Sn Flux Research Articles

Promoting subsurface Sn incorporation at Nb(100) oxide surface sites leading to homogeneous Nb3Sn film growth for superconducting radiofrequency applications

For next-generation superconducting radiofrequency (SRF) cavities, the interior walls of existing Nb SRF cavities are coated with a thin Nb3Sn film to improve the superconducting properties for more efficient, powerful accelerators. The superconducting properties of these Nb3Sn coatings are limited due to inhomogeneous growth resulting from poor nucleation during the Sn vapor diffusion procedure. To develop a predictive growth model for Nb3Sn grown via Sn vapor diffusion, we aim to understand the interplay between the underlying Nb oxide morphology, Sn coverage, and Nb substrate heating conditions on Sn wettability, intermediate surface phases, and eventual Nb3Sn nucleation. In this work, Nb-Sn intermetallic species are grown on a single crystal Nb(100) in an ultrahigh vacuum chamber equipped with in situ surface characterization techniques including scanning tunneling microscopy, Auger electron spectroscopy, and x-ray photoelectron spectroscopy. Sn adsorbate behavior on oxidized Nb was examined by depositing Sn with submonolayer precision on a Nb substrate held at varying deposition temperatures (Tdep). Experimental data of annealed intermetallic adlayers provide evidence of how Nb substrate oxidization and Tdep impact Nb-Sn intermetallic coordination. The presented experimental data contextualize how vapor and substrate conditions, such as the Sn flux and Nb surface oxidation, drive homogeneous Nb3Sn film growth during the Sn vapor diffusion procedure on Nb SRF cavity surfaces. This work, as well as concurrent growth studies of Nb3Sn formation that focus on the initial Sn nucleation events on Nb surfaces, will contribute to the future experimental realization of optimal, homogeneous Nb3Sn SRF films.

Effect of βSn grain orientations on the electromigration-induced evolution of voids in SAC305 BGA solder joints

The electromigration (EM) failure of solder joints is closely related to the development of voids during EM. In this paper, an integrated approach combining experimentation and finite element simulation was employed to reveal the evolution of voids in solder joints under current stress. The results indicate that the quantity and volume of voids near the cathode consistently increase, while those close to the anode decrease. These asymmetric evolutions of voids are mainly due to the Sn flux, which is controlled by both current density and βSn grain orientation. The magnitude of Sn flux increases with higher current densities and larger angles γ between the c-axis of βSn and the current direction. The direction of Sn flux is more significantly influenced by the current direction rather than the βSn orientation, due to the weak anisotropic self-diffusion of Sn. Voids near the anode tend to shrink while those close to the cathode expand, parallel to the substrate, due to higher Sn flux distributions at the waists of voids, where current crowding is seen. Void splitting related to rapid Cu diffusion has been observed, leading to an abnormal increase in the number of voids near the cathode. This study enhances the understanding of the electromigration failure mechanisms involving void evolution in solder joints.

The La2Pd3(Si, Ge)5 complete solid solution: Crystal structure, chemical bonding, and volume chemistry

The La2Pd3Si5 intermetallic and the La2Pd3(SixGe1-x)5 solid solution were targeted for structural and computational investigations. The ternary compound and quaternary alloys with varying silicon contents (x = 0.25, 0.50, 0.70, 0.75) were prepared by arc melting and turned out to crystalize with the oI40–U2Co3Si5 (Ibam, N. 72) type structure based on powder X-ray diffraction data. The crystal structure of La2Pd3Si5 was additionally solved through X-ray diffraction on single crystal grown by recrystallization in Sn flux. Chemical bonding investigations based on QTAIM effective charges and DOS/(I)COHP analysis indicate the formation of heteropolar interactions between Si and the surrounding La/Pd metals, and between La and Pd. Covalently bonded zigzag chains of Si are also formed and considered to be the main responsible for the higher melting point of La2Pd3Si5, measured by DSC, with respect to that of La2Pd3Ge5. The formation of a complete solid solution between La2Pd3Si5 and La2Pd3Ge5 was confirmed and refined unit cell parameters and volumes change linearly with composition, displaying a Vegard trend. The calculation of atomic volumes on a quantum chemical basis (QTAIM) provides detailed insights into the volume chemistry of La2Pd3(SixGe1-x)5. Through this analysis La is found to be responsible, together with the gradual substitution of Ge with Si, for the volume contraction.

Ironing out the transition metal contribution to the magnetism of the n = 3 members of the homologous series Prn+1MnGe3n+1 (M = Fe, Co): Pr4Fe3Ge10 vs. Pr4Co3Ge10

The Lnn+1MnX3n+1 (Ln = lanthanide, M = transition metal, and X = tetrel) homologous series provides a platform to study collective phenomena in quantum materials. In this work, we compare the crystal growth, structure, and magnetic properties of the n = 3 members of the Prn+1MnGe3n+1 (M = Fe, Co) analogues, Pr4Fe3Ge10 (a = 4.3207 (10) Å, b = 35.523 (8) Å, c = 4.2982 (15) Å, and V = 659.7 (3) Å3) and Pr4Co3Ge10 (a = 4.3091 (12) Å, b = 35.750 (9) Å, c = 4.2807 (11) Å, and V = 659.4 (3) Å3). We determined that the ideal flux growth conditions for each compound are highly dependent on the concentration of Sn flux and quench temperature. Pr4Fe3Ge10 orders ferromagnetically at 10 K along the c-direction while Pr4Co3Ge10 orders antiferromagnetically at 16 K along the b-direction. For both compounds, we observed a magnetic moment higher than that expected for only Pr3+ ions (3.58 µB/Pr), implying that the transition metal ions contribute to magnetic ordering (3.91, 3.48, and 3.69 µB/Pr for Pr4Fe3Ge10, and 3.76, 4.04, and 3.83 µB/Pr for Pr4Co3Ge10 measured along the a-, b-, and c-directions, respectively). Moreover, the zero-field Mössbauer spectrum obtained at 4.2 K for Pr4Fe3Ge10 demonstrates that the iron sites participate in magnetic ordering.

Large positive magnetoresistance and high mobility in topological insulator candidate LaP

We reported herein the single crystal growth and the comprehensive study of basic physical properties including electronic transport, magnetic, specific heat of topological insulator candidate LaP. Single crystal LaP of rock salt type structure was synthesized by Sn flux method. Under low temperature and high magnetic field of T= 2 K and B= 9 T, large positive magnetoresistance (LMR) of 500% was discovered. The Hall effect measurements show that the conduction carriers are dominated by holes among the temperature range from 300 K to 2 K, the carrier concentration n_{h} =4.94times 10^{19} cm−3 and n_{e} =5.02times 10^{16} cm−3 and the mobility of LaP reached as high as mu _{h}=1.57times 10^{4} cm2 V−1 S−1 and mu _{e} = 1.55times 10^{3} cm2 V−1 S−1 obtained at 2 K, which can be explained by multiband model physics like other topological quantum material systems with large MR. LaP shows diamagnetism over a wide temperature range from 2 K to 300 K without any magnetic phase transition by susceptibility measurements. No evidence of phase transitions from 2 K to 300 K was observed in the specific heat measurement. The electronic specific heat coefficient is obtained 0.538 m J mol−1 K−2 for LaP single crystal, which responds to a small electron density state near the Fermi level. Our results would be helpful in renewing interest in studying emergent phenomena arisen from topological semimetals. LaP offers a platform for understanding the interactions between large magnetoresistance, high mobility and topological band structure.

Anisotropic magnetic and transport properties of orthorhombic o-Pr2Co3Ge5

The crystal structure, electron energy-loss spectroscopy (EELS), heat capacity, and anisotropic magnetic and resistivity measurements are reported for Sn flux grown single crystals of orthorhombic Pr2Co3Ge5 (U2Co3Si5-type, Ibam). Our findings show that o-Pr2Co3Ge5 hosts nearly trivalent Pr ions, as evidenced by EELS and fits to temperature dependent magnetic susceptibility measurements. Complex magnetic ordering with a partially spin-polarized state emerges near T sp = 32 K, with a spin reconfiguration transition near T M = 15 K. Heat capacity measurements show that the phase transitions appear as broad peaks in the vicinity of T sp and T M. The magnetic entropy further reveals that crystal electric field splitting lifts the Hund’s rule degeneracy at low temperatures. Taken together, these measurements show that Pr2Co3Ge5 is an environment for complex f state magnetism with potential strongly correlated electron states.

Preparation of large Cu3Sn single crystal by Czochralski method

Cu3Sn was recently predicted to host topological Dirac fermions, but related research is still in its infancy. The growth of large and high-quality Cu3Sn single crystals is, therefore, highly desired to investigate the possible topological properties. In this work, we report the single crystal growth of Cu3Sn by Czochralski (CZ) method. Crystal structure, chemical composition, and transport properties of Cu3Sn single crystals were analyzed to verify the crystal quality. Notably, compared to the mm-sized crystals from a molten Sn flux, the cm-sized crystals obtained by the CZ method are free from contamination from flux materials, paving the way for the follow-up works.

Crystal structure and magnetic properties in semiconducting Eu3−δZnxSnyAs3 with Eu-Eu dimers

Magnetic structure and crystal symmetry, which primarily determine the time-reversal and inversion symmetry, may give rise to numerous exotic quantum phenomena in magnetic semiconductors and semimetals when arranged in different patterns. In this work, a new layered magnetic semiconductor, Eu3−δZnxSnyAs3, was discovered and high-quality single crystals were grown using the Sn flux. According to structural characterization by x-ray diffraction and atomic-resolution scanning transmission electron microscopy, Eu3−δZnxSnyAs3 is found to crystallize in a hexagonal symmetry with the space group P63/mmc (No. 194). After examining different specimens, we conclude that their stoichiometry is fixed at ∼Eu2.6Zn0.65Sn0.85As3, which meets the chemical charge balance. Eu3−δZnxSnyAs3 is composed of septuple (Eu1−δSnyAs2)-Eu-(ZnxAs)-Eu sequences. The shortest Eu–Eu distance in the system is between two Eu layers separated by ZnxAs along the c-axis. Magnetization measurement shows an antiferromagnetic ordering in Eu3−δZnxSnyAs3 at TN ∼ 12 K, where the magnetic easy-axis is along the c-axis, and Mössbauer spectroscopy observes magnetic hyperfine splitting on Eu and Sn at 6 K. Magnetic anisotropy is significantly different from the ones along the ab-plane in other layered Eu-based magnetic semimetals. Heat capacity measurements confirm the magnetic transition around 12 K. Electrical resistivity measurement indicates semiconductor behavior with a band gap of ∼0.86 eV. Various Eu-based magnetic semiconductors could provide a tunable platform to study potential topological and magnetic properties.

Effect of Na–Sn Flux on the Growth of Type I Na8Si46 Clathrate Crystals

In the crystal growth of Na–Si clathrate (type I, Na8Si46) during Na evaporation from a Na–Si–Sn solution at 723 K, the composition of a Na–Sn flux in the starting material strongly influences the morphology and size of the formed clathrate crystals. In this study, the crystals obtained using this flux were larger than the crystals prepared without a flux, and some of them had faceted surfaces. At the Na4Si4 (precursor):4Na–Sn (flux) = 1:4 ratio, multiple dents were observed on crystal surfaces, indicating that the precipitation of a Na9Sn4 solid phase prevented the growth of Na–Si clathrate crystals. In addition, synthesis conditions, under which type I crystals could be obtained by conventional thermal decomposition in vacuum, were established. The results of this work suggest that type I Na–Si clathrate crystals are stable even at temperatures as high as 723 K due to the suppressed evaporation of Na.

Structure, magnetic anisotropy and magnetocaloric effect of Mn5Ge3-xSix single crystals

Magnetocaloric polycrystalline materials based on Mn5Ge3 have been widely studied due to their potential application for room temperature magnetic refrigeration. However, many investigations are performed on polycrystalline materials and thus the strong anisotropy in this layered structure is usually neglected. In this study, Mn5Ge3-xSix (x = 0, 0.7) single crystals were successfully synthesized via Sn flux and characterized by single-crystal X-ray diffraction and magnetic measurements. The Si substitution does not change the structural symmetry, but reduces the shortest Mn − Mn distances. As described by the Bethe-Slater curve, the reduction of the shortest Mn − Mn distances leads to weaker magnetic exchange, accounting for the lower ordering temperature. The magnetocrystalline anisotropy was evaluated by the Sucksmith and Thompson method, and became smaller upon substitution. The anisotropy constants K1 and K2 of Mn5Ge3-xSix (x = 0, 0.7) single crystals are positive, and decrease with the temperature. The electron paramagnetic resonance spectra suggest high spin d5 configuration of manganese in both crystals. The easy magnetization direction yields much larger maximum entropy changes in both crystals: 6.0 J/kg K for the pristine and 5.4 J/kg K for the substituted under an applied field of 30 kOe.

Conserved axis-dependent conduction polarity in NaSnAs polycrystalline bulk sample for transverse thermoelectric application

Layered semiconductor NaSnAs has a distinct property of large anisotropy in effective mass, resulting in axis-dependent conduction polarity. This property of NaSnAs is useful for transverse thermoelectric (TE) cooling and thermal energy harvesting with a single TE leg. In this study, we used a Sn flux method followed by hot pressing to synthesize NaSnAs polycrystalline bulk samples. Seebeck coefficient measurements revealed n-type polarity along in-plane and p-type polarity along cross-plane directions over a temperature range of 300–520 K. This finding indicates that axis-dependent conduction polarity is conserved in polycrystalline NaSnAs bulk samples with a preferred orientation. A significantly low lattice thermal conductivity of 0.8 W/mK at 520 K was obtained because of phonon scattering caused by strong anharmonicity in the lattice vibration. First-principles calculation suggests that axis-dependent conduction polarity occurs where the Fermi level lies within the bandgap. Furthermore, we predict that high-TE performance can be achieved by optimizing the carrier concentration because of their characteristic pudding mold type band structure, which leads to the coexistence of a high density of states and group velocity.

Physical properties of Ce3+xRu4Sn13−x single crystals

Single crystals of ${\mathrm{Ce}}_{3+x}{\mathrm{Ru}}_{4}{\mathrm{Sn}}_{13\ensuremath{-}x}$ $(0.05\ensuremath{\le}x\ensuremath{\le}0.34)$, which adopt the cubic structure ($Pm\overline{3}n$, No. 223), have been grown with Sn flux. Thermodynamic and transport property measurements from single-crystal samples do not show any sign of magnetic ordering down to 1.8 K and indicate coexistence of the Kondo effect and crystalline electric field effect. The local minimum in the electrical resistivity and highly enhanced specific heat values at low temperatures characterize this family as a heavy fermion Kondo lattice system. A broad peak is observed at $\ensuremath{\sim}$3.5 K for $x=0.05$ in the specific heat and magnetic susceptibility, suggesting a significant Kondo contribution, and the peak disappears as $x$ increases. The evolution of physical properties of ${\mathrm{Ce}}_{3+x}{\mathrm{Ru}}_{4}{\mathrm{Sn}}_{13\ensuremath{-}x}$ compounds can be attributed to the nature of the individual Ce ions that occupy two inequivalent $2a$ and $6d$ crystallographic sites.

Evolution of Thermoelectric Properties in the Triple Cation Zintl Phase: Yb13–xCaxBaMgSb11 (x = 1–6)

The band structure of Yb14MgSb11 is tuned by substituting the more earth-abundant cations, Ca and Ba, on the four crystallographically distinct Yb sites (Yb13–xCaxBaMgSb11 (x = 1, 2, 3, 4, 5, 6)). Single crystals of composition Yb9.7(2)Ca3.85(5)Ba0.29(4)Mg1.13(3)Sb11.0(1) were grown from Sn flux revealing the cation site preferences. Magnetic measurements on this crystal show paramagnetic behavior consistent with the presence of ∼0.85 Yb3+. High-purity samples (>98%) with compositions close to nominal of Yb13–xCaxBaMgSb11 (x = 1–6) were prepared by ball milling and spark plasma sintering. The carrier concentration can be rationalized with the presence of Yb3+ for all samples and decreases as a function of x in a systematic fashion at room temperature and increases above ∼600 K for x = 3–6. The temperature dependence of the carrier concentration can be understood considering the electronic structure with a light and heavy band valence band contributing to the properties and suggests the involvement of a localized flat band or impurity state that is active with increasing amounts of Ca. The effect of temperature leads to sustained high Seebeck coefficients with low electrical resistivity arising from the transitioning of the light to heavy band with localization of carriers in the flat band or impurity state for Ca-rich compositions. Speed of sound measurements show that the lattice stiffens with increasing x. Despite the stiffening lattice, the thermal conductivity decreases until x = 3, 4 at which point it increases slightly. The x = 4 sample reaches a peak figure of merit (zT) of 1.32 at 1273 K while being 16% lighter by the molar mass compared to Yb14MnSb11 thereby providing a more power dense material.

Flux growth, mixed valence state and superconductivity of Sn4Sb3 intermetallic crystals

Single crystals of Sn4Sb3 with mm size have been obtained for the first time via a Sn flux method. Structural refinements confirm its trigonal structure with the centrosymmetric R3̄m space group. The unit cell consists of ordered [Sn–Sb–Sn–Sb–Sn–Sb–Sn] lamellae stacked along the c-axis, in which Sn is found to exhibit mixed valence states of 0 and 2+. Below 1.47 K, single crystalline Sn4Sb3 becomes a weakly coupled, fully gapped superconductor. In contrast to polycrystalline samples, the resistive transition of Sn4Sb3 crystals coincides well with the specific-heat jump, which supports that grain boundaries are responsible for the higher resistive Tc in the former case. Theoretical calculations show that the density of states at the Fermi level are mainly contributed by Sn and Sb 5p orbitals and almost unaffected by the spin-orbit interaction. Our study lays a foundation for experimental investigations of the predicted topological properties in this intermetallic compound.

Large Anisotropic Magnetocaloric Effect, Wide Operating Temperature Range, and Large Refrigeration Capacity in Single-Crystal Mn5Ge3 and Mn5Ge3/Mn3.5Fe1.5Ge3 Heterostructures.

At present, the studies on magnetocaloric properties are mainly based on polycrystalline materials, which is not enough to reveal and understand the origin of their magnetocaloric effect. In addition, finding new room temperature magnetocaloric materials is crucial to the development and application for room temperature magnetic refrigeration. Here, we report the magnetic transitions, magnetic anisotropy, and magnetocaloric properties of single-crystal Mn5Ge3 and Mn5Ge3/Mn3.5Fe1.5Ge3 heterostructures with six (100) surfaces and the [001] growth direction prepared using the Sn flux method. Mn5Ge3 (Mn3.5Fe1.5Ge3) undergoes a sharp paramagnetic-collinear ferromagnetic transition at 299 (332) K and weak collinear-noncollinear ferromagnetic transition at 65 (35) K. Owing to the distinct spin arrangements and magnetic moments of Mn5Ge3 and Mn3.5Fe1.5Ge3, the magnetic anisotropy of the single crystal is stronger than that of the heterostructure below 299 K. Moreover, a large anisotropic magnetocaloric effect, wide operating temperature range, and large refrigeration capacity near room temperature are obtained in these two materials, especially the magnetocaloric effect of the heterostructure presents a tablelike shape due to the adjacent paramagnetic-collinear ferromagnetic transitions of Mn5Ge3 and Mn3.5Fe1.5Ge3. Under 0-3 T, the maximum magnetic entropy change, operating temperature range, and refrigeration capacity of the single crystal (heterostructure) are 5.19 (2.96) J kg-1 K-1, 43 (57) K, and 223 (169) J kg-1 when H//c, respectively. These features make them candidates for room temperature magnetic refrigeration.

Growth Parameter Based Control of Cation Disorder in MgSnN2 Thin Films

MgSnN $$_2$$ thin films have been grown on yttria-stabilized zirconia substrates via plasma-assisted molecular beam epitaxy and analyzed using reflection high-energy electron diffraction, X-ray diffraction, optical transmission, and cathodoluminescence. By systematically varying the growth parameters, particularly the substrate temperature, Mg:Sn flux ratio, substrate, and nitrogen flow rate, we were able to achieve high quality films and control disorder in the cation sublattice. This control of disorder allows for the ability to adjust the band gap continuously over a wide range of values.

Computationally Guided Discovery of Axis-Dependent Conduction Polarity in NaSnAs Crystals

Most electronic materials exhibit a single dominant charge carrier type, either holes or electrons, along all crystallographic directions. However, there are a small number of compounds, mostly metals, that exhibit simultaneous p-type and n-type conduction behavior along different crystallographic directions. We demonstrate that the experimental discovery of semiconductors with this axis-dependent conduction polarity can be facilitated by identifying a large anisotropy of either the electron or hole effective masses (m*) or both, providing the electron and hole masses dominate along different crystallographic directions. We calculated the layered semiconductor NaSnAs to have a lower electron m* in-plane than the cross-plane and a very large hole m* in-plane and small hole m* cross-plane. We established the growth of >3 mm-sized NaSnAs crystals via Sn flux and confirmed the band gap to be 0.65 eV, in agreement with theory. NaSnAs exhibits p-type thermopowers cross-plane and n-type thermopowers in-plane, confirming that the large anisotropy in the effective mass at the band edges is an excellent indicator for axis-dependent conduction polarity. Overall, this work shows that the discovery of semiconductors with such a phenomenon can be accelerated by computationally evaluating the anisotropic curvatures of the band edges, paving the way for their future discovery and application.

Development and Understanding of Nb3Sn films for radiofrequency applications through a sample-host 9-cell cavity

Nb3Sn is a promising advanced material under development for superconducting radiofrequency cavities. Past efforts have been focused primarily on small development-scale cavities, but large, often multi-celled cavities, are needed for particle accelerator applications. In this work, we report on successful Nb3Sn coatings on Nb in a 1 m-long 9-cell Nb sample-host cavity at Fermilab. The geometry of the first coating with only one Sn source made it possible to study the influence of Sn flux on the microstructure. Based on these results, we postulate a connection between recently observed anomalously large thin grains and uncovered niobium spots observed in the past by other authors (Trenikhina et al 2018 Supercond. Sci. Technol. 32 015004). A phenomenological model to explain how these anomalously large grains could form is proposed. This model is invoked to provide possible explanations for literature results from several groups and to guide key process parameters to achieve uniform vapor-diffusion coatings, when applied to complex structures as the multi-cell cavity under study.

Development of a flux-film-coated sputtering (FFC-sputtering) method for fabricating c-axis oriented AlN film

In this study, we developed a novel growth method named “Flux-Film-Coated (FFC) sputtering.” In this method, nitrogen radicals were supplied to the Al–Sn flux at around 600 °C followed by the deposition of an Al–Sn metal film on a sapphire substrate as flux, which resulted in the growth of high-quality AlN films. The nitrogen radical, which is the source of nitrogen for the growth of AlN, was generated by the radio frequency plasma in a nitrogen atmosphere. Using a zirconia target in the plasma generation process, nitrogen radicals were easily generated because the zirconia was not etched in a pure nitrogen atmosphere, which enabled us to fabricate the AlN film using the flux method in the sputtering chamber in a single step. The crystallinity of the synthesized AlN determined using the FFC-sputtering method was remarkably improved when compared with that of the AlN film deposited using the reactive sputtering method.

Refine Intervention: Characterizing Disordered Yb0.5Co3Ge3

Single crystals of the ternary Yb0.5Co3Ge3 have been grown out of molten Sn flux and characterized by single crystal and synchrotron powder X-ray diffraction. Yb0.5Co3Ge3 adopts a hybrid YCo6Ge6/Co...