Increasing Silver Content Research Articles

An evidence for a microscopic phase separation in AsSeAg glasses revealed by thermal and structural investigations

Alternating Differential Scanning Calorimetric (ADSC) studies show that Se rich As20Se80-xAgx (0 ≤ x ≤ 15) glasses exhibit two endothermic glass transitions and two exothermic crystallization peaks; the observed thermal behavior has been understood on the basis that As20Se80-xAgx glasses are microscopically phase separated, containing Ag2Se phases embedded in an As-Se backbone. With increasing silver concentration, the Ag2Se phase percolates in the As-Se matrix, with a well-defined percolation threshold at x = 8. A signature of this percolation transition is shown up in the thermal behavior, as sudden jumps in the composition dependence of non-reversing enthalpy, ΔHnr obtained at the second glass transition reaction. Scanning Electron Microscopic (SEM) studies also confirm the microscopic phase separation in these glasses. The super-ionic conduction observed earlier in these glasses at higher silver proportions, is likely to be associated with the silver phase percolation.

Impact of Silver Addition on Room Temperature Magneto-Resistance in La0.7Ba0.3MnO3 (LBMO): Ag x (x=0.0, 0.1, 0.2, 0.3, 0.4)

La0.7Ba0.3MnO3 (LBMO): Ag x (x=0.0, 0.1, 0.2, 0.3, and 0.4) composites are synthesized by a solid-state reaction route, the final sintering temperatures are varied from 1300 °C (LBMO1300Ag) to 1400 °C (LBMO1400Ag), and their physical properties are compared as a function of temperature and Ag content. All samples are crystallized in single phase accompanied by some distortion in main structural phase peaks at higher angles with an increase in silver content. Though the lattice parameters (a,c) decrease, the b increases slightly with an increase in Ag content. The scanning electron micrographs (SEM) showed better grains morphology in terms of size and diffusion of grain boundaries with an increase in Ag content. In both LBMO1300Ag and LBMO1400Ag series, the metal insulator transition (T MI) and accompanied paramagnetic-ferromagnetic transition (T C) temperatures are decreased with an increase in Ag content. The sharpness of MI transition, defined by temperature coefficient of resistance (TCR), is improved for Ag added samples. At a particular content of Ag(0.3), the T MI and T C are tuned to 300 K and maximum magneto-resistance at 7 Tesla applied field (MR7 T) of up to 55% is achieved at this temperature, which is more than double to that as observed for pure samples of the both 1300 and 1400 °C series at same temperature. The MR7 T is further increased to above 60% for LBMOAg(0.4) samples, but is at 270 K. The MR7 T is measured at varying temperatures of 5, 100, 200, 300, and 400 K in varying fields from ±7 Tesla, which exhibits U and V type shapes. Summarily, the addition of Ag in LBMO improves significantly the morphology of the grains and results in better physical properties of the parent manganite system.

Electrical conductivity of silver bismuth borate tellurite glasses

The AC electrical conductivity of (Ag 2O) x (Bi 2O 3) 30 (B 2O 3) 60− x (TeO 2) 10 glass ( x=0, 2, 4, 5, 10, 15 and 20) were measured at different temperatures and frequencies. The results obtained indicated that glasses containing silver<5 mol% have values nearly approximately equal to AC electrical conductivity. A slight decrease was observed with increasing Ag 2O concentration up to 4 mol%. However, the AC electrical conductivity values increase with increasing silver content, i.e. ⩾5 mol%. The AC electrical conductivity values, increased with increasing frequency and follow the power law, σ AC= Aω s . The frequency exponent s was found to be dependent on frequency and temperature. The s values tended to increase to unity as the temperature decreased. Such results suggest that the correlated barrier-hopping (CBH) model is appropriate for explaining the AC electrical conductivity in these glasses. A pronounced increase in the dielectric loss values was observed with increasing silver content. These reflect the effect of Ag + ions charge carriers on the electrical conductivity of such glasses.

Binding energy and preferred adsorption sites of CO on gold and silver–gold cluster cations: Adsorption kinetics and quantum chemical calculations

We revisit the reactivity of trapped pure gold (Au(n)+, n < 26) and silver gold alloy cluster cations (Ag(m)Au(n)+, m + n < 7) with carbon monoxide as studied in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. The experimental results are discussed in terms of ab initio computations which provide a comprehensive picture of the chemical binding behaviour (like binding energy, adsorption sites, associated vibrational frequencies) of CO to the noble metal as a function of cluster size and composition. Starting from results for pure gold cluster cations for which an overall decrease of CO binding energy with increasing cluster size was experimentally observed--from about 1.09 +/- 0.1 eV (for n = 6) to below 0.65 +/- 0.1 eV (for n > 26) we demonstrate that metal--CO bond energies correlate with the total electron density and with the energy of the lowest unoccupied molecular orbital (LUMO) on the bare metal cluster cation as obtained by density functional theory (DFT) computations. This is a consequence of the predominantly sigma-donating character of the CO-M bond. Further support for this concept is found by contrasting the predictions of binding energies to the experimental results for small alloy cluster cations (Ag(m)Au(n)+, 4 < m + n < 7) as a function of composition. Here, binding energy drops with increasing silver content, while CO still binds always in a head-on fashion to a gold atom. Finally we show how the CO stretch frequency of Ag(m)Au(n)CO+ may be used to identify possible adsorption sites and pre-screen favorable isomers.

Nanostructure, interactions, and conductivities of polymer electrolytes comprising silver salt and microphase‐separated graft copolymer

AbstractSilver polymer electrolytes were prepared by blending silver salt with poly(oxyethylene)9 methacrylate)‐graft‐poly(dimethyl siloxane), POEM‐g‐PDMS, confining silver salts within the continuous ion‐conducting POEM domains of microphase‐separated graft copolymer. AgClO4 polymer electrolytes exhibited their maximum conductivity at high silver concentrations as well as higher ionic conductivities than AgCF3SO3 electrolytes. The difference in conductivities of the two electrolytes was investigated in terms of the differences in the interactions of silver ions with ether oxygen of POEM and, hence, with the anions of salts. Upon the addition of salt in graft copolymer, the increase of Tg in AgClO4 was higher than that in AgCF3SO3 electrolytes. Analysis of an extended configuration entropy model revealed that the interaction of ether oxygen/AgClO4 was stronger than that of ether oxygen/AgCF3SO3 whereas the interaction of Ag+/ClO4− was weaker than that of Ag+/CF3SO3−. These interactions are supported by the anion vibration mode of FT‐Raman spectroscopy. It is thus concluded that the higher ionic conductivity of AgClO4 electrolytes was mostly because of higher concentrations of free ions, resulting from their strong ether oxygen/silver ion and weak silver ion/anion interactions. A small angle X‐ray scattering study also showed that the connectivity of the POEM phase was well developed to form nanophase morphology and the domain periodicities of graft copolymer electrolytes monotonically increased with the increase of silver concentration up to critical concentrations, after which the connectivity was less developed and the domain spacings remained invariant. This is attributed to the fact that silver salts are spatially and selectively incorporated in conducting POEM domains as free ions up to critical concentrations, after which they are distributed in both domains as ion pairs without selectivity. The increase of domain d‐spacing in AgClO4 electrolytes was larger than that in AgCF3SO3, which again results from high concentrations of free ions in the former. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1018–1025, 2007

Behavior of ultra fine silver-BaTiO3 composite powders at sintering

In this paper, the metal–ceramic composite material, i.e., silver–BaTiO3 composite powder, was prepared with chemical deposition method. Composition, dispersibility and shape of powder particles were investigated by XRD, SEM and size distribution analyzer. Coalescence of particles occurs during low sintering process, and sintering temperature has a great effect on composition and shape of single powder particles. The sintering of silver on the surface of particles increases with an increasing temperature by SEM and EDX observation. The shrinkage and softening temperature of composite powders increase and decrease as an increasing silver content, respectively, by TMA analysis. Sheet resistance 52 mΩ/□ was observed from the film corresponding to 80 wt.% silver content which was sintered at 300 °C.

Fabrication and Evaluation of PZT/Ag Piezoelectric Composites and Graded Actuator

Homogeneous PZT/Ag composites and compositionally graded PZT/Ag actuators were fabricated and evaluated in this work. The piezoelectric constant decreases gradually and the dielectric constant increases significantly with an increase in silver content of the PZT/Ag composites. The fracture toughness of the PZT/Ag composites is enhanced with addition of the silver powders. Based on the corresponding piezoelectric properties of the monolithic PZT/Ag composites, a graded material with symmetric silver compositions from 1 to 10 vol % then inversely to 1 vol % was successfully fabricated by conventional sintering. This study indicates that the PZT/Ag composites can be used to acting as bimorph actuator materials.

Reactions of mixed silver-gold cluster cations AgmAun+ (m+n=4,5,6) with CO: Radiative association kinetics and density functional theory computations

Near thermal energy reactive collisions of small mixed metal cluster cations Ag(m)Au(n) (+) (m+n=4, 5, and 6) with carbon monoxide have been studied in the room temperature Penning trap of a Fourier transform ion-cyclotron-resonance mass spectrometer as a function of cluster size and composition. The tetrameric species AgAu(3) (+) and Ag(2)Au(2) (+) are found to react dissociatively by way of Au or Ag atom loss, respectively, to form the cluster carbonyl AgAu(2)CO(+). In contrast, measurements on a selection of pentamers and hexamers show that CO is added with absolute rate constants that decrease with increasing silver content. Experimentally determined absolute rate constants for CO adsorption were analyzed using the radiative association kinetics model to obtain cluster cation-CO binding energies ranging from 0.77 to 1.09 eV. High-level ab initio density functional theory (DFT) computations identifying the lowest-energy cluster isomers and the respective CO adsorption energies are in good agreement with the experimental findings clearly showing that CO binds in a "head-on" fashion to a gold atom in the mixed clusters. DFT exploration of reaction pathways in the case of Ag(2)Au(2) (+) suggests that exoergicities are high enough to access the minimum energy products for all reactive clusters probed.

Hydrogen permeability study of the thin Pd–Ag alloy membranes in the temperature range across the α–β phase transition

A series of Pd–Ag membranes with different atomic ratio (Ag = 0, 5, 10, 15, 20 and 23%) was fabricated by controlling the chemical components in the electroless plating bath followed by thermal annealing of the deposited metals. Gas permeation of the membranes was examined at the temperature ranges at 100–300 °C. The hydrogen flux for the membranes of low Ag content gave a marked change giving a peak in the range of 170–200 °C, which was attributed to the α–β crystal phase transition of the hydride. The peak in hydrogen flux became less significant and appears as shoulder along with the increase of silver content. This observation coincides with the decrease of lattice size difference between α and β phase by the increase of Ag content in the Pd–Ag alloy. Improved durability of the alloy membrane (Ag > 20%) was demonstrated by cyclic change of gas and temperature and was attributed to the suppression of lattice expansion by alloying with more than 20% of silver.

Optical properties and structure of amorphous films Agx(As0.33S0.67−ySey)100−x

As33S67−ySey, where y=0, 16.75, 33.5, 50.25 and 67, amorphous thin films were prepared by a vacuum thermal evaporation technique. The films with known silver concentrations and good optical quality were prepared by thermal vacuum evaporation of a silver film on the top of As33S100−ySey films with sequential step-by-step optically- and thermally-induced diffusion and dissolution (OIDD) of silver. The range of silver content was x=0–25at.%. The kinetics of OIDD of silver were measured optically by monitoring the change of thickness of the undoped part of the chalcogenide during broadband illumination. Compositions of the reaction products have been determined by scanning electron microscope with energy-dispersive X-ray microanalyser EDS. Optical properties (T,n,Egopt) of thin films were measured and/or calculated by the Swanepoel method [R. Swanepoel, J. Phys. E: Sci. Instrum. 16 (1983) 1214]. The refractive index increase with increasing silver and selenium concentration has been shown. The difference of the refractive index (Δn) between undoped and silver doped films was ∼0.4 and between As33S67 and As33Se67 was films ∼0.42. Non-linear indices of refraction were estimated according to Tichy’s formula [H. Ticha, L. Tichy, J. Optoel, Adv. Mat. 4 (2002) 381]. The values of non-linear refractive index grew with increasing silver and selenium content. The difference of optical bandgap, ΔEgopt, between undoped As33S67 and fully doped films with Ag and Se was ∼1eV. Raman spectroscopy showed a decrease in S–S or Se–Se bonds with increasing silver content.

Characterisation of barium titanate-silver composites, part I: Microstructure and mechanical properties

The paper presents an investigation of the influence of silver particles on the microstructure and mechanical properties of barium titanate. Barium titanate-silver composites have been prepared by ball milling precursor powder constituents; followed by drying, sieving and calcination prior to powder compaction. After sintering the green compacts, microstructural analysis was undertaken involving measurement of grain size, silver particle size, phase composition and phase content. Characterisation of mechanical strength, toughness, hardness and stiffness was also undertaken. Reaction product phases between silver and barium titanate could not be detected. The dispersed silver particles were shown to inhibit densification. Silver particles below 1 μm in size were intragranular and attached to domains. The size of the intergranular silver particles increased with silver content. An increase in silver content improved whereas strength, hardness and stiffness decreased, while toughness was unchanged.

Dielectric behavior of lead zirconate titanate/silver composites

Dielectric properties of PZT/Ag composites have been investigated. The dielectric constant of PZT/Ag composite increases significantly with increasing silver content, whereas, dissipation factor increases little. The dielectric constant of PZT/Ag composite with 8 vol.% Ag is above six times higher than that of the monolithic PZT. The dielectric peak temperatures are slightly shifted to low temperatures with the silver addition. The dielectric constants of PZT/Ag composites are frequency dependent in the case of the high Ag content (>1 vol.%).

Properties of titanium–silver alloys for dental application

The purpose of this study was to develop titanium-silver alloys with biocompatibility, high corrosion resistance, and low ion-release rate, and to evaluate the electrochemical properties of titanium-silver alloys in artificial saliva. Titanium-silver alloys with silver contents ranging from 0 to 4.5 at % in steps of 0.5 at % were designed. The alloys were arc melted, homogenized at 950 degrees C for 72 h, hot rolled to 2 mm in thickness, and finally solution heat treated at 950 degrees C for 1 h and quenched in water. Chemical compositions, phases, hardnesses, electrochemical properties, and the cytotoxicity of the alloys were investigated. The purity of titanium-silver alloys was maintained above 99.9%, because few impurities were introduced through their manufacture. In the case of alloys containing silver in the range 2.0-4.0 at %, the formation of an acicular alpha phase was observed inside the beta phase. The acicular phase got thinner with increasing amounts of silver. This means that silver is a beta-phase stabilizing element in titanium-silver alloys. The hardness value tended to rise with increasing silver content and increased largely over 3.5 at %, and the increase of the hardness value versus pure titanium was about 33%. It is believed that the substantial increases in hardness was due to the effects of solid solution strengthening and of alpha-beta phase transition. Moreover, titanium-silver alloys had higher corrosion resistances than pure titanium. These results mean that silver additions to titanium can improve alloy corrosion resistance. Passive current densities in the potentiodynamic polarization curves were dependent on the chemical compositions of the titanium-silver alloys. However, they did not show a linear relationship with respect to silver contents. Titanium-silver alloys did not show pitting corrosion in artificial saliva. It is believed that silver addition to titanium strengthened the passive film due to titanium dissolution induced by the different electromotive forces of titanium and silver. In the agar overlay test, the cytotoxicity of the titanium-silver alloys and of titanium were none or mild. In summary, titanium-silver alloys had higher mechanical properties and corrosion resistance than titanium, and toxicities that were similar to titanium. Therefore, it is recommended that titanium-silver alloys be adopted cautiously by the biomedical and dental fields.

Adsorptive removal of dimethylsulfide and t-butylmercaptan from pipeline natural gas fuel on Ag zeolites under ambient conditions

Desulfurization of pipeline natural gas fuel at ambient conditions before introduction to reforming processes is strongly needed for stationary applications of fuel cells. Adsorptive removal of dimethlysulfide (DMS) and t-butylmercaptan (TBM) from pipeline natural gas was efficiently carried out by using silver exchanged Y zeolites (AgNa-Y) in the presence of water at room temperature and normal pressure. The capacity and adsorptivity for DMS and TBM on AgNa-Y were improved by an increase in silver content of AgNa-Y. Adsorption runs for DMS and TBM were carried out separately to compare their adsorptivity on AgNa-Y. The sulfur adsorption capacity for DMS on Ag(18)Na-Y (1.9mmolg−1) was much higher than that for TBM (0.6mmolg−1). The clear color change of AgNa-Y during the period of adsorption run provides information regarding the formation of silver sulfide species on AgNa-Y. The used AgNa-Y was regenerated easily by heat treatment in air at 500°C.

Signature of a silver phase percolation threshold in microscopically phase separated ternary Ge0.15Se0.85−xAgx (⩽x⩽0.20) glasses

Temperature modulated alternating differential scanning calorimetric studies show that Se rich Ge0.15Se0.85−xAgx (0⩽x⩽0.20) glasses are microscopically phase separated, containing Ag2Se phases embedded in a Ge0.15Se0.85 backbone. With increasing silver concentration, Ag2Se phase percolates in the Ge–Se matrix, with a well-defined percolation threshold at x=0.10. A signature of this percolation transition is shown up in the thermal behavior, as the appearance of two exothermic crystallization peaks. Density, molar volume, and microhardness measurements, undertaken in the present study, also strongly support this view of percolation transition. The superionic conduction observed earlier in these glasses at higher silver proportions is likely to be connected with the silver phase percolation.

Solid solutions La 1− xAg yMnO 3+ δ: evidence for silver doping, structure and properties

Our experiments on the preparation of the composites of CMR manganites and metal silver have shown that in the case of La 1− x MnO 3+ δ the vacancies in the A-sublattice of the perovskite structure can be filled by Ag + ions under the soft conditions of the synthesis. Neutron diffraction refinement of La 0.8Ag 0.2MnO 3.00 clearly proves the silver doping in the A-sublattice. Depending on P(O 2)– T synthesis conditions the solid solutions with the broad stoichiometry range La 1− x Ag y MnO 3+ δ (0.3 ≥ x ≥ y) were prepared. We report here the evolution of the oxygen stoichiometry, the crystal structure as well as electro-physical properties in the series of the solid solutions. Curie temperature comes over a maximum exceeding the room temperature with the increase of silver content. La 1− x Ag y MnO 3+ δ solid solutions can be useful for the construction of the room temperature magnetic field sensors based on the magnetoresistance effect.

Ionic conductivity (Ag +) in AgGeSe glasses

Ag x (Ge 0.25Se 0.75) 100− x (10≤ x≤25 at.%) ionic conductor glasses, prepared by a melt-quenching method, are investigated by impedance spectroscopy in the frequency range 5 Hz–2 MHz at different temperatures T from room temperature to 363 K. The conductivity of the glasses σ was obtained as a function of the silver concentration and the temperature. The temperature dependence of the ionic conductivity follows an Arrhenius type equation σ=( σ 0/ T)·exp(− E σ / kT). The activation energy of the ionic conductivity E σ and the preexponential term σ 0 were calculated. It was found that the room temperature conductivity increases by a factor of about 10 with increasing silver content (1.32 10 −5 S cm −1 at x=10 and 1.09 10 −4 S cm −1 at x=25), while the activation energy decreases from 0.367 to 0.339 eV. The diffusion coefficient of the Ag + ions was estimated. In addition, a model proposed by Elliott was applied to determine the activation energy of conductivity in the high-modifier-content region. The results are discussed in connection with structural aspects and with those published in the literature related to other chalcogenide and chalcohalide systems.

Effect of silver co-sputtering on amorphous V2O5 thin-films for microbatteries

Abstract The effect of silver co-sputtering on the microstructural and electrical properties of amorphous V2O5 films is investigated. The films are grown by dc reactive sputtering and are applicable to thin-film microbattery cathodes. Analysis with glancing-angle X-ray diffraction (GXRD), scanning electron microscopy (SEM), X-ray photon spectroscopy (XPS), and Fourier transformation infrared (FT-IR) spectroscopy confirm that the growing rate, silver content and microsturucture of the V2O5 films are dominantly affected by the r.f. power supplied on the silver metal targets. The discharge capacity and cycle ability of microbatteries increases with increasing silver content in the thin cathode films. In addition, it is found that silver co-sputtered V2O5 cathode films, if only obtained at not more than 30 W, exhibit better discharge capacity, cycle ability and lithium-ion diffusivity than an undoped V2O5 cathode film. This is due to increases both in the electronic conductivity with doping elements of high electronic conductivity and in the distance between two adjacent V2O5 layers by co-sputtered silver atoms.

Characterization of polyimide irradiated in silver solution with a pulsed electron beam

Polyimide samples (50 μm × 12 mm × 12 mm) were immersed in AgNO 3 solution and exposed to a pulsed beam of 6-MeV electrons, with pulse width ∼1.6 μs and repetition rate 50 pps. The exposure time was changed from 20 and 50 min. Over this period the electron fluence received by the polyimide samples varied in the range of 2 × 10 15–5 × 10 15 e/cm 2. The presence of silver in the polyimide sample was confirmed by the XRF technique. The relative concentration of silver in these polyimide samples was found to increase with increasing irradiation time. These irradiated polyimide samples were also characterized by the RBS technique. The results showed the diffusion of silver in the polyimide samples to a depth of 2.5 μm, at room temperature. The measured value of the diffusion coefficient, D ′, of silver in the polyimide varied from 1.26 × 10 −13 to 9.3 × 10 −14 m 2/s over a range of electron fluence 2 × 10 15–5 × 10 15 e/cm 2. This value of the diffusion coefficient, D ′, is around six orders of magnitude higher than that of the thermal diffusion coefficient, D, of silver in polyimide at ∼300 °C. Clustering of the silver atoms and bridging between the silver atoms and the polyimide segments may be the causes for the observed decrease in the diffusion coefficient, D ′, at higher electron fluences. In addition, the polyimide samples were characterized by dielectric relaxation spectroscopy. The dielectric constant, ε ′, of the polyimide samples was found to increase with increasing silver concentration and reached a value of 4.12, as compared to 3.15 of the virgin polyimide, measured at 1 kHz. The increase in the dielectric constant, ε ′, is, however, not commensurate with the number of silver atoms diffused in the polyimide, as per the Clausis–Mossotti equation. This indicates that the free volume produced in the polyimide by electrons acts in the opposite direction to that of the silver atoms which enhance the dielectric constant, ε ′, through dipolar interactions with the carbonyl group of the polyimide. The diffusion of an appreciable amount of silver into polyimide at room temperature in a period of 0.3 s is an unique example of the radiation-enhanced diffusion of silver in polyimide by employing pulsed electron beams.

Effect of silver content on the shear fatigue properties of Sn-Ag-Cu flip-chip interconnects

The mechanical shear fatigue test has been performed to study the effect of silver content on the fatigue properties of Sn-xAg-0.5Cu (x=1, 2, 3, and 4) for flip-chip interconnections. The strength of the solder alloy increases with increasing silver content, preventing shear plastic deformation of the solder bump. The flip-chip joints made using higher silver content solder, such as 3%Ag and 4%Ag, exhibit longer fatigue life for all conditions. The fatigue ductility of the solder decreases with an increase in the silver content. The fatigue endurance of 1%Ag solder is superior to other solders over the plastic strain range of 3%, even though the strength of the solder is the lowest in the solders tested. Based on this study, the 3Ag solder may exhibit good fatigue performance for all conditions, and the 1Ag solder is optimum for severe strain conditions.