Ag Se Research Articles

Polynuclear silver compound formed from aggregation of Se 2− and Ag(I)-thiolate complex. Synthesis, structure and spectroscopic characterization of Ag 11( μ5-Se)( μ4-Et 2NCS 2) 3( μ3-Et 2NCS 2) 6

The reaction of Et 2NCS 2Ag with [Et 4N] 2MoSe 4 or Na 2Se in DMF/CH 3CN gave rise to a polynuclear silver cluster compound Ag 11( μ 5-Se)( μ 4-Et 2NCS 2) 3( μ 3-Et 2NCS 2) 6, which crystallized in trigonal space group R3 c with a = 18.633(6), c = 43.032(12) A ̊ , and Z = 6 . The molecule possesses a crystallographic C 3 symmetry axis and three equivalent units of Ag 3(Et 2NCS 2) 3. The average AgAg and AgSe distances are 3.004(3) and 2.801(4) Å, respectively. The structure is discussed together with its IR, UV-Vis and 1H NMR spectra. The compound shows an intense emission with λ max at 565 nm in the solid state. Cyclic voltammetry and thermal gravimetric analysis of the title compound are also reported.

Influence of an electrical field on optical recording in chalco-halide glasses

The present investigations concern holographic recording on thin films of the systems Se–Ag–I and Ge–Se–AgI. After optimization of compositions and intensity of the laser beam for recording on these films, experiments are conducted on a three-layer structure—SnO 2–chalco-halide–Au. Various bias voltages were applied on this structure in the process of optical recording. It is established that depending on the voltage bias the sensitivity of the layers can be increased. The mechanism of this process is discussed in terms of the occurrence of defects in the glassy film, as well as the processes in the heterojunction SnO 2–chalco-halide film under different electric field polarities.

Nickel and selenium grain boundary solute diffusion and segregation in silver

For the first time, the grain boundary (GB) solute diffusion of Ni and Se in Ag polycrystals was investigated systematically by the radiotracer serial sectioning technique using 63Ni and 75Se isotopes. Measurements in the temperature ranges 589–989 K for Ni and 371–877 K for Se were carried out in Harrison's type B regime at high temperatures and in type C regime at low temperatures. In the B regime, the product sδD GB was determined ( s being the solute GB segregation factor, δ the GB width, D GB the GB diffusion coefficient), while in the C-regime D GB values were measured directly. The solid solubility of both solutes, Ni and Se, in Ag is very small. The equilibrium phase diagrams, however, are quite different: Se forms an intermetallic compound whereas Ni does not form any compound with Ag, which indicates dominating Se–Ag and Ni–Ni bonds, respectively. Comparing the solute D GB values with C regime measurements of GB self-diffusion in Ag, a drastic decrease of the Ni diffusivity and an increased activation enthalpy of Ni diffusion, H GB Ni, in Ag GBs is observed. This behaviour is discussed in terms of repulsive Ni-vacancy interactions and decreased jump frequencies of the Ni atoms which are mainly located at low energy positions in the GB. The measured D GB values of Se, on the other hand, are comparatively close to GB self-diffusion, whereas H GB Se is again larger than H GB Ag of GB self-diffusion. This behaviour is explained in terms of the formation of “embryos” of two-dimensional phases at high energy GB sites. Combining the obtained sδD GB and D GB values and assuming δ=0.5 nm, the GB segregation factors and segregation enthalpies of Ni ( H s Ni=−39.7 kJ/mol) and Se ( H s Se=−21.4 kJ/mol) in Ag were evaluated.

Structure of Ag–As–Se glasses with high silver content X-ray diffraction and reverse Monte Carlo simulations

The structure of ternary Ag–As–Se chalcogenide glasses (Ag 2Se) x (AsSe) 1− x , where x=0.27, 0.39 and 0.54, have been studied by X-ray diffraction radial distribution function analysis. The average coordination number increases from 2.5±0.1 to 3.5±0.1 with increasing Ag content, accompanied by a decrease of the medium-range order on the 3–8 Å scale. Using the experimentally determined structure factors, the first three-dimensional models of the structure of Ag–As–Se glasses are constructed by the reverse Monte Carlo (RMC) method. The RMC simulations indicate that the Ag–Se coordination number is 2.5±0.2 in the whole compositional range studied. On the contrary, the average coordination number of Se increases from about 2.8 to 4.0 with increasing Ag content. First estimate of the As–As coordination number, n As As=0.6, in Ag–As–Se glasses is made. With increasing silver content the structure changes from a network of molecular-like units (AsSe 3 and AgSe 3 pyramids and AgSe 4 tetrahedra) connected via –Ag–Se–Ag– and –As–Se–As– chain-like elements to overcoordinated three-dimensional cluster-type structure.

Comparison of Magnetic and Electrical Properties of Liquid Ag–Te and Ag–Se Alloys

Measurements of the magnetic susceptibility, electrical conductivity and thermo-electric power of liquid Ag–Te and Ag–Se alloys have been extended to the whole composition range. The susceptibility data of liquid Ag–Se alloys near the stoichiometry are very similar to those of liquid Ag–Te alloys. However, the composition dependence of conductivity for liquid Ag–Se and Ag–Te systems exhibits a sharp peak and a deep minimum at the stoichiometry, respectively. The thermopower data of liquid Ag–Te and Ag–Se alloys show a p - n transition at c =0.315 and 0.360, respectively. The conductivity and thermopower of liquid Ag–Se and Ag–Te alloys near the stoichiometry were analyzed by using the equations derived from the Kubo-Greenwood formula.

Structure, dynamics, and electronic structure of liquid Ag-Se alloys investigated by ab initio simulation.

Ab initio molecular-dynamics simulations have been used to investigate the structure, dynamics and electronic properties of the liquid alloy Ag(1-x)Se(x) at 1350 K and at the three compositions x=0.33, 0.42 and 0.65. The calculations are based on density-functional theory in the local density approximation and on the pseudopotential plane-wave method. The reliability of the simulations is confirmed by detailed comparisons with very recent neutron diffraction results for the partial structure factors and radial distribution functions (RDF) of the stoichiometric liquid Ag2Se. The simulations show a dramatic change of the Se-Se RDF with increasing Se content. This change is due to the formation of Se clusters bound by covalent bonds, the Se-Se bond length being almost the same as in pure c-Se and l-Se. The clusters are predominantly chain-like, but for higher x a large fraction of 3-fold coordinated Se atoms is also found. It is shown that the equilibrium fractions of Se present as isolated atoms and in clusters can be understood on a simple charge-balance model based on an ionic interpretation. The Ag and Se diffusion coefficients both increase with Se content, in spite of the Se clustering. An analysis of the Se-Se bond dynamics reveals surprisingly short bond lifetimes of less than 1 ps. The changes in the density of states with composition arise directly from the formation of Se-Se covalent bonds. Results for the electronic conductivity obtained using the Kubo-Greenwood approximation are in adequate agreement with experiment for l-Ag2Se, but not for the high Se contents. Possible reasons for this are discussed.

Structure of the AgAsSe chalcogenide glasses: the AsSeAg 2Se line

X-ray absorption spectroscopy (EXAFS and XANES) was used to determined the local structure of AgAsSe glasses that belong to the (Ag 2Se) x (AsSe) 1− x line of the phase diagram. Each of the three atoms has been excited. At the arsenic K edge, the one-shell fit shows the existence of AsSe 3 units for all compositions and an invariant Debye-Waller factor when silver content increases. At the selenium K edge, the fit shows that the total number of first neighbours around the selenium atom varies from nearly three (as in the Ag 3AsSe 3 crystalline compound) for the silver-enriched glass ( x = 0.43) to two (as in the As 4Se 4 glass or crystalline phase) for the silver-poor glasses. The radial distribution function for the silver K edge at room temperature shows a unique contribution related to the AgSe pairs. However, at low temperature (35 K) a second peak appears. The qualitative interpretation of the XANES part of the absorption spectra is in good agreement with the present structural investigation. Based on these results a tentative model is given.

Glass formation in the Se Ag I system

The glass-forming region in the Se-Ag-I system is determined. The glassy phases in it are situated in the Serich side of the triangle diagram contain up to 22.5 at.% Ag and up to 12.5% I. The glassy state of the phases is proved by X-ray and electron microscope analysis. Investigations are carried out on the basic properties of the glassy phases obtained-glass transition temperature, microhardness, density, mean molar volume and chemical resistance, discussed in terms of their composition. A structural model of the glasses is proposed on the basis of these properties and the X-ray analysis.

Synthesis, x-ray structure determination, and spectroscopy of the silver(I) polyselenides [(Ph4P)Ag(Se4)]n, [(Me4N)Ag(Se5)]n, [(Et4N)Ag(Se4)]4, and (Pr4N)2[Ag4(Se4)3]. Extreme structure dependence on counterion size

The reaction of sodium pentaselenide with silver nitrate in dimethylformamide (DMF) was investigated. The addition of various counterions, Ph 4 P + , Me 4 N + , Et 4 N + and Pr 4 N + to this common reaction solution resulted in the isolation of four new soluble silver(I) polyselenide complexes, [(Ph 4 P)Ag(Se 4 )] n , [(Me 4 N)Ag(Se 5 )] n , [(Et 4 N)Ag(Se 4 )] 4 and (Pr 4 N) 2 [Ag 4 (Se 4 ) 3 ]

Effect of alloying with silver on intermediate-range order in bulk germanium diselenide glasses

Neutron diffraction, inelastic scattering and Raman scattering measurements have been made on well characterized samples of GeSe 2 and Ag 4Ge 3Se 9 glass. The alloying with Ag causes pronounced effects on both static and dynamic structure, the former characterized by a sharp decrease in the amplitude of the first sharp diffraction peak and the latter by a reduction in the number of modes corresponding to the v 3 vibrations of a Ge(Se 1/2) 4 tetrahedron and an increase in the number between v 4 and v 1. The neutron data are compared with a model based on the consideration of elementary structural units such as Ge(Se 1/2) 4 and Ag(Se 1/2) 3. The Raman spectrum is characterized by the disappearance of the “companion” line in the v 1 breathing mode upon doping with silver.

Counterion Dependent Structural Diversity in Silver Polyselenides; Structures of the New Complex Anions [Ag(Se4)], [Ag(Se5)] and [Ag4(Se4)3]2⊖

Large cations such as Ph4P⊕ and Pr4N⊕ favor a trigonal planar coordination, small ones such as Me4N⊕ a tetrahedral coordination of Ag⊕ in silver polyselenides. In the novel complex {[Me4N][Ag(Se5)]}n one-dimensional infinite [Ag(Se5)] macroanions are present in which the Se ligands bridge three Ag atoms (see 1).

Structural and dynamical correlations in Ag2Se: A molecular dynamics study of superionic and molten phases

We study the structural properties, single-particle dynamics, and the charge transport in superionic and molten Ag2Se using the method of molecular dynamics. The calculations are based on a model of interionic potentials in which the ions interact through Coulomb interaction, steric repulsion, and charge–dipole interaction due to the large electronic polarizability of the selenium ions. In the superionic phase the Ag ions diffuse through a stable bcc lattice of Se atoms. Structural and dynamical correlations are studied at five temperatures in the superionic phase and three temperatures in the molten phase. Among the structural correlations the results are presented for partial pair distribution functions, coordination numbers, partial structure factors, bond angle distributions, and the wave vector and temperature dependence of the Bragg intensities. Detailed comparison with the neutron and x-ray single crystal diffraction results are made whenever possible. Diffuse neutron and x-ray scattering is calculated and investigated in detail in the vicinity of q0=(1.6,1,0). It is shown that the anisotropic disks of intensity arise entirely due to the collective motions of silver ions and that these correlations manifest in the q space at a point where the Se–Ag partial structure factor is nearly zero. The calculated temperature dependence of the self-diffusion constant of silver is in good agreement with the tracer diffusion measurements. The spectra of velocity autocorrelation functions and the frequency dependent ionic conductivity are calculated. The Haven’s ratio, derived both from the calculated self-diffusion and zero frequency limit of the ionic conductivity, is in good agreement with the experimental results of Okazaki. In the molten phase the calculated neutron structure factor is compared directly with the neutron diffraction experiments of Susman et al. The results for self-diffusion of silver and selenium ions in the molten phase and the frequency dependent ionic conductivity are also discussed.

X-ray crystal structure of the quaternary semiconductor compound: AgGaSn()Se 4

This is the first diffractometric X-ray structural study of a quaternary semiconductor compound. Crystals of AgGaSn()Se 4 are tetragonal with space group I 4 2d and cell dimensions: a = 5.853(2) A ̊ , c=10.820(4) A ̊ , V=370.7 A ̊ 3 , Z=2, Dx = 5.419 g/ cm 3. The structure was refined by full matrix anisotropic-isotropic least-squares technique using data taken at room temperature with MoK α radiation, λ = 0.71069 A ̊ ( μ = 281.1 cm -1, F(000) = 528). Final value of R = 0.0455, Rw = 0.0396 for 185 unique reflections with I #62; 3σ(I). The structure determination has shown that Se atom occupies the general position (0.2530 0.2749 0.1398) with an occupation factor of 0.5; Ag and () share the position (0 0 0) and Ga and Sn the (0 0 1 2 ). The crystalline structure of the studied quaternary compound presents disordered tetrahedral (Ag)(Ga)Se(Sn)() units with bond distances (Sn,Ga)-Se = 2.471 (2) A ̊ ; Ag-Se = 2.659 (2) A ̊ and ()-Se = 2.314(2) A ̊ . The fundamental difference between this structure and the chalcopyrite one is the anions position: e vs d (Wyckoff notation) respectively. The structure can also be described as I 4 2d coming from an I 4 structure comprised of distorted tetrahedral (Ag)(Ga)Se(Sn)() units disordered in such a way that a 2 ( z= 1 8 ) is generated.

Chemical Shifts of Photoelectron and Auger Lines in Ag- or Cu-Doped Amorphous GeSe2 and As2Se3

Chemical shifts of the Ag 3d5/2,3/2, Cu 2p3/2,1/2, Ge 3d, 3p3/2,1/2, As 3d, 3p3/2,1/2, and Se 3d, 3p3/2,1/2, photoelectron lines, and the AgM4,5N45N45, GeL3M45M45 and CuL3M45M45 Auger lines are measured for Ag and Cu films, and amorphous films of Ge, As, Se, GeSe2, As2Se3, Ag-doped GeSe2, Ag-doped As2Se3 and Cu-doped As2Se3. The chemical shifts of Ge, Ag and Cu photoelectron lines are corrected for by an extra-atomic relaxation energy obtained from the chemical shifts of Ge, Ag and Cu Auger lines. These results are explained for in view of the electronegativity scales. The chemical shifts in Ag-doped GeSe2 are treated in accordance with the valence shell potential model; Ag–Se and Ge–Se bonds are attributed to covalent bonds rather than ionic bonds in terms of the amounts of ionic character and the electronegativity differences.

The synthesis and structures of silver complexes with trimeric thioformaldehyde and trimeric selenoformaldehyde

The compounds [(CH 2X) 3 2Ag]AsF 6 (X = S, Se) have been prepared from (CH 2X) 3 and AgAsF 6 in liquid So 2 as minor and major products respectively. Both X-ray crystal structures were determined X = S: P2 1/ c, a 8.579(2), b 20.618(4), c 9.821(2) Å, β 107.95(2)°, R = 0.078 for 2439 reflections. The silver atom shows irregular trigonal coordination, with AgS 2.515, 2.532, 2.764 Å; the extended cation structure is a chain polymer X = Se: C2/ c, a 28.80(4), b 9.42(1), c 22.40(4) Å, β 137.4(1)°, R = 0.106 for 1676 reflections. The structure contains isolated [(CH 2Se) 3 2Ag] + cations, all six selenium atoms coordinating silver (AgSe 2.78–3.05 Å).

Un nouveau matériau, Ag 9GaSe 6: Etude structurale de la phase α

α-Ag 9 GaSe 6 is cubic, space group F 43m , with a = 11.126(2) Å and Z = 4. The diffraction pattern at 20°C using MoK α radiation was collected with an automatic four-circle diffractometer. The structure was determined by beginning from the low-temperature structure (βAg 9GaSe 6). An anisotropic full-matrix least-squares refinement was performed yielding a final R of 0.063 for the 103 reflections actually measured. The four Ga atoms and eight Se atoms are located on a 16( e) position. All the GaSe bonds are 2.366(10) Å. The Ag atoms are equally distributed on three sets of positions: two 48( h) and one 96( i). Among the 36 Ag atoms, 24 are bound to 3 Se atoms in an almost planar triangular arrangement (2.43(4) < AgSe bonds < 2.85(7) Å), and 12 are in a tetrahedron of 4 Se atoms (2.68(5) < AgSe bonds < 2.93(5) Å).

The Magnetic Susceptibilities of Some Liquid Chalcogenides

AbstractThe magnetic susceptibilities for seven binary alloy systems (SnTe, SnSe, InTe, InSe, AgTe, AgSe and AgS) are measured as a funtion of temperature and composition. The diamagnetic susceptibilities of these systems fall rapidly on melting except for the InSe system, and decrease gradually with increasing temperature in the liquid state. The change of magnetic susceptibility at the melting point is considerably large in SnTe and SnSe, while rather small in Ag2X (X: Te, Se, and S). Diamagnetic maxima appeared around the stoichiometric composition (SnTe, SnSe, In2Te3, In2Se3, and Ag2X) and correspond well to minima in the electrical conductivity reported previously. These data suggest that electrons tend to localize at these compositions. Relationships between the degree of electron localization and the chemical bonding are discussed using the bond orbital approximation for the diamagnetism of semiconductors. The result indicates that the electron localization is stongly influenced by the bonding nature of anions.

ChemInform Abstract: KINETIC STUDIES ON THE SELENIZATION OF SILVER

AbstractDie Kinetik der Selenidbildung von Ag mit flüssigem Se, die Geschwindigkeit der A Grenzflächenreaktion Ag/Agz Se, die Ionenleitfähigkeit von Ag in der Agzse‐Schicht, die Kinetik der Grenzflächenreaktion Agz Se/Se(?) sowie die Gesamtreaktionsgeschwindigkeit werden bestimmt.

Kinetic Studies on the Selenization of Silver

Abstract In order to elucidate the kinetics of selenization of silver by liquid selenium, the Ag/Ag2Se interface reaction rate, the ionic conductivity of Ag+ in Ag2Se layer, the Ag2Se/Se(1) interface reaction rate, and the over-all reaction rate were determined. The Ag/Ag2Se interface reaction rate was found to be given by υ=1.6×10^9{exp(-32300/RT)}(a_Se) eqv cm^-2·s^-1 The following mechanism was proposed for the interface reaction. 2Ag(Ag)+Se(Ag_2Se)→2Ag^+(Ag_2Se)+Se^2-(Ag_2Se) It was found that the driving force of the Ag2Se/Se(1) interface reaction is very small and Ag2Se is in equilibrium with Se(1). On an assumption that the over-all reaction is controlled by both the Ag/Ag2Se interface reaction and the diffusion of Ag+ in Ag2Se, the over-all reaction rates were calculated. The results agree with the observed ones.

The complexing characteristics of insoluble selenides. 1. Silver selenide

The aqueous solubility of the system silver selenide has been investigated in an inert atmosphere of nitrogen at a unit molar ionic strength and constant temperature of 25° C. The experimental evidence indicates the formation of two aqueous species [Ag2(HSe)(OH)], and [Ag(Se)2(OH)]4− in contact with the precipitated selenide in different regions of acidity. The former exists in acidic medium and has a pβ value of 48.49 ± 0.10 while the latter is stable only in alkaline conditions and has a pβ value of 24.07 ± 0.19. A mathematical treatment has been elaborated to identify and calculate the stability constants of such selenide complexes formed through a heterogeneous equilibrium.