Formation of Amorphous AgI Aggregates Dominating Fast Ion Conductivity in AgI-based Glasses

Precise calorimetry was performed for (AgI)_x(AgPO₃)_1–x and (AgI)_x(Ag₂PO_3.5)_1–x glasses with very high AgI compositions (x0.75). The glasses showed -glass transitions due to the freezing-in of the rearrangement of conductive Ag⁺ ions. Magnitude of the associated heat-capacity jump increased with increasing the AgI composition in the respective glass systems, and was larger in the former system than in the latter when compared at the same AgI composition. All the results were well explained by the amorphous AgI aggregate model for the AgI-based fast ion conducting glasses, indicating the appropriateness of the model for the structure of the glasses with high AgI compositions. The formation of the hypothetical bulk amorphous AgI was also indicated in the glasses at the highest limit of AgI composition.This revised version was published online in November 2005 with corrections to the Cover Date.     

Interactions in multicomponent systems containing surfactants. System silver iodide — methylene blue and sodium dodecyl sulphate

The precipitation and dissolution of AgI in the presence of methylene blue (MB · Cl) and sodium dodecyl sulphate (NaDS) was followed by X-ray diffraction analysis.At high MB · Cl concentration, the absence of AgI precipitates was observed, which is explained by considering the redox process MB⁺ + 2I^– MB^– + I₂. The decrease in I^– concentration causes dissolution or inhibition of growth of solid AgI which is significant at relatively high MB · Cl concentrations. The addition of NaDS causes the disappearance of these effects, which is explained by the incorporation of MB in NaDS micelles.These explanations are supported by the potentiometric measurements using Ag/Ag₂S and Pt electrodes.     

Synthesis and characterization of ambient temperature superionic solids in the composite system CuI–Ag<Subscript>2</Subscript>O–TeO<Subscript>2</Subscript>

The present work deals with the composite system (CuI) _x –(Ag₂O–TeO₂)_{100– x} , where x=30, 35, 40, 45, 50, 55, 60, 65, 70 and 75 mol%, respectively, synthesized by a solid-state reaction route. Powder specimens were analysed using differential scanning calorimetry, X-ray diffraction and Fourier transform infrared techniques. These studies have revealed the formation of Cu₃TeO₆, AgI and/or other phases. The ambient temperature electrical conductivities obtained for the samples using a complex impedance method were found to lie in the range 10^–6–10^–4 Scm^–1, with low activation energies, thus indicating their superionic nature. The typical composition 35CuI–32.5Ag₂O–32.5TeO₂ was identified as the best conducting one, having an electrical conductivity of 6×10^–4 Scm^–1 at 296 K and an activation energy of 0.23 eV. Ion transport number measurements carried out using Wagner's polarization technique as well as by an electromotive force method suggested that silver ions were responsible for the observed transport features of the composite system. Electronic Publication     

Nonstoichiometric Compounds Based on Manganese(III, IV) Oxides with the Birnessite Structure

Nonstoichiometric manganese(III, IV) oxides with the layered birnessite structure were analyzed in terms of the model expressed by the general formula Mn_{1 - q}O,OH)₂(Mn,R)_2q (O,OH,H₂O)_6q ,in which the first part reflects the composition of layers, the second part, the composition of the interlayer spaces of the structure, and q is the coefficient characterizing the relative content of vacant positions in the layers. As R⁺ (R^{2 +}) ions, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Sr^{2 +}, Ba^{2 +}, and Ag⁺ were taken. The H form of birnessite has a particular composition. Experimental data show that metal ions participate in ion exchange with OH groups in the birnessite structure. The increased content of the Li⁺ and Ag⁺ ions in birnessite is attributed to their increased participation in the ion exchange M⁺ + HO-Mn arr; 4 H⁺ + MO-Mn. As the heat treatment temperature is increased, Mn^{3 +} ions are accumulated in the interlayer spaces of the structure, and, above 350°C, the positions of these ions become regular, with transition from the layered birnessite structure to the tunnel structure.     

Effect of Ag+ Concentration on the Uptake Rate of Tracer Elements During the Somatic Embryogenesis of Lycium Barbarum L

Multitracer technique and -ray energy spectrum analysis was used to study the effect of Ag⁺ on the uptake of some tracer metal ions in the somatic embryogenesis of Lycium barbarum L. The results show that in the case of some metal ions the uptake changes are selective, cooperative and interactive in somatic embryogenesis due to Ag⁺ influence. To 50 mg/l Ag⁺ concentration, the uptake and the frequency of somatic embryogenesis increases along with increasing concentration. Ag⁺ could speed up cell differentiation and somatic embryogenesis. Above 50 mg/l Ag⁺ concentration, Ag⁺ has a poisonous effect, influences tracer element absorption and inhibit the frequency of somatic embryogenesis.     

Photochemical properties of Ag ion clusters included within ZSM-5 zeolites prepared by an ion-exchange method

Photoluminescence investigations of the Ag ion-exchanged ZSM-5 (Ag⁺ /ZSM-5) zeolite revealed that a Ag ion cluster (Agⁿ _m ⁺) exists in the pore structure of ZSM-5 exhibiting photoluminesm cence at 380 nm upon excitation at 332 nm. UV irradiation ( = 285 nm) of Ag⁺ /ZSM-5 at 77 K leads to the transformation of Agⁿ _m ⁺ into a different Ag ion cluster (Ag_m ^(n-1)+) which exhibits photoluminescence at 465 nm upon excitation at 315 nm. This photo-transformation of the Ag ion clusters was found to be thermally reversible under vacuum. It was demonstrated that an electron transfer from the photo-excited Al³⁺ -O^2- to Agⁿ _m ⁺ plays a significant role in this process. In the presence of oxygen, UV irradiation of Ag⁺ /ZSM-5 leads to the formation of O₂- instead of an Ag ion cluster (Ag_m ^(n-1)+), suggesting that oxygen acts as an efficient electron scavenger, which interferes with the electron capture of Agⁿ _m ⁺ under UV irradiation at 285 nm.     

New Silver Tellurates – The Crystal Structures of a Third Modification of Ag2Te2O6 and of Ag4TeO5

Single crystals of a third modification of Ag₂Te₂O₆ (denoted as Ag₂Te₂O₆–III) and of Ag₄TeO₅ have been obtained as minor by‐products during hydrothermal phase formation experiments in the system Ag‐Hg‐Te‐O. The crystal structure of Ag₂Te₂O₆–III (P2₁/c, Z = 4, a = 6.4255(10), b = 6.9852(11), c = 13.204(2) Å, β = 90.090(3)°, 1885 independent reflections, R[F² > 2σ(F²)] = 0.0334, wR2(F² all) = 0.0817) comprises tellurium in oxidation states +IV and +VI and is topologically related to the structure of the Ag₂Te₂O₆–I modification, which consists of similar layers and interjacent layers of Ag⁺ cations. Ag₄TeO₅ (C2/c, Z = 8, a = 16.271(2), b = 6.0874(10), c = 11.4373(16) Å, β = 106.730(10)°, 2372 independent reflections, R[F² > 2σ(F²)] = 0.0288, wR2(F² all) = 0.0737) is made up of a layer‐like arrangement of isolated [Te^VI₂O₁₀] double octahedra and of Ag⁺ cations situated both in layers parallel and inside the layers of the anionic moieties.     

Formation mechanism of nanostructured Ag films from Ag2O particles using a sonoprocess

Nanostructured Ag films composed of nanoparticles and nanorods can be formed by the ultrasonication of ethanol solutions containing Ag₂O particles. The present work examined the formation process of these films from ethanol solutions by two different agitation methods, including ultrasonication and mechanical stirring. The mass-transfer process from Ag₂O particles to ethanol solvent is accelerated by the mechanical effects of ultrasound. Ag⁺ ions and intermediately reduced Ag clusters were released into the ethanol. These Ag⁺ ions and Ag clusters provide absorption bands at 210, 275 and 300 nm in UV-vis spectra. These bands were assigned to the absorption of Ag⁺, Ag ₄ ²⁺ and Ag_n (n?≈?3). The Ag_n clusters that readily grow to become Ag nanoparticles were formed due to the surface reaction of Ag₂O particles with ethanol under ultrasonication. The reactions of Ag⁺ ions in ethanol to form Ag nanomaterials (through the formation of Ag ₄ ²⁺ clusters) were also accelerated by ultrasonication.     

Theory of Low-Frequency Scattering of Light by Superionic Glasses with Nanosize Structure

In the Raman spectra of glasses of (AgI) _x (Ag₂O · nB₂O₃)_{1 – x} type, along with so-called boson peak (at frequencies of about 10 cm^–1), a wide central component is pronounced even at room temperature. The component is similar to that in the spectra of crystalline superionic -AgI. The emergence of such a central component in the spectra for glasses containing AgI indicates that size effects, which are associated with the glass structure, can significantly modify the relaxation modes associated with ionic conduction. For the first time, low-frequency spectra of superionic glasses are theoretically analyzed taking into account that, in nanocrystalline AgI, the mobile ion concentration is increased. A theoretical treatment of experimental spectra can provide information on important physicochemical characteristics of such glasses.     

Solvation of ions. Part XXIX. Ionic conductances in acetonitrile-water and pyridine-water mixtures

The limiting conductance of various salts of Na⁺, Ag⁺, Cu⁺, Cu²⁺ and Ph₄As⁺ in acetonitrile-water (AN-H₂O) and pyridine-water (Py–H₂O) mixtures are reported. Single ion values are calculated for AN-H₂O mixtures using the TATB assumption [_o(Ph ₄ As ⁺) = _o(Ph ₄ B ^–)]. The trends observed for the limiting Walden products (_o) of the electrolytes and individual ions are discussed in terms of specific ion-solvent interactions and the structural effects of the solvent mixtures.Deceased, August 30, 1982.     

Thermodynamics of Complexation of Ag+ with 18-Crown-6 in Water-Dimethyl Sulfoxide Mixtures

The stability of complexes and enthalpy of interaction of Ag⁺ ions with 18-crown-6 in waterdimethyl sulfoxide (DMSO) mixtures were determined by calorimetric titration in the range of mole fractions XDMSO from 0.0 to 0.97 at 298.15 K. With increasing concentration of the nonaqueous component in the solvent to XDMSO 0.3, the stability of the complex ion [AgL]⁺ increases, which is followed by a decrease in logK(AgL⁺) to 0.35 plusmn 0.15 at XDMSO 0.97. The exothermic effect of the reaction shows a similar trend. The presence of the extremum in the logK-XDMSO and _r H-XDMSO dependences is explained by the competition of two solvation contributions: destabilization of the ligand with decreasing water content in the solvent and formation of strong solvation complexes of Ag⁺ with DMSO.     

Determination of the composition and the stability constants of complexes of silver(I) with some sulphur containing pyridines a potentiometric investigation

A series of sulphide-containing pyridines of general formula ? (CH₂)_x? S? R where R = CH₃, C₂H₅, CH₂CH₂OH and x = 1, 2 has been prepared and studied potentiometrically in the presence of Ag⁺ in 0.5 M (K)NO₃ medium at 25°C. The complex formation is discussed in terms of the Taft σ*-parameters for the substituents. In acid region, where the complexes AgLH²⁺ and AgL₂H₂³⁺ were formed, coordination occurs through the thioether group. In neutral and alkaline medium their was evidence for the species AgL₂H²⁺, AgL⁺, AgL₂⁺, Ag₂L₂²⁺ and Ag₂L²⁺ in which Ag⁺? S and Ag⁺? bonds are involved. The five membered chelate rings for the AgL⁺ and AgL²⁺ species are found to be more stable than the six-membered ones.     

Synthesis and Structure Determination of Ag5HgSbO6, Comparison with AgHg3SbO6 and Ag5Pb2O6

From solid state reactions of Ag₂O, HgO, and Sb₂O₃ at high temperatures under elevated oxygen pressures a new silver mercury antimonate, Ag₅HgSbO₆, has been obtained. According to a single crystal structure determination Ag₅HgSbO₆ crystallizes in space group P$\bar{3}$ 1c (no. 163) with a = 5.9263(4), c = 12.3023(7) Å, V = 374.18(4) ų, Z = 2, 498 independent reflections, R1 = 0.030, wR2 = 0.059 (I ≥ 2 σ (I). Ag₅HgSbO₆ consists of HgSbO₆ layers, analogous to BiI_3, which are separated by Kagome nets formed by Ag⁺ ions. Perpendicular to these layers and along the c axis linear strings of Ag⁺ ions run through the large voids of the layers. Accordingly, Ag₅HgSbO₆ adopts the Ag₅Pb₂O₆ type of structure where the lead positions are occupied by mercury and antimony alternatingly. The finding of mercury in octahedral coordination, particularly besides the lower charged Ag⁺ cations in linear coordination, which is also highly preferred by Hg²⁺ ions, is rather unexpected. Ag₅HgSbO₆ starts to decompose at 450 °C and, in contrast to subvalent and metallic Ag₅Pb₂O₆, the new compound is charge balanced and semiconducting (ρ = 5.7 Ωcm at ambient temperature, E_a = 0.047 eV).     

Insertion of 3d- and 4f-Elements into Silver Iodide

The interaction of manganese and some 4f-metals (M) with silver iodide is studied. The samples are obtained by sputtering M onto the surface of polycrystalline AgI films (0.2 m, 300 K) in a vacuum. Optical absorption in the samples is interpreted as the insertion of M ions into AgI with the formation of dopants AgI:M. A new phase with an optical bandgap of 3.7 eV emerges in the samples with elevated concentrations of La, Ce, Pr, Nd, Sm, or Dy (n _M/n _Ag 0.1). X-ray diffraction patterns for such samples with Sm correspond to structures with large interfacial distances, for example, 0.99, 0.87, 0.76, and 0.67 nm. In air, AgI forms in the samples with a new phase; this process is hindered by the sputtered protective coatings. According to optical absorption data, X-ray diffraction, and local microanalysis the Mn insertion into AgI is followed by the formation of a new phase (2Ag:Mn:4I), which may belong with solid electrolytes Ag₂MI₄, where nonmagnetic M are known (Zn, Cd, Sn, Hg, Pb).     

Mechanism of silver nucleation upon the radiation-induced reduction of its ions in polyphosphate-containing aqueous solutions

Long-lived (hours to days) silver clusters, Ag ₄ ²⁺ , Ag ₄ ⁺ , Ag ₈ ²⁺ , etc., are formed upon the radiation-induced reduction of Ag⁺ ions in aqueous solutions containing sodium polyphosphate. The efficiency of the cluster formation decreases and the stability of the clusters increase with a rise in the concentration of the polymeric stabilizer. In the course of the aggregation of clusters, their sizes increase, quasi-metallic particles emerge, and the process terminates with the formation of silver nanoparticles. The mechanism of silver nucleation upon the radiation-induced reduction of silver ions in aqueous solutions is discussed.     

Kinetics and mechanism of the oxidation of N-methylformamide and N,N-dimethylformamide by silver (II) in aqueous perchlorate media and comparison with oxidation by CoIII and MnIII

Detailed measurements on the kinetics and stoichiometry of the oxidation of N-methylformamide and N,N-dimethylformamide by aquosilver (II) ions are reported. Four Ag ions are consumed for each amide, and the reaction is first order in [Ag] and first order in [amide]. The reaction is inversely dependent on acidity in the range of 1.5–5.0M HClO₄. The oxidation rate is independent of [Ag^I] and ionic strength. The proposed reaction mechanism and activation parameters are compared with those found for the oxidation of amides by other oxidants such as cobalt(III) and manganese(III).     

Vinyl polymerization initiated by peroxydiphosphate. V. Polymerization of acrylonitrile initiated by peroxydiphosphate-cyclohexanol redox system in the presence of silver ion

The polymerization of acrylonitrile was carried out using peroxydiphosphate-cyclohexanol redox system in the presence of silver ion. The rate of polymerization increases with increasing peroxydiphosphate concentration and the initiator exponent was computed to be 0.5. The rate of polymerization increases with increasing monomer concentration and the monomer exponent was computed to be unity. The plot of R_p vs [Ag⁺]^1/2 was linear, indicating 0.5 order with respect to [Ag⁺]. The reaction was carried out at three different temperatures and the overall activation energy was calculated to be 7.60 kcal/mol. The effect of certain surfactants on the rate of polymerization has been investigated and a suitable kinetic scheme has been pictured.     

Specific Photographic and Luminescent Properties of Sulfur + Gold–Sensitized Silver Halide Emulsions

It was found that the introduction of univalent gold ions at the initial step of sulfur sensitization could lead to a dramatic fall in the light sensitivity (S) and a considerable increase in the intensity of low-temperature ( = 77 K) luminescence (I) of silver sulfide clusters produced by sensitization. An increase in the hold time was accompanied by an increase in S and a decrease in I. The fall in S is associated with the oxidation of the silver moiety in (Ag₂S)_pAg⁺ _k or (Ag₂S)_qAg⁰ _n (q > p) clusters, which are light sensitivity centers. AgBr(I) emulsions subjected to sulfur + gold-sensitization exhibited a flash of IR-excited green luminescence from paired iodine centers. The appearance of this flash is due to the generation of deep electron traps by sulfur–gold sensitization.     

Phase equilibria and the thermodynamic properties of saturated solid solutions of BiTeI,Bi<Subscript>2</Subscript>TeI,and Bi<Subscript>4</Subscript>TeI<Subscript>1.25</Subscript> compounds of the AgI–Bi–Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>–BiTeI system

The phase equilibria of the Ag–Bi–Te–I system in the part AgI–Bi–Bi₂Te₃–BiTeI is studied in the interval of 500–540 K by means of physicochemical analysis. Thermodynamic properties of phases are determined via EMF. Potential-forming processes occur in electrochemical cells (ECCs) of the C|Ag|glass Ag₃GeS₃I|D|C structure (where C denotes inert (graphite) electrodes; Ag, D denotes ECC electrodes; D denotes four-phase alloys of the AgI–Bi–Bi₂Te₃–BiTeI system; and Ag₃GeS₃I glass is the selective Ag⁺ conducting membrane). Linear dependences of the EMFs of cells Е(Т) in the interval of 505–535 K are used to calculate the values of the thermodynamic functions of BiTeI, Bi₂TeI, and Bi₄TeI_1.25 phases saturated over silver.     

Synthesis and metal extraction behavior of pyridine and 1,2,4-triazole substituted calix[4]arenes

Three series of heterocycle substituted calixarenes, derivatized at lower and upper rim, were synthesized and successfully evaluated for metal extraction towards alkali, alkaline, transition and heavy metal ions. The presence and placement of sulfur, heterocycle functionality at upper/lower rim played a crucial role toward the extractability and selectivity of metal ions. The lower rim substituted calixarenes have shown high extractability and poor selectivity. In contrast to this, upper rim substituted calixarenes exhibited good selectivity. Moreover, sulfur functionalized calixarenes have shown better selectivity for heavy metal ions than alkali and alkaline metal ions. Among upper rim substituted calixarenes, 17 and 18 were found to be suitable for Na⁺, K⁺ and Ag⁺, 19,13 for heavy metal ions i.e., Pb²⁺, Hg⁺, Hg²⁺ and Ag⁺, and 11,12 for Pb²⁺ and Ag⁺ only.