Ag Solid Solution Research Articles

Diffusional breakdown of nickel protective coatings on copper substrate in silver-copper eutectic melts

Diffusion couples with electrolessly plated nickel diffusion barriers between copper substrates and silver-copper eutectic alloys were tested at 800 °C and 850 °C, respectively. Growth of (Cu, Ni, Ag) ternary solid solution into the melt was observed at both temperatures. The growth pattern changed from cellular to dendritic as the temperature was increased from 800 °C to 850 °C. The nonplanar growth morphology can be explained in terms of constitutional supercooling in the melt. Kinetics of (Cu, Ni, Ag) solid solution growth were found to be controlled by interdiffusion at the interface of the nickel barrier and the growing solid-state phase. Local breakdown of the nickel diffusion barrier started once the (Cu, Ni, Ag) solid solution reached the copper substrate. Silver diffused from the silver-copper melt, through the ternary solid solution, dissolving copper and forming silver-copper liquid along copper grain boundaries. Ultimately, the nickel barrier was totally converted to the ternary solid solution, broke up, and floated into the liquid. Dissolution of the copper substrate occurred subsequently. A thin layer of chromium undercoating proved to be very effective in extending the protection time of the nickel diffusion barrier, due to the extremely low solubility of both copper and silver in chromium at these test temperatures.

Ar-ion irradiation of laser deposited FeAg thin films

Laser deposited FeAg alloys exhibit a supersaturation of the Fe(Ag) solid solution of up to 13 at.% Ag and an unusual lattice expansion in the growth direction. The relaxation process, grain coarsening, decomposition and mixing processes occurring during 350 keV Ar + irradiation at 77 K in these alloys were studied by X-ray diffraction. Depending on the original state of the samples, different processes dominate, but always lead to the same dynamic phase equilibrium under irradiation.

Magnetoresistance in Co-Ag multilayers and granular films produced by electrodeposition method

Giant magnetoresistance (GMR) in Co-Ag multilayers and granular films produced by electrodeposition have been investigated. The Co-Ag alloy films have an fcc structure for the full range of compositions and no Co and Ag solid solution is formed. The deposition current density influences the magnetoresistance of Co-Ag single layer films giving a maximum magnetoresistance of 5% for a Co/sub 32/Ag/sub 68/ alloy film deposited at a current density of 10 mA/cm/sup 2/, measured at room temperature and within a 21 kOe field. GMR has also been observed for Co-Ag multilayer films. Co/sub rich//Ag/sub rich/ multilayer films show magnetoresistance values of 8.7% at room temperature and within a 21 kOe magnetic field.

Effects of Small Amounts of Silver Added to NiGe Ohmic Contacts to n‐Type GaAs

The effects of a small amount of Ag addition to NiGe ohmic contacts on the electrical properties and the microstructure were investigated. The contact resistance of NiGe contacts was reduced by a factor of about three by adding a 6 nm thick Ag to the NiGe. This contact had a smooth surface, shallow reaction depth, a wide process window, and excellent thermal stability at 300°C after contact formation. The reduction of the contact resistances was believed to be due to formation of Ag(Ga) solid solutions, which facilitated heavy doping of Ge atoms into the Ga vacancies created at the GaAs surface. The present study suggests that the addition of a third element which has a wide solubility range with Ga is effective for the reduction of the resistances of the NiGe ohmic contacts.

Formation mechanism of a crystalline Ag50Pd50solid solution by impact ball–materials interaction

The formation of the crystalline Ag50Pd50 solid solution during mechanical alloying under shock interaction of Ag and Pd metallic powders has been studied using electron microscopy and X-ray diffraction. The process involved for impact interaction occurs via the incorporation of the small Pd particles into the Ag matrix in which, under the action of mechanical strain, the mutual diffusion of Ag and Pd leads to the formation of two solid solutions, one rich in Ag and the other rich in Pd. Further grinding allows the homogenization of the two Ag and Pd solid solutions whose composition changes to finally reach the initial Ag50Pd50 composition. The defects as dislocations generated by the impact conditions may be responsible for the reaction mechanism.

Effect of compaction pressure on the microstructure of mechanically alloyed Ag37Cu63alloy

Abstract A comparative study on mechanically alloyed Ag37CU63 alloy was carried out using TEM, XRD, DSC and fractography. The amorphous phase and supersaturated solid solution with the initial composition in the 1 GPa specimen transform into Cu-8 at.%Ag solid solution, Ag- and Cu-phases during heating. A higher compaction pressure accelerates this transformation. Since some of the mechanical alloying granules are composed from extremely small non-equilibrium grains, their melting point is about 150°C, which gives n different explanation of the DSC profiles.

Influence of 2D phase transitions on (111) surface segregation kinetics of Sn and Pb in Ge(Sn) and Ag(Pb) alloys

This paper deals with a comparative LEED-AES study of segregation of tin and lead on (111) surfaces from Ge(Sn) and Ag(Pb) solid solutions, respectively. The main feature of this work is the experimental observation of stepped kinetics in both cases even though the structures of the (111) surface in cubic diamond (Ge) and in fcc (Ag) lattices differ largely. This result is related to the occurrence and the stability of successive overlayers during the monolayer formation. Comparison with previous studies of the first stages of formation of ultra-thin layers of Sn and Pb onto Ge(111) and Ag(111) surfaces was carried out. The observed 2D phase transitions are explained by considering the energy of the different superficial sites which the segregated atoms can occupy.

Characterization of the defects responsible for the precipitation of silver from dilute PbAg solid solutions

The diffusion coefficients of silver ( D ∗ ) have been measured during its precipitation from dilute PbAg solid solutions (92 × 10 −6 at/at and 184 × 10 −6 at/at) by using 110Ag radiotracer between 327 and 363 K. The diffusion activation energy Q D ∗ = 49.4 kJ/mol is smaller than the diffusion activation energy ( Q D = 60kJ/mol) of silver in pure lead but is in fair agreement with the activation energy for precipitation of silver previously measured by the authors ( E a = 50 kJ/mol). Evidence that the (PbAg) pair is the defect responsible on the one hand for silver migration during the precipitation in these dilute alloys and on the other hand for silver diffusion in pure lead and lead-silver solid solutions is reviewed.

The effect of Ag diffusion on the crystal structure and electrical properties of Bi(Pb)SrCaCuO superconductors

X-ray diffraction of Bi(Pb)SrCaCuO compounds, prepared by a conventional solid-state technique, were measured from 20 degrees C to 500 degrees C. It was found that diffusion of Ag (600-825 degrees C) in Bi ceramics stimulates a high degree of grain orientation along the c-axis. In Ag-doped samples the lattice parameters a and c are decreased (in comparison with the undoped samples) and their dependences on temperature reveal a non-linear character. The critical temperature, determined from the resistivity measurements, for Ag-doped samples increased to 118 K. Ag diffusion at 790 degrees C increases the critical current density more than twice. The influence of low annealing temperature for Ag-doped samples on critical current density was also investigated. These results are discussed on the basis of precipitation of Ag solid solution in Bi(Pb)SrCaCuO superconductors.

The Ag-Bi (Silver-Bismuth) System

The solid solubility of Bi in (Ag) was estimated to be -3 at.% on the basis of X-ray work [31Bro]. Lattice parameter measurements of alloys at the temperature extremes of 200 and 259 ~ yielded solubilities of 0.312 and 0.784 at.% B i, respectively [40Chi]. More extensive studies of Bi solubility involving both micrographic and lattice parameter measurements between 266 and 900 ~ were conducted by [46Rau]. Bi solubility in (Ag) was studied by thermoelectric power and lattice parameter measurements over the temperature range 300 to 900 ~ [75Gla, 83Ako]. Recently, electron probe microanalysis (EPMA) of the Ag-rich phase quenched from 650 to 925 ~ in the two-phase region was reported [88Sch]. The solidus and solvus lines for the Ag side recommended in this evaluation are compared with all of the foregoing reported data in Fig. 3. The solidus line through the data points is based mainly on estimated thermodynamic data for the Ag solid solution. This is discussed in the "Thermodynamics" section. The projected solubility of Bi at 30 ~ is 0.004 at.%. On this basis, it appears that the solubility of 0.16 at.% reported by thermoelectric power measurement by [67Poi] at 30 ~ is excessive.

Formation and characterization of ohmic contacts to n–AlGaAs using Pd/AuGe/Ag/Au

Sequential deposition of Pd/AuGe/Ag/Au and rapid thermal annealing at 450 to 550 °C were employed to form a shallow ohmic contact to n–Alx Ga1−x As. Contact resistivity was in the range of (0.7–1) × 10−5 at x = 0.3 to (2–4) × 10−5 ohm-cm2 at x = 0.55. Limited interfacial reaction was verified by ion backscattering and x-ray diffraction techniques and attributed to the stability of Au–Ag solid solutions against underlying substrates. Contacts form at 450 to 500 °C, possibly via solid-state reaction, whereas liquid phase reaction may take place at 550 °C.

Local atomic environment in silver chlorobromides from exafs

The effect of variations in halide ratio on the local atomic environment of silver chlorobromides has been determined using EXAFS (extended X-ray absorption fine structure). The nearest-neighbor Ag-halide distances have been measured, at cryogenic temperatures, for Ag(Cl,Br) solid solutions ranging from pure AgCl to pure AgBr. Significant deviations of the EXAFS nearest-neighbor BrAg and AgCl distances from the “average” X-ray distance have been observed. The EXAFS nearest-neighbor distances are in agreement with the interatomic distance predicted by atomistic simulation studies and demonstrate the usefulness of combining theoretical and experimental methods in the study of the silver halides.

Localized Influence of Solute on the Stacking Fault Energy of Dilute Al-Based Solid Solutions

AbstractThe stacking fault energy (SFE) is widely used to classify the mechanical behavior of pure metals. In alloys, however, the experimentally observed SFE is strongly influenced by localized solute effects. To further understand these effects on dislocation structure and on the observed SFE, solute segregation to an extended edge dislocation dipole, delineating two stacking faults, was studied in dilute Al:Cu, Al:Ag, and Al:Cu, Ag solid solutions. Cu and Ag were chosen to isolate solute size and modulus effects, Cu being smaller than Al, while Ag and Al are essentially the same size. Atomistic Monte Carlo results showed little change in the partial dislocation spacing in the binary systems as compared to the spacing in pure Al, even though Cu was observed to segregate to the compressive regions of the dislocation dipoles, forming widespread atmospheres, while Ag formed randomly distributed Ag-rich zones. However, in ternary Al:Cu,Ag simulations, the Ag apparently inhibited the Cu from distributing across the width of the extended dislocations, both Ag and Cu forming small clusters near or on the partial dislocations which increased the partial dislocation spacing. Results will be discussed in light of interpretations of experimental SFE determinations, emphasizing the importance of the localized solute distribution on the SFE.

Equilibrium of segregation in Ag/Cu: influence of the orientation and temperature

We have used dissolution and segregation kinetics to investigate the equilibrium superficial segregation of silver on copper. The effect of surface orientation was deduced from dissolution kinetics at 450°C. A first-order phase transition occurs on a (111) surface; there is no evidence of such a transition on a (110) surface and, on a (100) surface, it is likely that a phase transition takes place at high coverage only. The effect of temperature was studied from segregation kinetics of silver on a (111)-oriented 0.45 at% Cu(Ag) solid solution at 450, 416 and 390°C. For θ < 0.6 the isotherms depicted a vertical part which was interpreted as a 2D phase transition; in this part a segregation enthalpy of about −100 kJ mol −1 was evaluated. For θ > 0.6 we found a slow-down in kinetics which is ascribed to the diminution of the relaxation energy with the silver superficial concentration.

Shallow ohmic contact formation by sequential deposition of Pd/AuGe/Ag/Au on GaAs and rapid thermal annealing

Shallow ohmic contacts to n-GaAs are fabricated by sequential deposition of Pd/AuGe/Ag/Au and rapid thermal annealing at 450–500 °C for 30 s. The metallization displays good electrical properties with a contact resistivity of 2 × 10−6 Ω cm2. The film–substrate reaction is extremely limited and the interface is uniform. A systematic study of various AuGe metallization schemes indicates that the limited interfacial reaction observed in the Pd/AuGe/Ag/Au structure correlates with the stability of Au–Ag solid solutions against GaAs. The diffusion of silver into the AuGe layer upon heating increases the eutectic temperature of the system. As a result, the contact stays in a solid state when the metallurgical reaction takes place to form an ohmic contact.

Method for calculating alloy energetics.

A semiempirical method for the computation of alloy energies is introduced. It is based on the equivalent-crystal theory of defect-formation energies in elemental solids. The method is both simple and accurate. Heats of formation as a function of composition are computed for some binary alloys of Cu, Ni, Al, Ag, Pd, Pt, and Au using the heats of solution in the dilute limit as experimental input. The separation of heats into strain and chemical components helps in understanding the energetics. In addition, lattice-parameter contractions seen in solid solutions of Ag and Au are accurately predicted. Good agreement with experiment is obtained in all cases.

Incomplete wetting of very dilute Cu(Ag) alloys by surface segregation

The equilibrium segregation isotherm derived from kinetics experiments on a dilute Cu(Ag) solid solution exhibits al T≅ 730 K a surface phase transition from almost pure Cu to almost pure Ag. The energetics of the driving forces being unambiguously defined from the electronic structure (TBIM: tight-binding Ising model), this transition can he easily interpreted in the framework of a simplified (Fowler-Guggenheim type) approach. A more sophisticated statistical treatment (APM: area preserving mapping) shows that this transition should be first of a finite succession of layering transitions leading to an incomplete Ag-wetting of the Cu(Ag) surface.

Incomplete wetting of very dilute Cu(Ag) alloys by surface segregation

The equilibrium segregation isotherm derived from kinetics experiments on a dilute Cu(Ag) solid solution exhibits al T≅ 730 K a surface phase transition from almost pure Cu to almost pure Ag. The energetics of the driving forces being unambiguously defined from the electronic structure (TBIM: tight-binding Ising model), this transition can he easily interpreted in the framework of a simplified (Fowler-Guggenheim type) approach. A more sophisticated statistical treatment (APM: area preserving mapping) shows that this transition should be first of a finite succession of layering transitions leading to an incomplete Ag-wetting of the Cu(Ag) surface.

Transport and thermal properties of the solid electrolyte Ag xCu 2-xHgI 4

Solid solutions Ag xCu 2-xHgI 4 prepared by a solution method were characterised by powder X-ray diffraction, differential scanning calorimetry (DSC) and electrical conductivity. X-ray diffractograms showed tetragonal phases over the whole range expept for 1.14 ⩽ × ⩽ 1.30 where a single cubic phase was seen. DSC showed a strong compositional dependence in the order-disorder transition temperature. Temperature variation of electrical conductivity carried out for all compositions showed an increase in conductivity by two orders of magnitude at the transition temperature. The composition x=1.14 having a maximum room temperature conductivity with a minimum transition temperature has the characteristics of an eutectoid of the Ag 2Hgl 4-Cu 2HgI 4 system.

高強度・高導電性Cu-Ag合金の開発

Development of highly conductive materials with high strength is requisite for conductors of high field magnets. To develop such materials, the Cu-Ag alloys (2-60 at%Ag) and their fabrication methods have been investigated. This paper describes the mechanical and electrical properties as well as the microstructure of the drawn wires of the alloys, as functions of Ag concentration and reduction in cross-sectional area (RA), and furthermore the heat-treatment effects on those properties.The Cu-Ag alloys were prepared by melting electrolytic Cu and pure Ag pellets in an argon atmosphere, and then cold-drawn to a 99.2%RA. The heat treatments were performed several times during the drawing process. The alloys consist of two phases, i. e. Cu solid solution (α-phase) and Ag solid solution (β-phase). These two phases can be drawn down to fine fibers below μm in diameter. The relationship between the tensile strength and the fiber diameter follows the Hall-Petch formula. The optimum combination of the high strength and the high electrical conductivity were obtained, by cold-drawing the alloy with intermediate heat treatments at 350-450°C for 1-2 h. On the other hand, heat treatments prior to the drawing process scarcely influence on those properties. The heat-treated Cu-16 at%Ag composite of 99%RA showed the ultimate tensile strength of 1000 MPa and the electrical conductivity of 80%IACS, at room temperature.Since the Cu-Ag alloys fabricated by the present method have higher values of both tensile strength and conductivity than those of Cu-Nb and other Cu-based alloys, they would become the most promising conductor materials for the high field magnets.