Ni Sn System Research Articles

A first-principles study of the mechanical and physical properties of Ni3Snx intermetallic compounds for high-temperature power device packaging

Ni–Sn intermetallic compound is a highly promising high-temperature packaging material for power devices, and it is very necessary to understand and control the physical and mechanical properties of Ni–Sn intermetallic compounds(IMCs). However, the current research mainly focuses on the rapid preparation of such packaging solder joints, and there is little research on the microstructure, physical and mechanical properties of alloys. In this study, the first-principle and quasi-harmonic Debye models were used to analyze the mechanical characteristics, electronic structure, thermal conductivity, and linear expansion coefficient of three IMCs (Ni3Sn, Ni3Sn2, and Ni3Sn4) of the Ni–Sn system. The results show that Ni3Sn has the highest modulus and fracture toughness and has the best elastic match with Ni. The welded joints of Ni/Ni3Sn/Ni structures can effectively prevent the generation of microcracks under the stress field. They're all mixed-bond compounds, according to the results of electronic structure simulations, and Ni3Sn4 has the most ionic and covalent bonds, so its fracture toughness is the lowest and its anisotropy tendency is the most significant. The thermal conductivity of Ni3Sn is the highest, the linear expansion coefficients of Ni3Sn and Ni3Sn4 are not significantly different, and they match well with the linear expansion coefficients of Ni.

Effect of ultrafine microstructure on interdiffusion-driven phase transformations in Ni-Sn sandwich diffusion couples

Solid-state diffusion in materials is greatly influenced by microstructural features such as grain boundaries, dislocations, and second phase particles. However, a systematic investigation of structure-kinetics correlation during interdiffusion is largely missing. Herein, a novel sandwich diffusion couple approach was utilized to demonstrate the effects of microstructure on interdiffusion-driven phase formation in the Ni-Sn system. Pure Ni samples were prepared by cold rolling (CR) and spark plasma sintering (SPS) with different microstructures. Two sandwich diffusion couples were prepared– a) NiAM/Sn/NiCR and b) NiCR/Sn/NiSPS, for phase growth analysis at each interface after annealing at 200 °C for 96 h. The intermetallic phase Ni3Sn4 formed at the NiAM/Sn, NiCR/Sn, and NiSPS/Sn interfaces had the thickness of 6, 14, and 41 µm, respectively, consistent with larger parabolic growth constant for the NiSPS/Sn interfaces. The enhanced kinetics at the SPS interface could be attributed to the presence of ultrafine-grained (UFG) (∼320 nm) microstructure dominated by high-angle boundaries.

Accelerated phase growth kinetics during interdiffusion of ultrafine-grained Ni and Sn

The phase growth is investigated during the interdiffusion of an ultra-fine grained Ni (UFG) (grain size, d ∼ 320 nm) and coarse-grained Sn diffusion couple in the temperature range of 175–215 °C. The UFG Ni was produced through spark plasma sintering (SPS) of ball-milled Ni powder. Formation of only Ni3Sn4 intermetallic phase is observed, as confirmed by electron probe microanalysis (EPMA), micro-x-ray diffraction (XRD), and Transmission Kikuchi Diffraction (TKD) measurements. Using the CALPHAD approach, the driving forces for the formation of possible intermetallic phases in the Ni-Sn system were estimated and the highest value was found for Ni3Sn4, which matches the experimental observations. Time-dependent measurements at 200 °C revealed an acceleration in the growth (∼2 orders of magnitude) of Ni3Sn4 compared to the scenario prevalent in the coarse-grained (CG) Ni/Sn diffusion couple. This is reflected in the calculated integrated diffusivities for the UFG-Ni/Sn diffusion couple. The accelerated phase growth kinetics are attributed to the increased fraction of grain boundaries (GBs) in the UFG-Ni, which leads to an increased contribution of GB diffusion to the overall diffusion flux. The formation of Ni3Sn4 at GB was further ascertained using correlative microscopy strategy including transmission electron microscopy, transmission Kikuchi diffraction and scanning transmission electron microscopy.

Identifying the effect of Ni solubility on the thermoelectric properties of HfNiSn-based half-Heuslers

Phase diagrams provide important guidance for the optimal design of thermoelectric materials. Previous studies demonstrated a specific solubility of Ni atoms in TiNiSn and ZrNiSn, which can impede phonon transport and regulate the electronic band structure. But the thermodynamic investigation and the effect of Ni content on thermoelectric properties for the HfNiSn system are absent. In this work, we constructed an isothermal section phase diagram of the Hf-Ni-Sn ternary system at 1173 K and determined the solubility of Ni in the vacant position to be 0.04 < x < 0.16. At this temperature profile, the stoichiometric ratio HfNiSn is located in the two-phase region of HfNi1+xSn + Sn when it is in equilibrium, and the homogeneity region may be broken by the process of ball milling and sintering. Calculation results indicate that the excess-Ni in HfNiSn will generate impurity levels in the forbidden band and localized phonon modes above the acoustic branch. The intermediate-Heusler phase formed by extra Ni atoms can work as a phonon scattering center and reduce the lattice thermal conductivity near room temperature, but the Sn impurities generated by the disrupted thermal equilibrium will neutralize this effect at high temperatures. Overall, the impact of the Ni-rich environment on HfNiSn-based half-Heusler is very different from that of alloys TiNiSn and ZrNiSn, which is of great significance for the comprehensive understanding of (Ti, Zr, Hf)NiSn system.

Thermodynamic Re-assessment of the Ag–Ni–Sn system

The ternary Ag–Ni–Sn and the constituent binary Ag–Sn and Ni–Sn systems were critically re-assessed considering the available experimental data based on the CALPHAD (CALculation of PHAse Diagram) method. Thermodynamic descriptions of both Ag–Sn and Ni–Sn systems were obviously improved in comparison with the previous reports, especially in the heat capacity of Ag3Sn and enthalpy of mixing of Ag–Sn liquid, as well as the homogeneity range of Ni3Sn4 and the temperature dependent enthalpy of mixing of Ni–Sn liquid. Based on the updated thermodynamic description for the binary systems, a set of self-consistent thermodynamic parameters for the Ag–Ni–Sn system was then obtained. Comprehensive comparisons between the calculated results and experimental data on thermodynamic properties, isothermal and vertical sections as well as invariant reactions indicated the reliability and accuracy of the present thermodynamic parameters. Liquidus projection and the scheil reaction scheme of the entire composition range were also presented correspondingly.

Development of atomic mobility with quantified uncertainties directly from concentration profiles: a demo in fcc Cu–Ni–Sn system

Development of atomic mobility with quantified uncertainties directly from concentration profiles: a demo in fcc Cu–Ni–Sn system

Thermodynamic descriptions of the binary Ni–Sn and ternary Cu–Ni–Sn systems over entire composition range: A revisit

In this study, the phase equilibria of the Cu–Ni–Sn ternary system reported in the literature were critically reviewed and the discrepancies between the results from different sources were clarified. The thermodynamic parameters of the sub-binary Ni–Sn system were updated using the CALculation of PHAse Diagram (CALPHAD) approach yielding significant improvements in the description of Fcc phase boundary. Besides, the artificial miscibility gap in Ni–Sn liquid phase obtained in the previous assessment was successfully removed. Subsequently, a set of self-consistent thermodynamic parameters for the Cu–Ni–Sn ternary system over the whole composition range was systematically optimized by considering the reviewed experimental information together with the updated thermodynamic description for the Ni–Sn binary system. Comprehensive comparison of the calculated and reported thermodynamic properties as well as isothermal and vertical sections shows that the experimental information is satisfactorily reproduced by the present modeling, further validating the thermodynamic descriptions developed in this work.

A low-temperature sealing method for metal-supported oxide fuel cell applications: Ni–Sn transient liquid phase bonding

A low-temperature sealing approach, transient liquid phase bonding with Ni–Sn system, was employed to seal metal-supported solid oxide fuel cell (MS-SOFC) components in this study. The Ni layer was prefabricated on the ferritic stainless steels by electroplating firstly, and then were vacuum annealed to enhance the bonding between the Ni coating and the steel substrate. Afterward, the Ni coated steels were transient liquid phase bonded using a thin interlayer of pure Sn. Effects of bonding temperature (250–400 °C) and holding time (10–60 min) on the interface of joints were investigated. The interfacial microstructure of joints was observed by the scanning electron microscope and the transmission electron microscope. A joint with full intermetallic compounds (IMCs) of Ni3Sn4 and Ni3Sn2 were formed at 400 °C/60 min. These Ni–Sn IMCs were all stable up to 794.5 °C, ensuring that the joint with full IMCs microstructure can be performed at the operating temperature of ∼600 °C for MS-SOFC. Furthermore, the residual Ni coating can also be served as a protective layer for the stack.

Mechanochemical synthesis of the NiSn, CuSn bimetallic and NiCuSn trimetallic nanocomposites using various types of additives

Ni-Cu-Sn nanocomposite was prepared for the first time, in the mechanochemical way complementing with the investigation of milled Cu-Sn and Ni-Sn systems using grinding additives. Several chemicals were examined like NaCl, PVP, CTAB, SDS, oleylamine, n-heptane, ethylene and polyethylene glycol. X-ray diffractometry attested the varying effects of the additives on the quality and quantity of the milling end-products: in several cases complete or partial mechanical alloying occurred, while in some instances, the segregation of the starting materials were also observed verified by spatially-resolved energy dispersive X-ray analysis. Dynamic light scattering measurements revealed the efficacy of additive amounts used on particle size reduction and size distribution of the milled bimetallic and trimetallic solids. For the Ni-Cu-Sn nanocomposites, the average solvodynamic diameters varied in the range 180–700 ​nm with 0.21–0.48 polydispersity values. The application of CTAB and PVP resulted in aggregated nanoparticles under 100 ​nm size in significant amounts verified by the transmission electron microscopy images. The analysis of the surface plasmon resonance bands of the nanocomposites indicated the presence of the Cu(I) oxide phase, while the calculated textural parameters increased up to 5 and 24 ​m2/g and 0.01–0.05 ​cm3/g specific surface area and total pore volume values, respectively, compared to the 0.8 ​m2/g and 0.002 ​cm3/g of the milling in the absence of additives.

A novel approach to calculate diffusion matrix in ternary systems: Application to Ag–Mg–Mn and Cu–Ni–Sn systems

Diffusion behavior is of fundamental importance in material science and engineering. As a result, extensive attention has been paid to develop methodologies for obtaining the composition-dependent interdiffusivities. The present work proposed a novel approach with two steps to extract the interdiffusion coefficients from a single ternary diffusion couple. The concept of basis function is introduced, and this novel method is based on the utilization of both finite element method and optimization algorithm. Utilizing eight groups of diffusion couples together with electron probe microanalysis technique, the composition-dependent interdiffusion coefficients in fcc Ag–Mg–Mn alloys at 973 and 1073 K were determined via both the present method and Matano-Kirkaldy method. A home-made code is written to implement the novel numerical approach. The obtained interdiffusion coefficients based on the present method agree with the reliable ones from the Matano-Kirkaldy method better than previous methods for fcc Ag–Mg–Mn alloys in the present work as well as fcc Cu–Ni–Sn alloys from the literature, especially for the main interdiffusivities. In most cases, the presently computed main interdiffusivities by means of the composition-dependent diffusivities agree with the reliable ones from the Matano-Kirkaldy method within 50%. Besides, the sign of cross interdiffusivities using this novel method is usually the same as that from the Matano-Kirkaldy method. Such a high calculation precision and efficiency cannot be obtained using previous methods.

On the Phase Separation in n-Type Thermoelectric Half-Heusler Materials.

Half-Heusler compounds have been in focus as potential materials for thermoelectric energy conversion in the mid-temperature range, e.g., as in automotive or industrial waste heat recovery, for more than ten years now. Because of their mechanical and thermal stability, these compounds are advantageous for common thermoelectric materials such as BiTe, SiGe, clathrates or filled skutterudites. A further advantage lies in the tunability of Heusler compounds, allowing one to avoid expensive and toxic elements. Half-Heusler compounds usually exhibit a high electrical conductivity , resulting in high power factors. The main drawback of half-Heusler compounds is their high lattice thermal conductivity. Here, we present a detailed study of the phase separation in an n-type Heusler materials system, showing that the TiZrHfNiSn system is not a solid solution. We also show that this phase separation is key to the thermoelectric high efficiency of n-type Heusler materials. These results strongly underline the importance of phase separation as a powerful tool for designing highly efficient materials for thermoelectric applications that fulfill the industrial demands of a thermoelectric converter.

Compositional partitioning during the spinodal decomposition in Cu–Ni–Sn alloy

Spinodal decomposition in Cu–9.4at%Ni–3.1at%Sn alloy was elucidated with the new insight from the experimental EXAFS analysis supported by ab initio total energy calculations suggesting the strong influence of the first near-neighbour atoms. Enthalpy of mixing was calculated for all crystallographically unique first near-neighbour configurations and finally an average positive enthalpy of mixing of 1604 J/mol was obtained. Combination of ab initio results, XRD and EXAFS analysis indicate that one of the daughter phase becomes rich in Ni and Sn than the other phase; in contrary to the earlier proposition that Cu/Ni ratio remains constant in both daughter phases. It is also shown that the present thermodynamic description requires further refinement to extend the miscibility gap towards lower Ni content in Cu–Ni–Sn system.

Interpreting the Combustion Process for High-Performance ZrNiSn Thermoelectric Materials.

The ZrNiSn alloy, a member of the half-Heusler family of thermoelectric materials, shows great potential for mid-to-high-temperature power generation applications due to its excellent thermoelectric properties, robust mechanical properties, and good thermal stability. The existing synthesis processes of half-Heusler alloys are, however, rather time and energy intensive. In this study, single-phase ZrNiSn bulk materials were prepared by self-propagating high-temperature synthesis (SHS) combined with spark plasma sintering (SPS) for the first time. The analysis of thermodynamic and kinetic processes shows that the SHS reaction in the ternary ZrNiSn alloy is different from the more usual binary systems. It consists of a series of SHS reactions and mass transfers triggered by the SHS fusion of the binary Ni-Sn system that eventually culminates in the formation of single-phase ternary ZrNiSn in a very short time, which reduced the synthesis period from few days to less than an hour. Moreover, the nonequilibrium feature induces Ni interstitials in the structure, which simultaneously enhances the electrical conductivity and decreases the thermal conductivity, which is favorable for thermoelectric properties. The maximum thermoelectric figure of merit ZT of the SHS + SPS-processed ZrNiSn1-xSbx alloy reached 0.7 at 870 K. This study opens a new avenue for the fast and low-cost fabrication of half-Heusler thermoelectric materials.

Site occupancy, composition and magnetic structure dependencies of martensitic transformation in Mn2Ni1 + xSn1−x

A delicate balance between various factors such as site occupancy, composition and magnetic ordering seems to affect the stability of the martensitic phase in . Using first-principles DFT calculations, we explore the impacts of each one of these factors on the martensitic stability of this system. Our results on total energies, magnetic moments and electronic structures upon changes in the composition, the magnetic configurations and the site occupancies show that the occupancies at the 4d sites in the inverse Heusler crystal structure play the most crucial role. The presence of Mn at the 4d sites originally occupied by Sn and its interaction with the Mn atoms at other sites decide the stability of the martensitic phases. This explains the discrepancy between the experiments and earlier DFT calculations regarding phase stability in NiSn. Our results qualitatively explain the trends observed experimentally with regard to martensitic phase stability and the magnetisations in Ni-excess, Sn-deficient NiSn system.

Solid–state diffusion–controlled growth of the intermediate phases from room temperature to an elevated temperature in the Cu–Sn and the Ni–Sn systems

The solid–state growth of intermediate phases in the Cu–Sn and Ni–Sn systems is investigated in the temperature range of room temperature to an elevated temperature. In the Cu/Sn diffusion couples, Cu6Sn5 and Cu3Sn grow at temperatures ≥ 100 °C and only the Cu6Sn5 phase is found at lower temperatures. The integrated interdiffusion coefficients are estimated in the temperature range of 125–215 °C because of the observation of parabolic growth. The activation energies are estimated to be 64±4 and 75±6 kJ/mol for Cu3Sn and Cu6Sn5, respectively. In the Ni/Sn diffusion couples, only Ni3Sn4 grows at higher temperatures. At 50–100 °C, metastable NiSn4 phase is found along with an equilibrium Ni3Sn4 phase. At room temperature, only the metastable NiSn4 phase is found. The activation energy for the integrated interdiffusion coefficient of Ni3Sn4 is estimated as 71.6±5.3 kJ/mol, which is similar to the values estimated in the Cu–Sn system. The growth rate of the product phases, for electroplated couples, is found to be a little higher in the Ni–Sn system as compared to the Cu–Sn system. During storage at room temperature and service at elevated temperatures, the phases in the Ni–Sn system have comparable growth rate when compared to the same in Cu–Sn system.

Phase separation in the half-Heusler thermoelectric materials (Hf,Ti,Zr)NiSn

The phase diagram of the pseudoternary (Hf,Ti,Zr)NiSn system is of interest for the selection of the compositions and for the prediction of the stability of the final material prior to measuring its thermoelectric properties. However, a review of the experimental data shows that it is difficult to obtain stable and acceptable alloys. To overcome this difficulty we have performed ab-initio calculations to predict the phase separations in the half Heusler phase. Our calculations are consistent with the experimental data and we obtain the evolution of the solid-solution from 500 to 1300K the temperature range of interest of these materials.

Interaction between solid nickel and a tin–indium eutectic melt, and the nature of eutectic alloys

Structural transformations during reactions between nickel and an indium–tin eutectic melt are studied via the diffraction of high-energy synchrotron radiation. It is shown that InNi intermetallic compound is the first to form after melting. No phases belonging to a Ni–Sn system are observed. A hypothesis concerning the nanocluster structure of the eutectic melt is proposed: Structural formations with forbidden five-fold, seven-fold, and higher-order rotational axes of symmetry lie at the heart of nanosized clusters.

Unraveling Self‐Doping Effects in Thermoelectric TiNiSn Half‐Heusler Compounds by Combined Theory and High‐Throughput Experiments

The control of the carrier concentration is a key topic in the optimization of the thermoelectric power factor. It depends intricately on the defect chemistry of a host phase (here: TiNiSn) and the boundary conditions set by competing phases. The large impact of a slight off‐stoichiometry in the intermetallic half‐Heusler phase TiNiSn makes combinatorial techniques ideally suited for systematic optimization of its thermoelectric performance. In this work, computational thermochemistry, combinatorial synthesis, and high‐throughput characterization are combined to obtain a complete map of the thermoelectric power factor for the Ti–Ni–Sn system. The role of the chemical potential of the constituents in determining the detailed nonstoichiometric composition of the intermetallic half‐Heusler phase TiNiSn is elucidated. This work not only confirms the assumption of a large phase‐width in terms of Ni surplus but also demonstrates that TiNiSn phases with a relatively large Ti surplus can be produced. This can serve as a new route for achieving high carrier concentrations by self‐doping in the ternary system Ti–Ni–Sn. The defect thermochemistry calculations for the carrier concentration are in excellent agreement with the experimental results. The findings of this work suggest new ways of improving the thermoelectric performance of half‐Heusler phases such as TiNiSn.

First-principle and molecular dynamics calculations for physical properties of Ni–Sn alloy system

The structural, elastic, vibrational and thermodynamic properties of binary Ni–Sn compounds are investigated by first-principle (FP) calculations. A set of modified embedded atom method (MEAM) potential for Ni–Sn system is proposed on the basis of the FP energy–volume relationships for the three compounds hP8-Ni3Sn, oP20-Ni3Sn2 and mC14-Ni3Sn4. The polycrystalline elastic properties of Ni–Sn compounds generally decrease with the increase of Sn atom fractions, and all of the isotropic intermetallics exhibit some extent of intrinsic ductility. Among all the structures, oP20-Ni3Sn2 has the highest degree of isotropy, whereas the others show different degrees of anisotropy. The high temperature phase cF16-Ni3Sn is both mechanically and dynamically unstable at ambient condition. By considering the lattice vibrations under quasiharmonic phonon or Debye approximation, the thermodynamic properties of Ni–Sn compounds such as the enthalpies and specific heats can be well predicted from FP or MEAM calculations as well as the finite temperature molecular dynamics simulations. Furthermore, the high temperature properties such as the surface tensions of Ni–Sn alloys can also be calculated from the MEAM potential.

Electronic structure of Zr–Ni–Sn systems: role of clustering and nanostructures in half-Heusler and Heusler limits

Half-Heusler and Heusler compounds have been of great interest for several decades for thermoelectric, magnetic, half-metallic and many other interesting properties. Among these systems, Zr–Ni–Sn compounds are interesting thermoelectrics which can go from semiconducting half-Heusler (HH) limit, ZrNiSn, to metallic Heusler (FH) limit, ZrNi2Sn. Recently Makongo et al (2011 J. Am. Chem. Soc. 133 18843) found that dramatic improvement in the thermoelectric power factor of HH can be achieved by putting excess Ni into the system. This was attributed to an energy filtering mechanism due to the presence of FH nanostructures in the HH matrix. Using density functional theory we have investigated clustering and nanostructure formation in ZrNi1+xSn (0 ⩽ x ⩽ 1) systems near the HH (x = 0) and FH (x = 1) ends and have found that excess Ni atoms in HH tend to stay close to each other and form nanoclusters. On the other hand, there is competing interaction between Ni-vacancies occupying different sites in FH which prevents them from forming vacancy nanoclusters. Effects of nano-inclusions on the electronic structure near HH and FH ends are discussed.