AgCl Crystals Research Articles

Pressure dependence of thermodynamic properties of NaBr, NaI and AgCl

Various state-equations, derived by expanding energy as a function of volume in Taylor series and using different order Pade’s approximants, have been combined with quasi-harmonic approximation for free energy to reproduce the pressure dependence of thermodynamic properties of NaBr, NaI and AgCl crystals. We have used these state-equations to compute the reduced volume, the isothermal bulk modulus and the pressure derivative of isothermal bulk modulus for the three crystals at various pressures (up to 80 kbar) and at room temperature (T=298 K). The results obtained are reasonably good lending support to the state-equations and the technique used to extend their applicability. The significant results obtained in the present study include the unified reduced equation of state for the three crystals which generates almost a single curve for theP – V behaviour at room temperature.

Mechanism of halide conversion process of colloidal AgCl microcrystals by Br − ions : I. Observation of the dynamic changes in shape, structure, and composition

The mechanism of the halide conversion process in suspension of AgCl microcrystals by bromide ions was studied by electron microscopy, X-ray diffractometry, and electron-beam diffractometry. The typical conversion process after the introduction of Br − was found to consist of more than three distinctive steps. The first step was an almost instantaneous reaction within a few seconds for a surface conversion without apparent morphological change of the original particles. The second step was a very rapid epitaxial growth process of virtually pure AgBr crystals on every corner and partly on the edges of the AgCl cubic microcrystals with dissolution of their own {100} faces, which was finished in about 1 min at 25°C. The third step was a much slower process of about 2 h at 25°C (ca. 5 min at 45°C) for the formation of an AgCl 0.5Br 0.5 solid solution developing from the joints of AgBr guest and AgCl host by simultaneous dissolution of the guests and the hosts. After the complete dissolution of the AgBr guests, a further recrystallization process that formed a solid solution richer in chloride content followed. Finally, the conversion virtually stopped midway to yield double-structured particles of Ag(Cl, Br) shell/AgCl core. However, when the initial molar ratio of [Br −] 0 [AgCl] 0 was so high as to exceed unity, the original AgCl particles were totally decomposed into about eightfold AgBr particles in number. In this case the steps later than the second one were missing. Also, it was suggested from the subsidiary study on open systems, where bromide ions were added continuously, that the kinetics was basically controlled by the deposition rate of the solute of the AgBr component of the growing parts, though it was switched to being limited by the dissolution rate of the host AgCl crystals when their open surface area for dissolution was extremely diminished.

Ageing of AgCl/Cd nuclear track detectors monitored by luminescence spectroscopy

Abstract Solid-state nuclear track detectors, made of Cd doped AgCl crystals, are commonly prepared by rolling into the form of thin foils. Subsequent long-term relaxation is however needed to obtain good quality tracks. The present communication shows for the first time that this detector “ageing” is reflected in lowtemperature (77 K) luminescence spectra. Maximum of the emission band shows a slow (lasting for ∼ 100 hours) blue shift, the magnitude of which (as much as 25 nm) depends on the compression ratio caused by the rolling. The shift is believed to be due to the rearrangement of Cd++ ions around freshly introduced dislocations. This finding opens the possibility of monitoring non-destructively the process of detector ageing and to determine the minimum time required for saturation.

In SITU HREM study of electron irradiation effects in AgCl microcrystals

Abstract Cubic silver chloride microcrystals (size between 10 and 50 nm) were investigated with high-resolution electron microscopy. The print-out effect that occurs due to reaction with the electron beam was used to investigate the orientational relationship between the AgCl crystal and the Ag particles that are formed on the AgCl crystal. The particles are found to retain the same cubic directions as the AgCl crystal with a macroscopic form of a truncated octahedron.

Mass transfer to microparticles in agitated systems

Mass transfer to microparticles in agitated vessels was measured experimentally to establish both the turbulent and the asymptotic molecular diffusion contributions. Prior studies specifically focused on transport to microparticles, defined as those whose size is comparable to or smaller than the Kolmogoroff minimum eddy size, are limited. Further, in some cases, the earlier work that a value for the Sherwood number of less than 2 could be obtained. The asymptotic molecular diffusion contribution was experimentally measured from dissolution of 1.3- and 4-μm AgCl crystals in aqueous KCl solutions, and the exchange of Ag + ions with 9-μm ion exchange particles. These results represent the first systematic experimental confirmation that the theoretical limit of Sherwood number=2 is valid for spherical particles suspended in stirred tanks. The turbulent contribution was determined from measurements of the transfer rate to ion exchange particles, 6 to 420 μm in diameter, in aqueous glycerol solutions. The mass transfer coefficient for microparticles can be well correlated by the expression ▪ where Re = (ε d 4/gs 3) 1 3 . The turbulent contribution is compatible with a boundary layer model whose origin is in decaying microeddies. This equation also correlates well the reliable results on microparticles which could be found in the literature. A comparison of the proposed equation for microparticles with previous correlations for macroparticles, extrapolated into the microparticle regime, suggests that the use of macroparticle correlations for microparticles could significantly underestimate the turbulent contribution to mass transfer.

Analysis of compression for cuprous, silver and thallous halides

An analysis of compression, i.e., pressure-volume relationship is presented for CuCl, CuBr, CuI, AgCl, AgBr, AgI, TlCl, TlBr and TlI crystals. An interionic potential model using Harrison's repulsive interaction has been developed for calculating the pressures corresponding to different compression values. The results obtained are found to present close agreement with available experimental data on the equation of state for the crystals under investigation. It is concluded that thallous halides are more compressible as compared to cuprous and silver halides.

Highly Ion-selective and Super Ion-conductive Solid Electrolyte Thin Films of AgCl Supported in a Porous Glass

Abstract A solid electrolyte thin film of AgCl was prepared in a porous silica plate by supplying silver nitrate and sodium chloride aqueous solutions to the opposite faces of the porous plate. The film showed an extremely selective conductivity of silver ion, greater than that in AgCl crystal by seven orders of magnitude.

Cyclotron resonance of polarons in pure AgCl

An experiment of the cyclotron resonance of photoelectrons in pure AgCl crystals was performed at 6–30 K using the standard spectrometer at 35 GHz. Effective cooling of the electron temperature can be realized through heating of the lattice temperature to 22 K because of the change of electron distributions. A possible explanation is due to a process via shallow trapping states which can be assigned to D − states in this material. Newly observed resonance phenomena of electrons give a more reliable value of the effective mass of m ∗ = (0.41 ± 0.01)m e near the bottom of the polaron band in AgCl.

Temperature dependence of development of slip bands and of strain hardening in AgCl crystals

The dependence of the flow stress and the slip band density on the plastic strain has been measured at 201 K, 293 K and 363 K. The growth of deformation concentrated in an average slip band has been stated. The types of obstacles acting against the rise and development of a slip band and the temperature dependence of the strain hardening in AgCl crystals are discussed. An equation stating the dependence of the flow stress on the slip band density is presented. The hardening in AgCl crystals is classified as the stage III — hardening.

Shifting of the slip mode transition temperature range of AgCl crystals doped with NaCl to higher temperatures

The slip mode transition temperature range of AgCl crystals doped with 1·24 mol.% of NaCl is shifted to higher temperatures (compared with the transition range of relatively pure AgCl crystals), i.e. from the values of approximately 110–130 K to the values of approximately 145–165 K.

Sulfur Sensitization of Large Crystals of AgCl Doped with Sulfur in the Melt

Sulfur Sensitization of Large Crystals of AgCl Doped with Sulfur in the Melt

Adsorption of cyanine dyes on AgCl crystals studied by XPS

Adsorption of 3,3'-dimethyl-9-ethylthiacarbocyanine dyes with iodide or bromide counter ions showed two energy states of sulfur in the dye molecule, one is the adsorption state to AgCl substrate and the other occurs when dye molecules aggregated. Though iodide conversion occurred on KI adsorption on AgCl, the counter ion of the dye molecule did not cause halide conversion on adsorption. The counter ion was observed only after the first dye monolayer on AgCl was completed, and increased parallel with adsorbed dye amounts. On Ag-deposited quartz plate monolayer formation occurred only by dye adsorption compared by its counter ion, while only iodine adsorbed in KI adsorption.

Adsorption of cyanine dyes on AgCl crystals studied by XPS

Adsorption of cyanine dyes on AgCl crystals studied by XPS

Formation of wavy slip bands in AgCl crystals at low temperatures

In the temperature range of approximately 110–130 K the transition of the planar slip to the wavy one occurs in AgCl crystals. The transition manifests itself by substantial shortening of originally long and straight slip traces on the top oriented surface of the samples. The wavy slip bands (in the bulk of the sample) are created by mutual association of the narrow, straight and long slip strips.

Infrared polycrystalline waveguides made of silver halides

Single crystals of AgCl and AgBr and of their solid solution KRS-13 were grown. The lowest absorption was exhibited by the solid solution: it amounted to 6×10−5cm−1 at 10.6μ and 1.4×10−4cm−1 at 5–6μ. An investigation of the edges of many-phonon absorption yielded estimates of the minimum intrinsic optical losses, which were 10−1–10−2 dB/km at wavelengths in the range 5–10μ. Extrusion was used in the preparation of polycrystalline fiber waveguides from AgCl, AgBr, and KRS-13. The optical losses at 10.6μ in the waveguides made of AgCl (0.5 dB/m) and in KRS-13 (1.3 kB/m) were governed by the absorption, whereas in the AgBr waveguide (3.5 dB/m) they were governed by the scattering. A polycrystalline KRS-13 waveguide was prepared for the first time and it exhibited a high breaking strength (~150 MPa and a low minimum radius of elastic bending (~5 cm).

Ligand hyperfine spectra of Cu2+ in AgCl.

Electron-paramagnetic-resonance studies of crystals of AgCl doped with ${\mathrm{Cu}}^{2+}$ show a rich hyperfine structure. The hyperfine structure is a sum of the hyperfine interaction from the Cu nucleus and the superhyperfine interaction with the four Cl ligand nuclei in the plane perpendicular to the z axis of the crystal. The superhyperfine constants arising from the wave function transferred to the ${\mathrm{Cu}}^{2+}$(3${d}^{9}$) hole, through the bonding with the Cl ions in the lattice, are found to be A=20 gauss, and B=3 gauss.

Electron Spin Resonance Study of Ni2+ Centers in AgCl(Cu, Ni)

AbstractSingle AgCl crystals doped with Cu2+ and Ni2+ were studied by means of electron spin resonance. As grown crystals contain three different Ni2+ centers which reduce to Ni+ defects under illumination at 50 K with blue light. Six Ni+ defects were found with tetragonal, orthorhombic, and cubic symmetry. At 101 K the orthorhombic centers transform to the tetragonal defects. The latter become thermally unstable at 135 K and induce the decay of the Cu2+ centers.

Optically Detected Magnetic Resonance of Trapped Excitons (AgCl6)5-and (AgBrCl5)5-in AgCl Crystals

The intensities of the ODMR spectra of the STE (AgCl 6 ) 5- , and (AgBrCl 5 ) 5- in AgCl crystals are studied as functions of the microwave modulation frequencies at 1.6 K. The STE shows a broad maximum near 50∼200 Hz, suggesting the existence of polarized STE's. The intensity of the (AgBrCl 5 ) 5- becomes maximal at 300 Hz, a higher frequency than those for the STE. Though the intermediate Jahn-Teller effect of (AgBrCl 5 ) 5- is not conclusive from experiments using the circularly-polarized-light detection, analysis of the intensities of the ODMR lines indicates that the reorientation of the Jahn-Teller axis occurs frequently during the lifetime.

Dynamic Jahn-Teller Effect in the ODMR Spectrum of the Self-Trapped Exciton in AgCl Crystals

An isotropic ODMR line other than the ODMR spectra of the self-trapped exciton (STE) with the tetragonal symmetry in AgCl at 4.2 K was observed using X-band and K-band spectrometers. The g value satisfied the relation of g =( g // +2 g ⊥ )/3 where g // and g ⊥ are the g values of the parallel and perpendicular spectra of the STE. The isotropic line is ascribed to motional narrowing of the tetragonal spectra of the STE. This observation of thermal dynamic Jahn-Teller effect of the STE at 4.2 K indicates that the bound electron in the STE lowers the barrier height between three configurations of the static Jahn-Teller distortion of the self-trapped hole (STH).

ODMR of Self-Trapped Excitons in AgCl Crystals: Analysis of Polarization and Intensity of ODMR

A phenomenological theory of the radiative decay of the self-trapped excitons (STE) in AgCl crystals at low temperatures is developed. The radiative decay of magnetic sublevels of the triplet STE is determined by singlet odd wave functions admixed into the lowest triplet wave functions by spin-orbit interaction and lattice vibrations. At 4.2 K, the transition probabilities between the triplet and the singlet states of the STE through the direct process of the spin-lattice relaxation turn out to be much larger than the corresponding probabilities between the sublevels of the triplet. The theory explains satisfactorily the ODMR signals observed at 4.2 K with the assumption of negative sign of zero-field splitting, D . Discrepancies found for signals of the STE at 1.6 K are discussed in terms of the polarization of the STE produced by the neighboring electron center.