On the third order elastic constants of AgCl-AgBr mixed system

Lowdin's many body effect is accounted to explain the violation of Cauchy's relation (C₁₂=C₄₄) in silver halides. Lundqvists potential model with many body effect has been used to evaluate the third order elastic constants of AgCl and AgBr. A modified Lundqvist potential model is used to calculate the third order elastic constants for the simple AgCl- AgBr mixed system with varying concentration of AgCl and AgBr.     

Localized modes of Li and Na impurities in silver halides

The absorption bands due to the infrared-active localized modes of Li and Na substitutional impurity in AgBr and of Li in AgCl are studied at 2 K. The isotope effects of the localized modes are observed in AgBr: Li and AgCl: Li systems. The high frequency sidebands of the Li⁶ localized mode in AgBr are also measured.     

Diffusion of 22Na in Cd-doped silver bromide and silver chloride

The diffusion coefficients of ²²Na tracer in zone-refined, CdBr₂-doped, polycrystalline AgBr were measured. An approach is developed to calculate the intrinsic concentration of Frenkel defects in AgBr and AgCl based on the ²²Na diffusion data. The theory is based on the usual assumptions of random walk and electroneutrality.     

EPR and optical spectra of Ni2+-VAg in silver chloride and silver bromide

The optical absorption and EPR spectra of Ni²⁺-V_Ag centres in the AgCl:Ni²⁺ and AgBr:Ni²⁺ systems have been investigated theoretically on the basis of the complete energy matrices including the electron–electron repulsion interaction, the ligand field interaction, the spin–orbit coupling interaction, and Zeeman interaction. Because the charge compensation forms a silver ion vacancy (V_Ag) which makes the attractive force acted on the each ligand ion different, it was determined that the Ni–X (X = Cl, Br) distance next to V_Ag is shorter than others for both AgCl:Ni²⁺ and AgBr:Ni²⁺ systems in the tetragonal symmetry. Besides, it was found that the local lattice structure of (NiX₆)^4? clusters in AgCl and AgBr crystals exhibit a compression distortion. This compression distortion may be ascribed to the fact that the Ni²⁺ ion has a smaller ionic radius and more effective charge than the Ag⁺ ion.     

The formation volume of Frenkel defect in silver halides

The formation volume ν_f of a (cation) Frenkel Defect is calculated in AgCl and AgBr. The proposed formula for ν_f has no adjustable parameters and contains the formation enthalpy (of a Frenkel defect), the compressibility of the solid at absolute zero and the pressure derivative of the compressibility. The calculated values are in good agreement with the experimental results.     

The elastic constants and their temperature and pressure derivatives of AgBr-AgCl mixed crystals

The three independent second-order elastic constants and their temperature and pressure derivatives have been measured for four AgBr-AgCl mixed crystals, with 19.5, 39.1, 56.6 and 78.7 mole % AgCl, using the ultrasonic pulse-echo technique at room temperature. The explicit temperature dependence of the elastic constants is calculated and is found to be much larger than that of other NaCl structure crystals. The violation of the Cauchy relation C₁₂ = C₄₄ is found to be significant and increases between AgBr and AgCl. The high temperature limit of the Gruneisen parameter is calculated from the elastic data. A comparison is made between the elastic properties of the silver halides and the alkali halides.     

Variations of chemical bonds in silver halides under high pressures

ABSTRACT

Rocksalt structured AgI (rs-AgI), which appears under pressures between 0.4 and 11.3?GPa, shows high ionic conductivity as high as that in α-AgI, especially at high temperatures. Microscopic origins of ion conduction mechanisms have not been clarified until now and are therefore investigated using the discrete variational Xα (DV-Xα) cluster method. Comparable studies for AgCl and AgBr, which are known as high ionic conductors just below melting temperatures and form the rocksalt structure, are also done. Ionic interactions between a mobile Ag ion and remaining ions are almost the same between those under different pressures, while covalent interactions between the mobile Ag ion and the remaining Ag ions change drastically when the mobile Ag ion is migrating. Similar results are also obtained for AgCl and AgBr. The covalent interactions between the mobile Ag ion and the remaining Ag ions, which should affect the Ag ion migration, play important roles in not only rs-AgI but AgBr and AgCl.     

Compare the photocatalytic properties of nanocomposites with tandem n (AgBr)-n (Ag2CO3) and p (AgCl)-n (Ag2CO3) heterojunctions

In this work, Ag₂CO₃ nanoparticles (NPs) (as a n-type semiconductor) incorporated in mordenite zeolite (MOR) by a facile precipitation method. Silver halides, AgCl (as a p-type semiconductor) and AgBr (as a n-type semiconductor), with different weight percentage (20%, 40% and 50%) were coupled into Ag₂CO₃-MOR nanocomposite (NC) and producing a series of novel AgCl/Ag₂CO₃ (p-n heterojunction)-MOR and AgBr/Ag₂CO₃ (n-n heterojunction)-MOR NCs. The effects of silver halides on the Ag₂CO₃–MOR catalyst for the photocatalytic degradation of methyl blue (MB) under visible light irradiation have been investigated. The structure, composition and optical properties of NCs were investigated by UV–Visible diffuse reflectance spectroscopy (UV–Vis DRS), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM). The prepared AgX/Ag₂CO₃-MOR NCs with the optimal content of AgX (50 wt%) indicated higher photocatalytic activity than that of the Ag₂CO₃-MOR and Ag₂CO₃. The cycle experiments on the heterojuctions NCs indicated that photocatalytic stability of AgBr/Ag₂CO₃-MOR NC was more than AgCl/Ag₂CO₃-MOR NC in all cycles. On the basis of the experimental results, a possible mechanism for the enhanced photocatalytic activity and photoinduced stability of silver compounds was proposed.     

Ionic conductivity of mixed silver halide crystals

To evaluate the effects of mixed halides on the lattice defect parameters of the silver halides, we have measured the ionic conductivity both of the entire range of mixed AgBr-AgCl single crystals, aftd also of several iodide-doped crystals. For the AgBr-AgCl system, the intrinsic conductivity at a given temperature decreases monotonically from pure AgBr to pure AgCl. The deduced Frenkel defect formation energy varies only a little from 0 to 50 mole % AgCl, and then increases rapidly with further increase in AgCl content, closely paralleling the ratio of bulk modulus to dielectric constant. The defect formation energy in these crystals hence reflects the average macroscopic properties of the solid solution. For the iodide-doped crystals, however, the results are quite different. Small amounts-of iodide cause large increases in the conductivity of AgBr andiAgCl, especially in the latter. These results suggest that the elastic strain introduced by the oversized iodide ion exerts an appreciable local effect on the Frenkel defect formation, in contrast to the crystal-averaged response found for the AgBr-AgCl solid solutions. Furthermore, the Arrhenius plots for the conductivitiei of the AgBr: I specimens show curvature which suggests a temperature-dependent pairing of the solute.     

Excitonspektren von Silberhalogeniden und ihren Mischungen

The absorption spectra of AgBr and AgCl as well as their mixtures were investigated at liquid oxygen temperature. There are two characteristical features for exciton bands: the terms of the free atoms, and the structure of the crystal lattice. For pure and mixed crystals there exist doublets which can be derived from the terms of the free halide atoms. The wavelengths of the exciton bands shift linearly with increasing content of AgCl in AgBr. For the first band of the absorption edge this shift is 70 cm^?1 per mole percent admixture. The bands shift to a greater extent than they broaden. Thus from statistical calculations can be deduced that there is a region of about 125 anions responsible for an absorption act. The exciton bands depend considerably on thermal influences from the lattice as well as on distortions resulting from ultraviolet exposure.     

Middle-infrared luminescence of praseodymium ions in silver halide crystals and fibers

The luminescence of AgBr, AgCl, and AgClBr crystals and fibers doped with Pr3+ ions was investigated in the middle-infrared spectral range. We measured the absorption, emission, and kinetic parameters over a broad temperature range. Strong luminescence in the spectral range 4-5.5 microm was observed for the first time to our knowledge in silver halide crystals and fibers at room temperature. No noticeable differences were observed between the crystals and the fibers. We calculated various optical parameters for Pr:AgBr and Pr:AgCl crystals, using the Judd-Ofelt approximation. Both the measured results and the calculated parameters indicate that these doped crystals and fibers would be good candidates for the fabrication of mid-IR solid-state lasers or fiber lasers.     

X-ray determination of the Debye-Waller factors and Debye temperatures of AgCl and AgBr

The integrated intensities of Bragg reflections are measured for AgCl and AgBr at room temperature using an x-ray powder diffractometer. The Debye-Waller factors and Debye temperatures are evaluated.     

Valence bands of silver halides determined by X-ray and UV photoemission

Photoemission from AgCl, AgBr, and AgI has been studied at photon energies hω = 16.8, 21.2, 26.9, 40.8, 48.4 and 1486.6 eV. By exploiting the strong     

Preparation of AgBr-detectors doped by some chemical elements Bi, Mn, Zn, Sn, Hg, Ca, Al, Ba, Cd and its sensitivity determination

One of the possible methods of increasing the sensitivity of track Aghal detectors by replacement of AgCl with AgBr is presented.     

A method of preparing thin sheets of AgCl and AgBr by capillarity

The paper describes a method of preparing thin sheets of AgCl and AgBr making use of capillarity. The melt is sucked up into a narrow vertical plane-parallel gap between glass slides as a result of excess pressure. After cooling to room temperature the glass slides must be separated from the sheet of AgCl (AgBr) which has been produced. The AgCl sheet has a high-quality surface. When the temperature conditions are suitable the sheet consists of large (several cm²) grains. The dependence of the quality (of the relief) of the grain surface on the crystallographic orientation was determined.In conclusion the author wishes to express his thanks to Prof. L. Zachoval for valuable advice and remarks, R. Kiradjieffová for passing on her experimental experiences and N. Kozelková for her help in the experimental work.     

甲酸根离子均匀掺杂的卤化银中的光电子特性

甲酸根离子(HCO-2)作为一种“空穴-电子转换剂”掺杂在卤化银中,可以提高潜影形成过程中光电子的利用率,俘获光生空穴,减少潜影形成过程中电子-空穴复合所造成的电子损失;同时还可以释放一个电子,提高感光效率。采用微波吸收介电谱检测技术,检测了不同浓度甲酸根离子均匀掺杂的立方体AgCl和AgBr乳剂在脉冲激光作用下所产生的光电子衰减信号。通过比较光电子的衰减时间和寿命,分析了甲酸根离子的空穴陷阱效应对立方体AgCl和AgBr乳剂中光电子衰减行为的影响,并得到了最佳均匀掺杂浓度（10^-5mol/molAg）。     

Determination of non-stoichiometry in n-type AgBr by the measurement of transient current in an improved dc polarization cell

In order to determine the non-stoichiometry in AgBr, the transient current in a dc polarization cell, Ag/AgBr/Pt, was studied. When electrolytic current in the cell was completely blocked, only electronic current was allowed to flow through the AgBr/Pt interface, whereas both ionic and electronic carriers were transported through the Ag/AgBr interface at transient state. The ionic current through the Ag/AgBr interface was related to the change in δ in the formula of Ag_1+δBr. The following methods were proposed to determine δ from the transient current measurement: (i) The chemical diffusion coefficient, D?, of AgBr was calculated from the analysis of the time change in transient current. The electronic conductivity, σ_e, of AgBr was obtained from the steady-state current according to Wagner's theory. From D? and σ_e, δ was calculated. (ii) The transient current at the Ag/AgBr interface was divided into ionic and electronic parts using D? determined in (i). By integrating the ionic current, the change in δ was calculated. Using an improved dc polarization cell, the complete ion-blocking at the AgBr/Pt interface was achieved. The transient current after the abrupt change in applied potential was measured at 400°C. The methods (i) and (ii) were applied to the analysis of transient current and δ⁰, δ of AgBr in equilibrium with silver metal, was determined to be (2.0±0.2) x 10^-6.     

The absorption spectrum of polycrystalline silver halide fibres

The wavelength dependence of the attenuation in polycrystalline AgCl:AgBr fibre has been determined between 2.5 μm and 14 μm. The background attenuation as λ^-2 dependence as expected but there are also strong absorption peaks due to water and silver oxide which, to our knowledge, are observed for the first time in these fibres.     

Charged dislocations in ionic crystals

Experiments and theories concerning charged dislocations in alkali halide crystals are reviewed in detail, with particular attention to the way in which the experiments should be interpreted and to the range of applicability of the sweep-up and various forms of thermal-equilibrium models. Possible effects on mechanical properties and internal friction are analysed. The transient and steady-state effects of plastic deformation on ionic conductivity are described and new interpretations involving charged dislocations are proposed. A survey of results on the scattering of light by alkali halide single crystals leads to the conclusion that charged dislocations do not play an important role.

Evidence about charges on surfaces and on dislocations in AgCl and AgBr is reviewed and compared with that for alkali halides. Comparisons are also made with MgO, the CsCl and CaF₂ structures, semiconductors and ice.