Magnetic,electronic and transport properties of the Ce3Ag4X4 (X=Ge,Sn) compounds

The work presents results of magnetometric, transport, XPS and neutron diffraction measurements performed on polycrystalline samples of Ce₃Ag₄X₄ (X=Ge, Sn). The X-ray and neutron diffraction data indicate that these compounds crystallize in an orthorhombic structure of the Gd₃Cu₄Ge₄-type. The magnetometric data reveal a ferromagnetic-like behaviour below 10 K in the case of Ce₃Ag₄Ge₄ and a weak antiferromagnetic-like maximum at 9 K for Ce₃Ag₄Sn₄. The neutron diffraction data do not evidence magnetic ordering in any of the two compounds. Temperature variations of the electrical resistivity and thermoelectric power suggest their metallic character. The Ce 3d X-ray photoemission spectra show that both compounds are mixed valence systems. Analysis of the f² peak weight using the Gunnarsson–Schönhammer theory suggests a hybridization constant of 169 meV for Ce₃Ag₄Ge₄ and 82 meV for Ce₃Ag₄Sn₄. The valence band spectra are dominated by the Ag 4d states contributions. Broad and very weak peaks extending between 0 and 4 eV correspond to the Ce 5d6s² states.     

Synthesis,structure, and magnetic property of hexagonal perovskite Ba5Sn1.1Mn3.9O15

A new compound Ba₅Sn_1.1Mn_3.9O₁₅ has been synthesized at 1300 °C by solid-state reaction. The structure was characterized by X-ray, electron and neutron diffraction methods. Ba₅Sn_1.1Mn_3.9O₁₅ crystallizes in hexagonal space group P6₃/mmc with a = 5.717 Å and c = 23.534 Å. The magnetic measurement reveals that Ba₅Sn_1.1Mn_3.9O₁₅ has a spin glass transition at 7 K.     

A new phase in stoichiometric Cu6Sn5

The intermetallic compound Cu₆Sn₅ is a significant microstructural feature of many electronic devices where it is present at the solder–substrate interfaces. The time- and temperature-dependent thermomechanical properties of Cu₆Sn₅ are dependent on the nature and stability of its crystal structure, which has been shown to exist in at least four variants (η, η′, η⁶ and η⁸). This research details an additional newly identified monoclinic-based structure in directly alloyed stoichiometric Cu₆Sn₅ using variable-temperature synchrotron X-ray diffraction (XRD) and transmission electron microscopy. The phase is associated with a departure from the equilibrium temperature of the polymorphic monoclinic–hexagonal transformation temperature. The new monoclinic phase can be treated as a modulation of four η⁸-Cu₅Sn₄ unit cells plus one η′-Cu₆Sn₅ unit cell. It has been labeled as η⁴⁺¹ and has cell parameters of a = 92.241 Å, b = 7.311 Å, c = 9.880 Å and β = 118.95° determined from electron diffraction patterns. The XRD results could be fitted well to a Rietveld refinement using the new crystal parameters.     

The structure and magnetic properties of Th4Mn13Sn5

We have synthesized the new intermetallic compound Th₄Mn₁₃Sn₅: it crystallizes with the Th₄Fe₁₃Sn₅ type structure, tetragonal tP44, space group P4/mbm, a = 8.423(1) Å and c = 11.972(2) Å. The Mn ions in Th₄Mn₁₃Sn₅ order ferro/ferrimagnetically around 110 K. A low magnetization of 0.13 μ_B/Mn at 4.2 K in a field of 70 kOe and a large fractional temperature independent contribution to susceptibility in the paramagnetic regime suggest an appreciable itinerancy of the Mn 3-d state in this compound. The electrical resistivity shows an anomaly at the magnetic transition and varies as T² below 30 K with a coefficient of 8.38 × 10^?3 μΩ cm/K². The low temperature heat capacity data furnish a Sommerfeld coefficient of 16.9 mJ/g atom K². In the course of present work we have also identified the ThMn_0.2Sn₂ phase which adopts a defective CeNiSi₂ type structure, orthorhombic oS16, space group Cmcm with a = 4.476(2) Å, b = 17.059(3) Å and c = 4.398(1) Å.     

Morphologies,orientation relationships and evolution of Cu6Sn5 grains formed between molten Sn and Cu single crystals

The morphologies and orientation relationships of Cu₆Sn₅ grains formed between Sn and (0 0 1), (0 1 1), (1 1 1) and (1 23) Cu single crystals under liquid- and solid-state aging conditions were systematically investigated. The regular prism-type Cu₆Sn₅ grains formed on (0 0 1) and (1 1 1) Cu single crystals are elongated either along two perpendicular directions or along three preferential directions with an angle of 60° between each pair of directions. The orientation relationships between Cu and Cu₆Sn₅ lattice structures were determined by electron backscatter diffraction and were explained in terms of their minimum misfit. However, on (0 1 1) and (1 2 3) Cu single crystal surfaces, the Cu₆Sn₅ grains were mainly scallop-type, with only a few regular prism-type grains. Furthermore, the regular prism-type Cu₆Sn₅ grains will change into scallop-type after long reflow or aging times. Meanwhile it is considered that the growth of the scallop-type grains is supplied by two fluxes: the flux of the interfacial reaction and the flux of ripening. However, the growth of the prism-type grains is only supplied by the flux of the interfacial reaction. The kinetics of IMCs growth between Sn and Cu single crystals was also investigated.     

An investigation of the structural dynamics in the fast ionic conductor Cu2−δSe using neutron scattering

Energy resolved neutron diffraction measurements were performed on Cu_1.75Se and Cu_1.98Se samples for both α- and β-phases. In-situ measurements of the Cu_1.98Se compound during heating show that the β–α phase transition takes place at 420 K and has noticeable temperature hysteresis. In addition to Bragg reflections, the diffraction patterns of the α-Cu_1.75Se at RT and α-Cu_1.98Se at 435 K samples taken in conventional two-axis geometry show a broad maximum related to diffuse scattering. This diffuse background is suppressed in the energy resolved experiment which indicates a strong contribution from inelastic scattering coming from correlated thermal displacements of the ions in the super-ionic phase. On the other hand, the diffraction pattern of the non super-ionic β-phase shows only minor differences between spectra measured with and without the analyser crystal.     

The 260 °C phase equilibria of the Sn–Sb–Cu ternary system and interfacial reactions at the Sn–Sb/Cu joints

The isothermal section of the Sn–Sb–Cu ternary system at 260 °C has been determined in this study by experimental examination. Experimental results show no existence of ternary compounds in the Sn–Sb–Cu system. An extensive region of mutual solubility existing between the two binary isomorphous phases, Cu₃Sn and Cu₄Sb, was determined and labeled as δ. Intermetallic compounds (IMCs) Cu₂Sb, SbSn, and Cu₆Sn₅ are in equilibrium with the δ solid solution. Up to about 6.5 at.%Sb can dissolve in the Cu₆Sn₅ phase, and the solubility of Sn in the Cu₂Sb is approximately 6.2 at.%. Each of the Sb and SbSn phases has a limited solubility of Cu. Only one stoichiometric compound, Sb₂Sn₃, exists. Besides phase equilibria determination, the interfacial reactions between the Sn–Sb alloys and Cu substrates were investigated at 260 °C. Sb was observed to be present in the Cu₆Sn₅ and δ phases, and Sb did not form Sn–Sb IMCs in the interfacial reactions. Moreover, the addition of up to 7 wt% of Sb into Sn does not significantly affect the total thickness of IMC layers. It was found that the phase formations in the Sn–Sb/Cu couples are very similar to those in the Sn/Cu couples.     

Magnetic,electronic and transport properties of RAg2Ge2 (R=Pr,Nd) compounds

Magnetization, magnetic susceptibility, electrical resistivity, thermoelectric power, neutron diffraction and X-Ray photoemission spectroscopy measurements were performed on polycrystalline samples of PrAg₂Ge₂ and NdAg₂Ge₂, both crystallizing with a tetragonal structure of the ThCr₂Si₂-type. The data indicate that both compounds order magnetically at low temperatures, PrAg₂Ge₂ at 12 K and NdAg₂Ge₂ at 2 K. Neutron diffraction data for the latter indicate antiferromagnetic collinear structure described by the propagation vector k=(½, 0, ½) at 1.5 K. Both compounds exhibit metallic-like electrical behavior. The X-Ray photoemission data indicate that the valence bands are formed mainly by the Ag 4d bands. The spin-orbit splitting values determined from the XPS spectra of Pr and Nd, 3d_5/2 and 3d_3/2, equal 20.5 eV for the Pr compound and 22.7 eV for the Nd compound. The analysis of these spectra performed on the basis of the Gunnarsson-Schönhammer model indicates a weak hybridization of the 4f electrons with the conduction band.     

Intermetallic compounds in the M–Cu–Sn systems with M = Eu,Sr, Ba

Several samples were prepared in the title systems, starting from the elements sealed under argon in Ta crucibles, melting in an induction fornace and annealing at 823 K. Six ternary phases were found: EuCu₂Sn₂, a = 11.100 (3), b = 4.307 (1), c = 4.824 (1) Å, β = 108.88 (1)°, and SrCu₂Sn₂, a = 11.197 (4), b = 4.322 (2), c = 4.859 (1) Å, β = 108.43 (1)°, C2/m, CaCu₂Sn₂-type, closely related to the BaAl₄ structure; Sr₃Cu₈Sn₄, a = 9.3280 (2), c = 7.8826 (4) Å, P6₃mc, Nd₃Co₈Sn₄-type, ordered variant of the BaLi₄-type; SrCu₄Sn₂, a = 8.176 (1), c = 7.799 (1) Å, I4/mcm, CaNi₄Sn₂-type; SrCu₉Sn₄, a = 8.663 (1), c = 12.457 (2) Å, and BaCu₉Sn₄, a = 8.717 (1), c = 12.545 (2) Å, I4/mcm, LaFe₉Si₄-type, ordered variant of the NaZn₁₃ structure. The structure of the first compound was refined by the Rietveld method, while single crystal data were used for the others. Some remarks are given on the crystal chemistry of the encountered and related structure types.     

Magnetic structure of Er6Ni2Sn

The crystallographic and magnetic structures of Er₆Ni₂Sn have been determined at low temperatures using neutron powder diffraction. It has been found that this system orders antiferromagnetically (AF) below T_N = 17 K. Data taken at low temperatures and analyzed using symmetry group analysis suggest that Er₆Ni₂Sn forms a complex non-collinear commensurate AF structure with strongly reduced Er magnetic moments. The reason for the reduced moments is unclear and needs further studies. The magnetic phases below 7 K and in the temperature range 7–17 K differ only in the Er magnetic moment magnitudes and in the angle that the Er moments at the 8l site make with the c-axis. The extra reflections present in the powder diffraction patterns suggest presence of a secondary phase. The temperature evolution of the powder pattern indicates that the secondary phase orders AF at 35 K.     

Photo-induced magnetization in copper(II) octacyanomolybdate(IV)

The photomagnetic effect of the mixed-valence compound Cu₂^II[Mo^IV(CN)₈]·7.6H₂O (Cu^II; 3d⁹, S=1/2, Mo^IV; 4d², S=0) (1) was investigated. The UV–VIS spectra showed the intervalence transfer (IT) band between Mo^IV–CN–Cu^II and Mo^V–CN–Cu^I around 500 nm. When the paramagnetic compound 1 was irradiated by a filtered blue light (400–430 nm, 3 mW/cm²) of a Xe lamp at 5 K, the irradiated sample exhibited a spontaneous magnetization with a Curie temperature of 17 K. By annealing the irradiated sample above 200 K, the magnetic property of this sample returned to the initial state. This photo-induced magnetization is explained by the following mechanism. The excitation of the IT band causes the electron transfer from Mo^IV (S=0) to Cu^II (S=1/2), producing a mixed-valence isomer of Mo^V (S=1/2)–CN–Cu^I (S=0). However, half of the copper ions remain as Cu^II ions due to the stoichiometric limitation and hence the irradiated 1 is expressed as Cu^ICu^II[Mo^V(CN)₈]·7.6H₂O. The unpaired electrons on Mo^V (S=1/2) ions and those on Cu^II (S=1/2) ions in the irradiated compound interact ferromagnetically, giving rise to the spontaneous magnetization.     

Investigation of diffusion and electromigration parameters for Cu–Sn intermetallic compounds in Pb-free solders using simulated annealing

An efficient numerical method was developed to extract the diffusion and electromigration parameters for multi-phase intermetallic compounds (IMC) formed as a result of material reactions between under bump metallization (UBM) and solder joints. This method was based on the simulated annealing (SA) method and applied to the growth of Cu–Sn IMC during thermal aging and under current stressing in Pb-free solder joints with Cu-UBM. At 150 °C, the diffusion coefficients of Cu were found to be 3.67 × 10¹⁷ m² s⁻¹ for Cu₃Sn and 7.04 × 10¹⁶ m² s⁻¹ for Cu₆Sn₅, while the diffusion coefficients of Sn were found to be 2.35 × 10¹⁶ m² s⁻¹ for Cu₃Sn and 6.49 × 10¹⁶ m² s⁻¹ for Cu₆Sn₅. The effective charges of Cu were found to be 26.5 for Cu₃Sn and 26.0 for Cu₆Sn₅, and for Sn, the effective charges were found to be 23.6 for Cu₃Sn and 36.0 for Cu₆Sn₅. The SA approach provided substantially superior efficiency and accuracy over the conventional grid heuristics and is particularly suitable for analyzing many-parameter, multi-phase intermetallic formation for solder systems where quantitative deduction for such parameters has seldom been reported.     

Large magnetocaloric effect in a wide temperature range induced by two successive magnetic phase transitions in Ho2Cu2Cd compound

The magnetic and magnetocaloric properties of Ho₂Cu₂Cd compound have been studied. The compound reveals two successive magnetic phase transitions at 30 K and 15 K which are corresponding to the paramagnetic to ferromagnetic transition and a spin reorientation, respectively. Two successive magnetic transitions in Ho₂Cu₂Cd resulting two peaks in the temperature dependence of magnetic entropy change curves, −ΔS_M (T). Two peaks are partly overlapped and induced a large MCE in a wide temperature range, i. e., large refrigerant capacity (RC) and relative cooling power (RCP). For a magnetic field change of 0–7 T, the values of maximal −ΔS_M, RC and RCP are 25.1 J/kg K, 527 J/kg and 732 J/kg for Ho₂Cu₂Cd, respectively.     

Efficient green up-conversion emission in Yb3+/Ho3+ co-doped CaIn2O4

Intense green up-conversion (UC) emissions from ⁵F₄/⁵S₂ → ⁵I₈ transitions of Ho³⁺ in Yb³⁺/Ho³⁺ co-doped CaIn₂O₄ have been observed with excitation at 980 nm. The optimal processing parameters were determined by investigating emission intensities as a function of annealing temperature, duration time and Ho³⁺/Yb³⁺ dopant concentrations. It has been confirmed that the green UC luminescence was generated via a two-photon process from the quadratic dependence of the emission intensity on the pump power. A UC mechanism was proposed and the lifetime of the green emission was measured to be ～204 μs. The infrared-to-visible UC efficiency of the optimized CaIn₂O₄: 0.005Ho³⁺, 0.1Yb³⁺ sample increases to ～5.5% with the excitation power and saturates at 1.5 W. The chromaticity coordinates (0.281, 0.708) of the samples are located in the green region and hardly changed due to the negligible red emission. The results indicate that CaIn₂O₄: Yb³⁺, Ho³⁺ could act as an effective UC green light emitter and CaIn₂O₄ is an ideal oxide host for UC luminescence.     

Formation and characterization of mechanically alloyed Ti–Cu–Ni–Sn bulk metallic glass composites

In the present study, amorphous Ti₅₀Cu₂₈Ni₁₅Sn₇ and its composite powders reinforced with 4, 8, and 12 vol.% of W additions were prepared by mechanical alloying. After 5 h of milling, amorphous powders with homogeneously dispersed W nanoparticles were synthesized. The as-milled Ti₅₀Cu₂₈Ni₁₅Sn₇ and composite powders were then consolidated by vacuum hot pressing into disc compacts with a diameter and thickness of 4 and 10 mm, respectively.The structure of the as-milled powders and consolidated compacts was characterized by X-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy. While the thermal stability was examined by differential scanning calorimeter (DSC). In addition, the mechanical property of the consolidated BMGs was evaluated by Vickers microhardness tests. The experimental results showed that W nanoparticles ranged from 20 to 200 nm were embedded within the amorphous matrix. The presence of W nanoparticles did not dramatically change the glass formation ability of amorphous Ti₅₀Cu₂₈Ni₁₅Sn₇ powders. While the thermal stability of amorphous powders differed from those of its composites. A significant hardness increase with W additions was noticed for consolidated composite compacts.     

Interface reaction systematics in the Cu/In–48Sn/Cu system bonded by diffusion soldering

An alternative lead-free solder alloy In–48 at%Sn with a melting point of 120 °C and its implementation to bond Cu substrates in a diffusion soldering joining method are presented. According to the EPMA, TEM/EDX and electron diffraction analyses, two different behaviors were observed in the interconnection zone depending on the temperature range: (i) a single layer consisting of η phase below 200 °C; (ii) a Cu-poor region consisting of η phase and a Cu-rich layer formed by a mixture of thin alternate regions of ζ-Cu₁₀Sn₃ and δ-Cu₇In₃ phases perpendicular to the interconnection plane above 200 °C. The η layer shows two morphologies: large grains and fine grains at the η/In–48Sn (liquid) and at the η/Cu-rich interfaces, respectively. Additionally, the η region shows a gradual change in composition, suggesting a change from the Cu₆Sn₅ to the Cu₂In structures. Thermal stability tests indicate that the thermal resistance of the bonds is about 750 °C.     

First-principles investigation of the structural and electronic properties of Cu6−xNixSn5 (x = 0, 1, 2) intermetallic compounds

Cu_6−xNi_xSn₅ is an important intermetallic compound (IMC), which was known to greatly improve the reliability of the solder joints in integrated circuits. However, the improvement mechanisms and even the crystal structure of the IMC were not fully understood. In this paper, the first-principles calculations were performed to determine the stable structure of Cu_6−xNi_xSn₅ IMC. The structural and electronic properties of Cu_6−xNi_xSn₅ (x = 0, 1, 2) IMCs have been calculated. The results show that Ni atoms preferentially occupied 8f sites (Cu2) and formed Cu₄Ni₂Sn₅. The results of energy calculation and density of states demonstrate that this Cu₄Ni₂Sn₅ IMC had a more stable structure than Cu₆Sn₅. These results are also expected to account for the improvement in the reliability of the solder joint.     

Crystal structure and physical properties of a magnetic molecular conductor (EDO-TTFVODS)2FeCl4

Crystal structure, and electrical conducting and magnetic properties of a radical cation salt of EDO-TTFVODS with magnetic FeCl₄^? ion, (EDO-TTFVODS)₂FeCl₄ (EDO-TTFVODS = ethylenedioxytetrathiafulvalenoquinone-1,3-diselenolemethide) are reported. In this salt, there are two independent donor molecules formed two different layers A and B, and the counter FeCl₄^? ions layer is sandwiched between two donor layers A and B along the b-axis. The donor molecules form the one-dimensional columns along the a-axis in both donor layers. This salt shows high conductivity at room temperature (σ_RT = 25 S cm^?1) and a metallic behavior down to ca. 80 K, where a metal–insulator transition however occurs. The magnetic susceptibility obeys a Curie–Weiss law (Curie constant C = 4.42 emu K mol^?1 and Weiss temperature Θ = ?1.5 K), without any magnetic ordering down to 1.8 K. This result suggests the weak antiferromagnetic interaction between the d spins of FeCl₄^? ions.     

Thermal stability of the Pr3Pt4 compound

The temperature stability of the Pr₃Pt₄ compound was investigated by isothermal annealing at different temperatures, X-ray diffraction (XRD) and differential thermal analysis (DTA). It was found that the decomposition reaction Pr₃Pt₄ → PrPt + PrPt₂ took place at temperatures ranging approximately from 360 °C to 830 °C and it was an exothermal reaction. After annealing at 500–750 °C for 7 days, the Pr₃Pt₄ compound decomposes completely into the two neighboring compounds PrPt and PrPt₂.     

Ferroic transitions in the multiferroic (1 − x)Pb(Fe1/2Nb1/2)O3–xPbTiO3 system and its phase diagram

The results of the first comprehensive study of ferroic phase transitions as a function of temperature and compositions in the mixed multiferroic (1 ? x)Pb(Fe_1/2Nb_1/2)O₃–xPbTiO₃ (PFN–xPT) system are reported. Temperature-dependent powder synchrotron X-ray diffraction studies confirm unambiguously an interferroelectric transition between monoclinic and tetragonal phases for x ? 0.10. The tetragonal phase of PFN–xPT for x ? 0.10 and x > 0.10 is found to transform to the cubic phase on heating above room temperature. All these transitions are accompanied by distinct anomalies in the temperature dependence of dielectric constant. Our magnetization studies reveal that the nature of the magnetic phase transition changes across the morphotropic phase boundary (MPB) composition of PFN–xPT such that for tetragonal compositions with x > 0.08 there is only one magnetic transition, whereas two antiferromagnetic transitions are observed for monoclinic compositions with x < 0.08. These studies have enabled us to construct a phase diagram of PFN–xPT for the first time.