129I-Mössbauer study of diffusion effects in the superionic conductor Ag3SI

The superionic conductor Ag₃SI was studied by¹²⁹I-Mössbauer spectroscopy in the rhombohedral γ-phase and in the cubic β-phase at temperatures between 4.2 K and 180 K. In the low-temperature γ-phase, one observes well below the γ-β phase transition at 157 K a motional-narrowing-like decrease of the electric-quadrupole interaction, roughly linear with temperature, which points to a diffusional motion of the Ag⁺ ions already in the γ-phase. Diffusional effects are also reflected by anomalous decrease of thef-factor in the same temperature region, which originates from a restricted short-range diffusional displacement of the iodide ions induced by the hopping Ag⁺ ions.     

129I-Mössbauer spectroscopic study of iodide-containing chalcogenide glasses

¹²⁹I-Mössbauer spectroscopy was used to study the short-range order in I-containing chalcogenide glasses. It was found that AsXI glasses, where X=S or Se, are molecular solids composed from molecular units of arsenic iodide and arsenic chalcogenide. The local environment of iodide ions in ternary superionic conducting glasses AgI?Ag₂S?As₂S₃ is similar to that in the crystalline superionic conductor Ag₃SI and differs distinctly from iodide local order in binary vitreous alloys AgI?As₂S₃ and crystalline AgI.¹²⁹I-Mössbauer spectra of all glasses were fitted satisfactory, when a distribution of the electric-quadrupole coupling constant is taken into account.     

129I-Mössbaurer study of superionic glasses AgI−Sb2S3: Local structure and diffusion effects

The local environment and the short-range diffusional displacements of the iodide ions induced by the hoppingAg ⁺ ions have been studied inAgI?Sb ₂ S ₃ superionic glasses using¹²⁹ I-Mössbauer spectroscopy in the temperature range 4.2 K to 240 K. It was found that the nearest neighbours of the iodide ions are only silver ions; the local environment of iodide is therefore close to that in the crystalline superionic conductorAg ₃ SI. Diffusion effects are observed above 140 K by characteristic changes in isomer shift, electric-quadrupole interaction and recoil-free fraction. The derived activation energy for theAg ⁺ ion local hopping is 2 times larger than that of crystallineAg ₃ SI.     

Heat capacity of the solid electrolyte Ag13[NMe4]2I15 between 80 and 300 K

Ag₁₃[NMe₄]₂I₁₅ is shown to undergo a transition at 150 K and to have a heat capacity that exceeds the sum of the heat capacities of its components AgI and Me₄NI, above 150 K. This is consistent with disordering of Ag⁺ ions. The experimental excess entropy is substantially below that calculated on the basis of random occupancy of crystallographically identified sites, suggesting that even at room temperature, Ag⁺ distribution among sites is not random.     

Photochromism in Cu-and Ag-doped Bi<Subscript>12</Subscript>SiO<Subscript>20</Subscript> crystals

The equilibrium and photoinduced absorption spectra of copper-and silver-doped Bi₁₂SiO₂₀ crystals are studied. It is demonstrated that the impurity absorption is due to Ag²⁺, Ag⁺, Cu³⁺, Cu²⁺, and Cu⁺ ions occupying almost octahedral Bi³ positions. A mechanism of photochromism is suggested, involving changes in the charge states of copper and silver impurity ions according to schemes Cu²⁺-e → Cu³⁺ and Ag⁺-e → Ag²⁺.     

Chemical effects on x‐ray fluorescence yield of Ag+ compounds

X‐ray fluorescence measurements were carried out for silver metal and a number of silver compounds containing Ag⁺ ions such as Ag₂CO₃, Ag₂SO₄, AgNO₃, AgCl, AgBr and AgI using 59.6 keV γ‐rays, emitted from ²⁴¹Am, as the excitation source, to evaluate the value of Kβ/Kα x‐ray intensity ratio. For silver metal the value of this parameter is found to be 0.206 ± 0.003 and wide variations, 0.190 ≤ Kβ/Kα≤ 0.207, were observed for these compounds. The results are explained in terms of the charge transfer occurring between Ag⁺ and the coordinating anions. Copyright © 2005 John Wiley & Sons, Ltd.     

Dielectric Dispersion in Ag6I4WO4 and Ag6I4CrO4 solid elecrolyte thin films

This paper deals with the dielectric measurements made on the electrodeposited films of the solid electrolyte systems Ag₆I₄WO₄ and Ag₆I₄CrO₄. Dielectric dispersion studies have been carried out in the frequency range 10³ to 10⁵ Hz at various temperatures (300 to 400 K). The frequency dependence of dielectric constant has been attributed to the interfacial polarization of Ag⁺ ions in these compounds. The observed dielectric loss behavior suggest a Debye-type of relaxation in these systems.     

Influence of silver on the Sm<Superscript>3+</Superscript> luminescence in “Aerosil” silica glasses

The introduction of silver into the samarium-containing silica glasses prepared by the original solgel method leads to the formation of complex optical centers involving samarium ions and simple and/or complex silver ions. These centers are characterized by the effective sensitization of Sm³⁺ luminescence by Ag⁺, (Ag₂)⁺, and (Ag⁺)₂ ions according to the exchange mechanism for, at least, Sm³⁺-Ag⁺ centers. The formation of Sm-Ag centers is accompanied by an increase in the concentration of nonbridging oxygen ions, which prevent the reduction of silver ions by hydrogen. Silver nanoparticles formed in small amounts upon this reduction are effective quenchers of luminescence from the corresponding excited states of Sm³⁺ ions.     

Investigations on field desorption products from silver surfaces by mass spectrometry

Field evaporation of silver and field desorption of silver surface compounds were investigated by analysing positive ions with a mass spectrometer. In particular, the well known adsorption states of oxygen, and further the interactions of H₂O, NH₃, H₂, CO and CH₄ were measured in the field ion mass spectrometer under steady state fields of > 0.1 V/Å with a sensitivity of < 0.1 ions s^?1 and at temperatures between 80 °K and 425 °K. Although oxygen is usually chemisorbed at Ag surfaces, no AgO⁺, AgO⁺₂ or other Ag-O compounds could be detected as positive ions, Ag⁺ and O₂⁺ are the only observed ions at best image fields in oxygen up to fields of field evaporation of Ag⁺(≈ 2.2 V/Å). Even after the actual adsorption of oxygen with zero-field (6 × 10⁵ Langmuir at 10^?3 Torr) at 323 °K and 473 °K and subsequent application of the desorption field at 210°K no silver-oxygen compounds were found in positive ionic form. Small quantities of AgO⁺ and AgO⁺₂ were only formed — besides Ag(H₂O)_x⁺ complexes — if atomic oxygen was supplied by the field induced dissociation of water.Gases which do not adsorb on silver under zero-field conditions (H₂, CO, CH₄, N₂) yield the ions Ag(H₂)_n, Ag(CO)_n⁺, n=1, 2; AgCH₄⁺, AgN₂⁺. The situation with H₂O and NH₃ is more complicated: Molecular ions [Ag(H₂O)_n]⁺·mH₂O, n=1,…, 4, m=1,…, 8 and [Ag(NH₃)_n]⁺·mNH₃, n=1, 2, m=1,…, 6 are found besides Ag⁺.From the temperature and field dependence conclusions are drawn about the mechanisms of evaporation and formation of ionic surface complexes. The activation energies of evaporation of Ag⁺ are found to depend on the square root of the field strength. In general, the generation of surface compounds can be described by field induced reactions rather than usual gas adsorption.     

Coupled motions of ions and electrons in some superionic conductors: An ab initio molecular dynamics study

The dynamic and electronic properties of mobile ions in the superionic conductors CuI and Ag₂Se are studied by means of ab initio molecular dynamics simulations. The superionic behavior of these materials is successfully reproduced by our simulations. To investigate the bonding nature of these materials, the spatial distributions of the electrons and the time evolutions of the gross charge of the ions are calculated by the population analysis method. The time evolution of the electronic states around the mobile ions indicates that the local chemical bonding properties change accompanying the diffusive motion of mobile ions. It is also shown that the 4p-electron populations of Cu in CuI and 5p-electron populations of Ag in Ag₂Se change largely with time, while the s- and d-electron populations depend weakly on time.     

Non-interferometric transient quantitative phase microscopy for ultrafast engineering

Lead-free piezoelectric ceramics Bi_0.5(Na_1-x-yK_xAg_y)_0.5TiO₃ [BNKAT(x/y)] have been synthesized by the mixed oxide method. The effects of the amount of K⁺ and Ag⁺ on the electrical properties were examined. X-ray diffraction patterns indicate that K⁺ and Ag⁺ ions partially substitute for the Na⁺ ions in Bi_0.5Na_0.5TiO₃ and form a solid solution during sintering. At room temperature, the ceramics exhibit good performances with piezoelectric constant d₃₃=189 pC/N, electromechanical coupling factor k_p=35.0%, remanent polarization P_r=39.5 μC/cm², and coercive field E_c=3.3 kV/mm, respectively. The curves of the dielectric constant ε_r and loss tangent tan δ versus temperature show that the transition temperature from ferroelectric to anti-ferroelectric phase decreases with increasing the K⁺ content for the compositions researched. The dependencies of k_p and polarization versus electric (P–E) hysteresis loops on temperature reveal that the depolarization temperature T_d of BNKAT(0.15/0.015) ceramics, which have good piezoelectric properties (d₃₃=134 pC/N, k_p=32.5%) and strong ferroelectricity (P_r=39.5 μC/cm², E_c=4.1 kV/mm) at room temperature, is above 160 °C. PACS 77.22.-d; 77.65.Bn; 77.80.Bh; 77.80.Dj; 77.84.Dy     

Coordination and solvation of noble metal ions: Infrared spectroscopy of Ag+(H2O)n

Vibrational spectra of mass-selected Ag⁺(H₂O)_n ions are measured by infrared photodissociation spectroscopy and analyzed with the aid of density functional theory calculations. Hydrogen bonding between H₂O molecules is found to be absent for cold Ag⁺(H₂O)₃, but detected for Ag⁺(H₂O)₄ through characteristic changes in the position and intensity of OH-stretching transitions. The third H₂O coordinates directly to Ag⁺, but the fourth H₂O prefers solvation through hydrogen bonding. The preference of the tri-coordinated form is attributed to the inefficient 5s–4d hybridization in Ag⁺, in contrast to the efficient 4s–3d hybridization in Cu⁺. For Ag⁺(H₂O)₄, however, di-coordinated isomers are identified in addition to the tri-coordinated one.     

Metastable fragmentation of silver bromide clusters

The abundance spectra and the fragmentation channels of silver bromide clusters have been measured and analyzed. The most abundant species are Ag_nBr_{n - 1} ⁺ and Ag_nBr_{n + 1} ^- and Ag₁₄Br₁₃ ⁺ is a magic number, revealing their ionic nature. However, some features depart from what is generally observed for alkali-halide ionic clusters. From a certain size, Ag_nBr_{n - 1} ⁺ is no more the main series, and Ag_nBr _{n - 2, 3} ⁺ series become almost as important. The fast fragmentation induced by a UV laser makes the cations lose more bromine than silver ions and lead to more silver-rich clusters. Negative ions mass spectra contain also species with more silver atoms than required by stoichiometry. We have investigated the metastable fragmentation of the cations using a new experimental method. The large majority of the cations release mainly a neutral Ag₃Br₃ cluster. These decay channels are in full agreement with our recent ab initio DFT calculations, which show that Ag⁺-Ag⁺ repulsion is reduced due to a globally attractive interaction of their d orbitals. This effect leads to a particularly stable trimer (AgBr)₃ and to quasi-planar cyclic structures of (AgBr)_n clusters up to n = 6. We have shown that these two features may be extended to other silver halides, to silver hydroxides (AgOH)_n, and to cuprous halide compounds. Received 9 November 2000 and Received in final form 25 January 2001     

Spin resonance of conduction electrons and EPR of localized moments in a low-dimensional organic conductor [Pd(dddt)2]Ag1.5Br3.5

The EPR spectra of a quasi-two-dimensional organic metal [Pd(dddt)₂]Ag_1.5Br_3.5 contain signals due to the spin resonance of conduction electrons (CESR) and signals due to the localized magnetic moments of Ag²⁺. The system of Ag²⁺ ions exhibits a strong indirect antiferromagnetic exchange interaction characterized by the Weiss constant Θ=−280(25) K, which leads to magnetic ordering at a temperature of T ₀=70(10) K. The same temperature T ₀ corresponds to a strong anomaly in the CESR linewidth. The observed anomaly in the CESR linewidth, as well as some features of the temperature dependence of conductivity in the system studied, are explained by the interaction between conduction electrons and Ag²⁺ ions localized in the anion layers (π-d interaction) and by antiferromagnetic ordering of the spins of Ag²⁺ magnetic ions.     

Brownian motion of a particle in a double well potential

The frequency dependent mobility of a Brownian particle moving in a double well potential is calculated for different damping parameters and temperatures by means of continued fraction approximations. These results are remarkably well reproduced by a simple memory function ansatz. Applications to the motion of Ag⁺ ions in Ag₃SX(X =I, Br) crystals are indicated.     

Dissociation channels of silver bromide cluster Ag<Subscript>2</Subscript>Br,silver cluster Ag<Subscript>3</Subscript> and their ions studied by using alkali metal target

Various dissociation channels of silver bromide cluster ion Ag₂Br⁺ and silver cluster ion Ag₃ ⁺ were observed in high-energy collisionally-activated dissociation (CAD) using a Cs target. The fragment patterns of the high-energy CAD were compared with those of the metastable dissociation and low-energy CAD. The difference in the fragment patterns between the high-energy CAD and the other dissociation methods was explained in terms of the internal energy distributions. The dissociation mechanisms of neutral silver bromide cluster Ag₂Br and silver cluster Ag₃ were also investigated by charge inversion mass spectrometry using the Cs target. While the fragment ions AgBr^- and Ag₂ ^- were dominantly observed in the charge inversion spectrum of Ag₂Br⁺, the undissociated ion Ag₃ ^- was observed as a predominant peak in the case of Ag₃ ⁺. The dissociation behavior of Ag₂Br^* can be explained on the basis of the calculated thermochemical data. Contrary to this, the predominant existence of the undissociated Ag₃ ^- cannot be explained by the reported thermochemical data. The existence of undissociated Ag₃ ^- suggests that the dissociation barrier is higher than the internal energy of Ag₃ ^* (theoretical: 1.03 eV, experimental: 2.31 eV) estimated from the ionization potentials of Ag₃ and Cs.     

X-ray study of c-axis parameters in disordered stage II Agχ TiS2

X-ray measurements have been performed on disordered Stage II Ag_χ TiS₂ crystals with χ = 0.18 and 0.19. The c-axis structure was determined using the 00.l reflections for 4 ?l? 29. A principal result is that the intercalation of Ag⁺ between S layers produces unequal TiS distances in the adjacent TiS₂. The charge transfer to the Ti layer produces an expanded TiS distance adjacent to the Ag layer. The TiS distance away from the Ag ions is accordingly contracted. This effective (indirect) repulsive interaction between Ag⁺ and Ti may provide a mechanism for staging in these materials by keeping the Ag layers as far apart as possible.     

Electron paramagnetic resonance in Nd-Ag amorphous alloys

We have studied the EPR of Nd³⁺ ions in Nd_16.7Ag_83.3 amorphous alloys between 4.2 K and room temperature. The resonance observed above 100K at a field corresponding to a g ? 2.3 indicates the existence of sites having a non-axial crystal field of the form J²_x-J²_z.     

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.     

197Au and125Te Mössbauer spectroscopic study on the low temperature phases of Ag3AuX2 (X=S,Se, and Te)

¹⁹⁷Au and¹²⁵Te Mössbauer spectroscopy has been applied for the low-temperature β-phases of Ag₃AuX₂ (X=S, Se, and Te). The values of I. S. and Q. S. for¹⁹⁷Au suggest that the gold atoms, linearly coordinated by two chalcogen atoms in these phases, exist as monovalent cations. The¹²⁵Te Mössbauer spectra suggest that the tellurium atoms are substantially ionic for both Ag₂Te and Ag₃AuTe₂. The nature of X-Au-X bonds is discussed on the basis of the Mössbauer data and the bond distances.