductors. In this paper, SnO2 is doped into powder-in-tube (PIT) Nb3Sn superconducting wires as the oxygen source through rapid heating, quenching and annealing (RHQA) process. The results show that the 1.5 wt% SnO2-doped Nb3Sn has much higher Jc@4.2 K,10 T than the pure sample after RHQ at 2150 °C in 2 s. This is not the case when the Nb3Sn wires RHQ at 1700 °C. The increase in Jc is related to a decrease in grain size and an enhancement of inter-grain connectivity.

APC Nb3Sn superconductors based on internal oxidation of Nb–Ta–Hf alloys

In the last few years, a new type of Nb3Sn superconducting composite, containing a high density of artificial pinning centers (APC) generated via an internal oxidation approach, has demonstrated a significantly superior performance relative to present, state-of-the-art commercial Nb3Sn conductors. This was achieved via the internal oxidation of Nb-4at.%Ta-1at.%Zr alloy. On the other hand, our recent studies have shown that internal oxidation of Nb–Ta–Hf alloys can also lead to dramatic improvements in Nb3Sn performance. In this work we follow up on this latter approach, fabricating a 61-stack APC wire based on the internal oxidation of Nb-4at.%Ta-1at.%Hf alloy, and compare its critical current density (J c) and irreversibility field with APC wires made using Nb-4at.%Ta-1at.%Zr. A second goal of this work was to improve the filamentary design of APC wires in order to improve their wire quality and electromagnetic stability. Our new modifications have led to significantly improved residual resistivity ratio and stability in the conductors, while still keeping non-Cu J c at or above the conductor J c specification required by the proposed Future Circular Collider. Further improvement via optimization of the wire recipe and design is ongoing. Finally, additional work needed to make APC conductors ready for applications in magnets is discussed.

The role of copper in the formation of the Nb3Sn superconducting phase

Nb3Sn has been widely used in high magnetic field facilities due to its excellent superconducting properties. Moreover, copper has become an indispensable constituent element in the fabrication of Nb3Sn superconductors. However, the role of copper in the formation of the Nb3Sn phase is still not thoroughly understood. In this work, Nb–Sn–Cu ternary samples with different molar ratios of copper were prepared by sintering elemental Nb, Sn and Cu mixed powders, and the effect of copper on the formation of the Nb3Sn phase was systematically investigated. It was found that the addition of copper had a significant effect on the formation of Nb3Sn. When the amount of added copper was small, the formation of the Nb3Sn phase was efficiently promoted with the aid of the liquid phase, and a high-purity sample of Nb3Sn could be formed by the transition from the Nb–Sn binary phases. However, at the same time, the bulk samples with a low ratio of copper possessed poor compactness due to the pressure build-up and tin burst generated by the liquid phase during heat treatment. With increasing copper content, the promotion effect became relatively weaker. More high melting temperature Cu–Sn phases were formed, and Nb3Sn was gradually formed by solid-state diffusion between Nb and the Cu–Sn matrix. Finally, it was found that the sample of Nb:Sn:Cu = 3:1:3 (mol. %) with a grain size of 70–120 nm possessed the highest critical current density due to its high phase purity and fine grain size of Nb3Sn.

Improving critical current density of Nb3Sn by optimizing pinning potential of grain boundary and grain size

Nb3Sn superconductor is of significant interest for applications in constructing high-field magnets beyond the limit of NbTi. However, its critical current density decreases rapidly at high magnetic fields (12 T) and the state-of-the-art level of Nb3Sn superconductors still cannot meet the requirements of the planned future accelerator magnets. The primary flux pinning centers for Nb3Sn wire mainly arise from the grain boundaries (GBs). In the present paper, we theoretically investigate, through time-dependent Ginzburg-Landau theory and with graphics-processing unit parallel technique, the vortex pinning and the critical current density in large-scale polycrystalline Nb3Sn superconductor by varying the pinning potential of GB and grain size at various magnetic fields. Unlike the conventional dot-like pinning systems, it is found that the critical current is not a monotonous function by suppressing the superconductivity of the GBs. The optimal pinning potential of GB for maximum critical current density strongly depends on magnetic fields. Furthermore, we find that the critical current density can be significantly enhanced by reducing grain size at low magnetic fields, while increase of critical current density cannot always be observed at high magnetic fields. Actually, critical current density even decreases by reducing grain size, which depends on the superconductivity of GBs. The findings in the paper provide theoretical foundations to achieve further improvement of Nb3Sn with optimizing the flux pinning.

Impact of Ti-doping position on Nb3Sn layer formation in internal Sn-processed Nb3Sn superconducting wires

Further enhancement of critical current density of Nb3Sn superconductors is still of great interest and challenging towards realization of leading-edge magnets such as the future circular collider (FCC) and demonstration Power Station (DEMO) fusion reactors. In this study, the influence of the Ti-doping position on the Nb3Sn layer formation in internal Sn-processed Nb3Sn superconducting wires, which has not been sufficiently clarified yet, was investigated using the simplest diffusion pair structure that consists of a single Nb/Cu/Sn layer. Three types of specimens were prepared, in which Ti was doped into the Sn core, Nb, and Cu matrix (denoted as ST, NT, and CT, respectively). The NbCuSnTi compound phase appeared as a diffusion barrier at the boundary between the Nb3Sn and Cu–Sn phases in the ST and CT samples and remained during the Nb3Sn layer formation, although it was absent in NT. The electron backscatter diffraction analysis of the formed Nb3Sn grain morphologies showed no significant difference in terms of the average grain size and area fraction of the equiaxed grains regardless of the doping position. However, the average Nb3Sn layer thickness of NT was at least 1.6 times larger than that of ST and CT. The absence of the NbCuSnTi phase promotes Sn diffusion into Nb, which accounts for the thicker Nb3Sn layer and much higher Ic–B characteristics in NT.

The Manufacture and Performance of Low Temperature Superconductors

The application of Nb3Sn superconductor joints is an important part in the production of ITER, MRI and so on. This paper first introduced the application, like coil of MRI, and basic information including the micro crystal structure of Nb3Sn superconductor, which includes the theoretical critical temperature of 18.1K, even mostly, experiments take place under 4.2K, which is the boiling point of liquid helium. Second, it talked a little about the production of CICC joints in industry. Then, mainly introduced the testing device, material parameters and testing procedures of resistance testing of Nb3Sn joints. Concluded all the data from several tests and summarized it. At last, it displayed some of its mechanical property especially about its brittle property and discussed some details in manufacture. Finally conclude about them all.

Nb/Sn Liquid-Solid Reactive Diffusion Couples and Their Application to Determination of Phase Equilibria and Interdiffusion Coefficients of Nb-Sn Binary System.

Nb3Sn plays an irreplaceable role in superconducting parts due to its stable performance under high field conditions. Accurate phase equilibria and interdiffusion coefficients are of great significance for designing novel Nb3Sn superconductors. However, the related experimental information is still in a state of scarcity because of the difficulty in fabrication of Nb-Sn alloys caused by the large difference in melting points of Nb and Sn. In this paper, a simple but pragmatic approach was first proposed to prepare the Nb/Sn liquid-solid reactive diffusion couples (LSDCs) at 1100 °C and 1200 °C, of which the phase identification of the formed layer and the measurement of composition-distance profiles were conducted. The formed layer in Nb/Sn LSDCs was confirmed to be Nb3Sn compound. While the measured composition profiles were employed to determine the phase equilibria according to the local equilibrium hypothesis and the interdiffusion coefficients with an aid of the latest version of HitDIC software. The determined phase equilibria of Nb3Sn, (Nb) and liquid show good agreement with the assessed phase diagram. While the calculated interdiffusion coefficients and activation energy for diffusion in Nb3Sn are consistent with both experimental and theoretical data in the literature. Moreover, the growth of the formed Nb3Sn layer in Nb/Sn LSDCs was also found to be diffusion controlled. All the obtained phase equilibria and interdiffusion coefficients are of great value for further thermodynamic and kinetic modeling of the Nb-Sn system. Furthermore, it is anticipated that the presently proposed approach of fabricating liquid-solid reactive diffusion couple should serve as a general one for various alloy systems with large differences in melting points.