Electromigration of copper in lead

The electromigration of copper in lead was measured under isothermal conditions by a steady-state method. ⁶⁴Cu was introduced into the lead solvent as a radioactive tracer solute. After electromigration, the steady-state, concentration-distance curve was determined by standard sectioning, weighing and counting techniques. Although the experiments extend from 215 to 303°C, the measurements for Z¹, the effective charge number for copper in lead, appear to show at low temperature a strong dependence on concentration and are also difficult to reproduce satisfactorily in this temperature range. Accordingly only the results in the range from 240°C and up have been included in calculating the electromigration parameters. These results give Z¹ in the range 1.1 ± 0.3 and indicate an electrostatic charge, Z_el, of 1,8 ±0.9.     

Ion exchange properties of lithium iron oxides

The αLiFeO₂ rock salt material has been prepared from lithium carbonate and ferric oxide. It was found that the lithium can be exchanged for silver in silver nitrate and, initially, a substituted rock salt is produced, Ag_xLi_1−xFeO₂. The ultimate phase in the ion-exchange process is αAgFeO₂. The diffusion coefficient of Ag in Ag_xLiFeO₂, determined by transient electrochemical measurements, was found to be around 5 × 10⁻⁸ cm⁻² s⁻¹.     

Variations of Ag bonding distances in the AgBr1−xIx solid-solution with rock-salt type structure by X-ray and EXAFS analyses

The local structure of the AgBr_1−xI_x rock-salt type solid-solution (0≤×≤0.4) was investigated by both EXAFS and single crystal X-ray diffraction. The first nearest neighbor distances from Br to Ag, and those from Ag to Br in the solid-solution can be determined from EXAFS method. Because Ag⁺ surrounded by both Br⁻ and I⁻ ions is locally attracted to Br⁻, which has larger effective negative charge than I⁻, the Ag-Br distances gradually decrease with AgI content. There are observed systematic changes in both Br K- and Ag K-edge XANES spectra with increasing AgI content in connection with the change of the local structure in the solid-solution. The Br and I ions are distributed at random over the 4(a) sites of space group Fm3m without forming clusters. Both cation and anion are displaced from the lattice site because the Ag-Br and Ag-I distances in the solid-solution are close, respectively, to the distances in the pure rock-salt type AgBr and a hypothetical rock-salt type AgI. The particular increase in temperature factors by X-ray diffraction results from the static displacements of both cations and anions from the normal octahedral site. A large enhancement of ionic conductivity in AgI rich region will be ascribed to an increase in the concentration of the Frenkel defect caused by changes in local structures in an equilibrium state.     

Comparison between the magnetic susceptibilities of Pd1−xAgx and single phase PdHn

The rapid decrease of the isothermal magnetic susceptibility χ of single phase PdH_n with n ( = atomic ratio H/Pd) above the critical temperature T_c = 564 differs from that of the magnetically similar single phase system Pd_1−xAg_x (x: silver mole fraction) at the same temperature and at equal valence electron concentrations (n = x), i.e. χ (PdH_n)−χ(Pd_1−xAg_x) <0. By use of a semiphenomenological susceptibility ansatz related to the nonideal solution behaviour of H (Ag) in Pd the susceptibility difference is interpreted as an electronic excess effect.The analysis of the steep descent of the magnetic susceptibility also applies to the Pd-rich side of PdH_n in the subcritical temperature region (so-called α-phase) and can be supported by ¹⁰⁵Pd Knight shift data at 348 K.     

A molecular dynamics investigation of the micro-mechanism for vacancy formation between Ag3Sn and βSn under electromigration

In this paper, the vacancy formation at the interface between different grains (Ag₃Sn and βSn) induced by electromigration was investigated from the perspective of atom diffusion. To explain the micro-mechanism of void formation near the interface, the diffusion coefficient was specifically studied here via molecular dynamics (MD) simulation. By comparing the atom diffusion rates of atoms in βSn and Ag₃Sn, a significant difference could be observed when the temperature is up to 400 K. The Sn atoms in βSn have a higher diffusion coefficient (8E ? 9 cm²/s) than atoms in Ag₃Sn (4E ? 9 cm²/s), which indicated that the void would be prone to appear in βSn near the interface. Moreover, the effect of grain size and pressure on atom diffusivity was studied. Results show that the atom diffusivity depends heavily on the grain size of Ag₃Sn. When the thickness of Ag₃Sn is increased from 4 to 12 nm, this difference is significant when the temperature is only 375 K. On the other hand, the atom diffusion character of Ag₃Sn and βSn changes substantially under constant pressure. The difference of the atom diffusion rate would be inhibited by pressure perpendicular to the interface, which indicated voids have less possibility to appear herein.     

Mixed cationic effect in the Li/AgB2O3P2O5 glasses

Electrical conductivity data have been determined for a series of x Ag₂O(1 − x)Li₂OB₂O₃P₂O₅ glasses. The progressive substitution of Li⁺ by Ag⁺ considerably decreases the ionic conductivity which shows a minimum at Ag/(Ag + Li) = 0.4. This behaviour becomes intense as the temperature is lowered. This mixed cationic effect is further characterised by activation energy and conductivity relaxation time going to a maxima where conductivity minima occurs. ac conductivity and electric modulus response of those glasses are discussed.     

Electromigration in polycrystalline and single crystal magnesium

The electromigration of magnesium single and polycrystal samples was measured under the influence of a d.c. current density of approximately $\text{6×10}{}^3\text{A}\text{cm}{}^2$ using the vacancy flux technique. The single crystal data were taken on samples with the c-axis of the metal making angles of 22° and 63° respectively with the cylindrical axis of the specimen. Accurate measurements of the longitudinal and transverse motion were made over a period of several weeks and used to calculate a value for the atom drift velocity, V_a. The atom drift velocity is used to calculate Z¹, the effective eiectromigration charge on the ion. All of the observed motion was directed toward the anode. The polycrystal runs yielded an average value of $\text{Z}{}^1\text{?}\text{= ?2.03 ±0.33}$. The single crystal runs resulted in an anisotropic drift velocity ratio of $\text{V}{}_{\mathrm{a\perp }}\text{V}{}_{\mathrm{a\parallel }}\text{= 1.4}$. However, the product of diffusivity times resistivity is anisotropic by the same ratio as the atom drift velocity and the correlation factor f is nearly isotropic for magnesium. As a result Z¹ is isotropic and turns out to be ?1.6.     

Etude comparative des structures des alumines β stoechiometrique et non stoechiometrique: Etude par diffraction des rayons X (I)

The average structures of non-stoichiometric β_AgNS 11 Al₂O₃-1.25(Ag₂O) and stoichiometricβ_AgS 11 Al₂O₃-0.95 Ag₂O β alumina are determined by X-ray diffraction techniques (R factors 4 and 5% respectively). In both compounds Ag⁺ ions are localized on two off-centers Beevers-Ross positions (BRD) very close to one another and with almost equal occupation factors. The evolution from β_AgNS to /gbS occurs through the decrease of the occupation factor of the anti-Beevers-Ross site and the disappearance of the Frenkel defect. A long range ordered superstructure in β_AgS with the lattice constants a√(3)?a√(3)?c (P6₃/m is observed at room temperature and found to arise from the in layer Ag and O ions. The BRD and Oxygen (5) ions are ordered on off-centered positions around an empty aBR site. The complementary structure reflections are interpreted in a twinned model with two types of domains, for the in layer ions.     

The anomalous quasi isotropic [g] tensor found for CdBr2:Ag2+ and AgBr0.15Cl0.85:Ag2+: An explanation through strong covalency

The “anomalous” quasi-isotropic [g] tensor observed in systems containing the elongated AgBr⁴⁻₆ unit (g_∥ = 2.078 ± 0.003; g⊥ = 2.065 ± 0.003) is reasonably explained, within a rigorous Molecular Orbital framework, in terms of a very high covalency, consistent with the optical electronegativity of Ag²⁺ and previous results on other Cu²⁺ and Ag²⁺ complexes. For the antibonding level 3b_1g(x² − y²) about 90% of the electronic charges should be on bromine ions. The present analysis reveals that g_∥ − g₀ is dominated by charge-transfer excitations while g_⊥− g₀ is dominated by crystal-field excitations.     

NQR, NMR and Crystal Structure Studies of [C(NH2)3]2HgX4 (X = Br, I)

The crystal structure of [C(NH₂)₃]₂HgBr₄ has been determined at room temperature: monoclinic, space group C2/c, with a = 10.035(2), b = 11.164(2), c = 13.358(3) Å, β = 111.67(3)°, and Z = 4. The crystal consists of planar [C(NH₂)₃]⁺ and distorted tetrahedral [HgBr₄]^2? ions. The Hg atom is located on a two-fold axis such that two sets of inequivalent Br atoms exist in an [HgBr₄]^2? ion. In accordance with the crystal structure, two ⁸¹Br NQR lines widely separated in frequency were observed between 77 and ca. 380 K. [C(NH₂)₃]₂HgI₄ yielded four ¹²⁷I NQR lines ascribable to m = ±1/2 ? ±3/2 transitions, indicating that its crystal structure is different from the bromide complex. The ¹H NMR T ₁ measurements showed a single minimum for the bromide but two minima for the iodide. The analyses based on the C₃ reorientations of the planar [C(NH₂)₃]⁺ ions gave the activation energies of 29.8 kJ mol^?1 for the bromide, and 30.2 and 40.0 kJ mol^?1 for the iodide.     

Mössbauer studies of microscopic disorder in solid electrolytes

We implement for the first time Mössbauer Spectroscopy (MS) to investigate short-range properties of disorder in solid electrolytes. MS in¹²⁹I and¹¹⁹Sn was carried out in RbAg₄I₅ and as impurity in Ag₂Se, respectively. Measurements were performed both in the superionic and the normal phases. It is shown that localized cation hopping is an inherent feature of the α-AgI-type solid electrolytes. In RbAg₄I₅, at temperatures far belowT _c, a small fraction of Ag is still locally mobile and atT>T _c, its concentration increases exponentially. A strong linear temperature dependence of the point-charge electric field gradient is observed and explained in terms of local hopping. With¹¹⁹Sn in Ag₂Se we observe the onset of “local melting” of the Ag surrounding the SnSe₄ cluster at 50 K below the bulk superionic phase transition. The characteristic features of MS related to microscopic studies of solid electrolytes are fully described.     

High quality weld of melt textured YBCO using Ag doped YBCO junctions

The addition of silver to YBa₂Cu₃O_7−δ (Y123) is well known to decrease its decomposition temperature. This study demonstrates the success in welding large Y123 textured samples with Ag doped Y123 junctions. Attempts to weld two melt textured domains of Y123 by a 1 mm thick layer of Ag doped Y123 are reported. The crucial importance of the initial Y211 excess content in the spacer material is pointed out. Microstructural observations, trapped field measurements and transport critical current density measurements prove that for a given Y211 amount a very high joint quality can be obtained. A transport critical current density as high as 10 kA/cm² is registered through the junction at 77 K and 5 T when the applied field is parallel to the (a,b) planes.     

The strong interaction shift and width of the ground state of pionic hydrogen

The 3p-1s transition in pionic hydrogen was investigated with a high-resolution crystal spectrometer system. From the precisely measured transition energy, together with the (calculated) electromagnetic energy, the strong interaction shift of the 1s state was obtained as ϵ_1s = −7.127 ± 0.028(stat.)± 0.036(syst.) eV (attractive). From the natural line width, measured for the first time, we determine the decaywidth of the 1s state: Γ_1s^(decay) = 0.97 ± 0.10(stat.)± 0.05(syst.) eV. With the recently calculated electromagnetic corrections the s-wave scattering lengths of an isospin symmetric strong interaction are deduced. The scattering length for elastic scattering of a negative pion on a proton is a_{π⁻p→π⁻p}^h = 0.0885±0.00003(stat.)±0.0006(syst.)m_π⁻¹. The scattering lengthe for single charge exchange is found to be a_{π⁻p→π⁰n}^h = −0.136 ± 0.007(stat.) ± 0.003(syst.)m_π⁻¹.The experiment was performed at the Paul Scherrer Institute (PSI) in Switzerland. A focussing crystal spectrometer with an array of bent crystals, the cyclotron trap (a magnetic system designed to increase the particle stop density) and a CCD (charge-coupled device) detector system were employed. The results from the pionic hydrogen experiment — together with those from the pionic deuterium experiment — were used to test the isospin symmetry of the strong interaction. The present data are still consistent with isospin sysmmetry.     

Discussion again of the magnetic and transport property of Ag-doped LaMnO3

Samples La_1−aAg_aMnO₃ (0.05?a?0.50) were sol–gel fabricated. A part of Ag was found to dissociate and run off the samples in sintering process when sintering temperature exceeds 700 °C, resulting in a composite of La_1−xAg_xMnO₃ and MnO₂/Mn₂O₃. The magnetic and transport properties of the composite have been studied. The sample with the nominal composition La_0.7Ag_0.3MnO₃ was found to show the greatest magnetoresistance in the sample group. Detailed analysis on average Mn valence reveals a composite of (La_0.985Ag_0.015MnO₃)_0.776[(MnO₂)_0.590(Mn₂O₃)_0.410]_0.224. Its MR ratio at room temperature exceeds 24% under a field of 1.8 T. A conductivity leap has been observed around a=0.30. It suggests a kind of field-induced fluctuation in percolation in the samples investigated.     

Investigation of the effect of annealing on the magnetic properties of Sn1−xEuxTe single crystals

A study of the effect of annealing on the magnetic properties of single crystals Sn_1−xEu_xTe is reported. The width of the electron paramagnetic resonance line of the crystal is found to decrease upon annealing but its g-value of 1.991 is nearly unaffected. Magnetization results indicate that the pair exchange interaction is weakly antiferromagnetic with a value of −0.67 K for the non-annealed sample and −0.29 K after annealed sample. Susceptibility measurements performed as a function of temperature also indicate the presence of EuTe clusters in the as-grown Sn_1−xEu_xTe crystals. Therefore it was deduced that the Eu²⁺ ions tend to form clusters, particularly pairs, in the as-grown crystal and these clusters disappear after annealing, as the Eu²⁺ ions occupy isolated sites in the SnTe host lattice.     

The thermoelectric power in AgxTiS2 and AgxNiPS3. Part II. The ionic component of the thermoelectric power

The EMF of the isothermal cells: Ag/AgI/Ag_xTiS₂: 0<x<1, T=150–200°C/Ag_xNiPS₃: 0<x<3, T=150–350°C has been measured. From the EMF-x curves the existence ranges of the 2-phase (stage I and II) regions ?0.16<x<0.32 for the Ag/Ag_xTiS₂ system at 190°C; 0.20 < x < 0.50 and 1 < x < 2 for the Ag/Ag_xNiPS₃ system at 400°C - have been determined. The results are sustained by X-ray diffraction and electrical conductivity measurements. From the EMF-T curves the partial enthalpy (ΔH?_Ag) and entropy (ΔS?_Ag) of dissolution of silver in the Ag_xSSE (solid solution electrode) materials were obtained. In the case of Ag_xTiS₂, ΔH?_Ag has a low absolute value, while ΔS?_Ag is distinctly positive. The EMF of the Ag/Ag_xNiPS₃ system also has a positive temperature coefficient. Furthermore, the ionic component of the thermoelectric power, ΔE/ΔT, of the thermogalvanic cells: Ag/AgI/Ag_xSSE/AgI/Ag Ag_xTiS₂: 0 < x < 1, T = 150–200°C( T ) (T+ΔT) Ag_xNiPS₃: 0 < x < 1, T= 150–350°C has been measured. The kinetically important heat of transport of silver ions in the Ag_xSSE materials has been determined in two ways: first from the dependence of the ionic Seebeck coefficient (?_Ag+) on reciprocal temperature; and second from direct calculation, using the data for ?_Ag+ and ΔS?_Ag. The heat of transport is much smaller than the activation enthalpy for Ag⁺-conduction, indicating a high ionic polaron binding energy in these materials.     

A study of the microstructure,thermal properties and wetting kinetics of Sn–3Ag–<Emphasis Type="Italic">x</Emphasis>Zn lead-free solders

Microstructure, thermal properties and wetting kinetics of Sn–3Ag–xZn solders (x = 0.4, 0.6, 0.8, 1, 2 and 4 wt%) were systematically investigated. The results indicate that a small amount of Zn (Zn wt% ≤ 1 wt%) has a rather moderate effect on the microstructure morphology of the Sn–3Ag–xZn solders. The microstructures are composed of a β-Sn phase and the mixture of Ag₃Sn and ζ-AgZn particles. However, the β-Sn phase reduces its volume fraction in the entire microstructure and the intermetallic compounds population increases with the increasing of Zn content. The microstructure is dramatically changed with a further increase in the Zn content. The γ-AgZn phase is formed in a Sn–3Ag–2Zn solder. The ε-AgZn phase is formed in a Sn–3Ag–4Zn solder. The melting temperature and the undercooling of the Sn–3Ag–xZn solder alloys decrease with the increase in Zn content, reach to a minimum value when the content of Zn is 1 wt%, and then increase with further increase in Zn content. The Sn–3Ag–1Zn demonstrates the minimum value of 228.13 °C in the melting temperature and 13.87 °C in undercooling. The wetting kinetics of the main spreading stage features the power law of R ⁿ  ~ t (n = 1), which is controlled by chemical reactions at the triple line.     

Transport coefficients and defect structure of Sb2−xAgxTe3 single crystals

Incorporation of Ag in the crystal lattice of Sb₂Te₃ creates structural defects that have a strong influence on the transport properties. Single crystals of Sb_2−xAg_xTe₃ (x=0.0; 0.014; 0.018 and 0.022) were characterized by measurements of the temperature dependence of the electrical resistivity, Hall coefficient, Seebeck coefficient and thermal conductivity in the temperature range of 5-300 K. With an increasing content of Ag the electrical resistance, the Hall coefficient and the Seebeck coefficient all decrease. This implies that the incorporation of Ag atoms in the Sb₂Te₃ crystal structure results in an increasing concentration of holes. However, the doping efficiency of Ag appears to be only about 50% of the expected value. We explain this discrepancy by a model based on the interaction of Ag impurity with the native defects in the Sb_2−xAg_xTe₃ crystal lattice. Defects have a particularly strong influence on the thermal conductivity. We analyze the temperature dependence of the lattice thermal conductivity in the context of the Debye model. Of the various phonon scattering contributions, the dominant influence of Ag incorporation in the crystal lattice of Sb₂Te₃ is revealed to be point-defect scattering where both the mass defect and elastic strain play a pivotal role.     

The chemical diffusion coefficient in (low temperature)α-Ag2S determined by an electrochemical relaxation method

An electrochemically probed relaxation method has been used to determine the chemical diffusion coefficient, D?, of α-Ag₂+δS. The experiments were performed at 168°C and span the homogeneity range of this phase, which at this temperature is of the order of 10^-5 in δ. D? is found to have values between 0.02 and 0.15 cm² s^-1 and, as a function of nonstoichiometry, to reflect correctly the composition dependence of the thermodynamic factor, d ln a_Ag/d ln c_Ag. Using previously determined data for the thermodynamic factor, the component diffusion coefficient of Ag⁺ at 168°C is found to be D_Ag⁺=(5.4 ± 0.4) × 10^-8cm²s^-1.     

Silver aggregates and twofold-coordinated tin centers in phosphate glass: A photoluminescence study

The optical properties of silver species in various oxidation and aggregation states and of tin centers in melt-quenched phosphate glasses have been assessed by optical absorption and photoluminescence (PL) spectroscopy. Glasses containing silver and tin, or either dopant, were studied. Emission and excitation spectra along with time-resolved and temperature-dependent PL measurements were employed in elucidating the different emitting centers observed and investigating on their interactions. In regard to silver, the data suggests the presence of luminescent single Ag⁺ ions, Ag⁺-Ag⁺ and Ag⁺-Ag⁰ pairs, and nonluminescent Ag nanoparticles (NPs), where Ag⁺-Ag⁰→Ag⁺-Ag⁺ energy transfer is indicated. Tin optical centers appear as twofold-coordinated Sn centers displaying PL around 400 nm ascribed to triplet-to-singlet electronic transitions. The optically active silver centers were observed in glasses where 8 mol% of both Ag₂O and SnO, and 4 mol% of Ag₂O were added. Heat treatment (HT) of the glass with the high concentration of silver and tin leads to chemical reduction of ionic silver species resulting in a large volume fraction of silver NPs and the vanishing of silver PL features. Further characterization of such heat-treated glass by transmission electron microscopy and X-ray photoelectron spectroscopy appears consistent with silver being present mainly in nonoxidized form after HT. On the other hand, HT of the glass containing only silver results in the quenching of Ag⁺-Ag⁰ pairs emission that is ascribed to nonradiative energy transfer to Ag NPs due to the positioning of the pairs near the surface of NPs during HT. In this context, an important finding is that a faster relaxation was observed for this nanocomposite in relation to a heat-treated glass containing both silver and tin (no silver pairs) as revealed by degenerate four-wave mixing spectroscopy. Such result is attributed to Ag NP→Ag⁺-Ag⁰ plasmon resonance energy transfer. The data thus indicates that energy transfer between Ag⁺-Ag⁰ pairs and NPs is bi-directional.