Diffusion Coefficient Of Iodine Research Articles

Electronic structures and molecular dynamics of gadolinium-doped FAPbI3 perovskite crystals

The additive effect of a gadolinium ion into a formamidinium lead iodide (FAPbI3) perovskite crystal on electronic structures and molecular dynamics was investigated for improving photovoltaic performance with stability. The electronic structures, band structure, partial density of state, and molecular dynamics were determined by first-principles calculation. The band distribution and charge transfer between the 5d orbital of the gadolinium atom, the 5p orbital of the iodine atom, and the 6p orbital of the lead atom promoted the carrier generation and diffusion related to short-circuit current density. The enthalpy and kinetic energy prompted stabilization of the gadolinium-doped crystal with a slight distortion of coordination structure, as compared with the decomposition of the FAPbI3 crystal. Diffusion coefficients of iodine and lead ions in the FAPbI3 crystal with defect were increased, predicting decomposition. The gadolinium-doped FAPbI3 perovskite crystal has great potential for applications in photovoltaic devices by improving photovoltaic performance.

Characterization of Dopant Diffusion within Semiconducting Polymer and Small-Molecule Films Using Infrared-Active Vibrational Modes and Attenuated Total Reflectance Infrared Spectroscopy

Understanding dopant diffusion within organic and polymeric semiconductors is of great importance toward the development of organic photovoltaic and electronic devices, many of which require layered structures with controlled doping profiles (e.g., p-n and p-i-n structures). The current paper demonstrates a new method to determine the diffusion and permeability coefficients for dopant diffusion within polymeric and small-molecule organic semiconductors using attenuated total reflectance infrared (ATR-IR) spectroscopy and taking advantage of the intense IR-active vibrational bands created when dopants such as iodine accept charge from a semiconducting polymer to generate polaronic species. The diffusion and permeability coefficients for iodine within poly(3-hexylthiophene) (P3HT) are determined to be 2.5×10(-11)±1.2×10(-11) cm2/s and 2.4×10(-8)±1.2×10(-8) cm2/s·atm, respectively. The approach is applied to P3HT/PCBM (1:1 mass ratio) films, and the diffusion and permeability coefficients through these composite films are determined to be 7.8×10(-11)±2.8×10(-11) cm2/s and 4.8×10(-8)±1.3×10(-8) cm2/s·atm, respectively. Finally, the approach is extended to determining iodine diffusion within the polycrystalline semiconductor tetraphenylporphyrin (TPP) in a bilayer film with P3HT, and the diffusion coefficient of iodine through TPP is determined to be 7.1×10(-14)±1.1×10(-14) cm2/s. Although the current paper determines diffusion and permeability for the dopant iodine, this approach should be applicable to a wide array of dopants and polymeric and small-molecule semiconductors of interest in photovoltaic and electronic applications.

Iodine Volume Diffusion Measurements in Uranium Dioxide

The presence of iodine in UO2 has a great impact on nuclear fuel behaviour, both during-in reactor operation or under long-term repository conditions. Here the volume diffusion coefficient of iodine is studied using a methodology which involves ion implantation, annealing under different oxygen potentials and SIMS (Secondary Ion Mass Spectroscopy) for the concentration profile characterization of samples. The changes in the initial concentration profile induced by annealing are interpreted using Ficks second law to determine the diffusion coefficient. The first part of this paper is devoted to the description of the applied methodology. The iodine diffusion coefficients in the bulk are shown to depend upon the annealing temperature and oxygen potential. In smaller grained polycrystalline samples, the SIMS signal is averaged out over several grains and therefore, the analysis of the depth profile changes in samples due to annealing may be efficiently compared to depth profiles in as-implanted samples. By contrast, in Cr-doped UO2 samples in which the grain size is larger than the zone analysed by SIMS, a particular methodology has to be developed. To this end, large grained material was examined using EBSD (Electron Back Scattering Diffraction) in order to determine the relative crystalline orientations of the grains. Following iodine implantations, various grains with different orientations were studied using SIMS. An attempt is presented at correlating the different sputtering rates with the various grain orientations.

Transport properties of iodine and tellurium in a thoria-2 mol% urania matrix

Diffusion properties of the volatile fission products iodine and tellurium inside the thoria based fuel matrix (ThO 2-2 mol% UO 2) were obtained by studying the release kinetics of the species from trace-irradiated fuel samples at different temperatures (1290–1790 K) in post-irradiation annealing experiments. Analysis of the kinetic data shows that the release through bulk diffusion is too low to be measurable below 1273 K. The apparent bulk diffusion coefficients for the two volatile species could be evaluated at higher temperatures in a well-defined powder sample (37–45 μm particle size, 24 m 2 kg −1 BET surface area) of the high-density fuel (>95% T.D.). Temperature dependences of the diffusion coefficients of iodine and tellurium derived from this study could be expressed in the form of Arrhenius equations as logD ′ I ( s −1)=−(15 000±1000)/T−1.19±0.63 , and, logD ′ Te ( s −1)=−(25 600±1200)/T+6.14±0.77 . Activation energies and frequency factors for diffusion of the two species as obtained from the Arrhenius equations are 286 kJ mol −1 and 6.4 × 10 −2 s −1 for I and 491 kJ mol −1 and 1.38 × 10 6 s −1 for Te. The two sets of kinetic data are quite different and they suggest that the two species have different mechanisms of their transport in the fuel matrix. The results were compared with reported data in pure urania and thoria matrices.

Migration behaviour of iodine in nuclear fuel

A novel out-reactor method has been further developed for investigating the migration behaviour of fission products in UO 2 nuclear fuel, which allows the effects of thermal diffusion, radiation damage and local segregation to be independently assessed. Tailored concentration profiles of any desired species are first created in the near-surface region of polished samples by ion implantation. The impact of either thermal annealing or simulated fission is then precisely determined by depth profiling with high-performance secondary ion mass spectrometry (SIMS). Comparison of iodine migration in UO 2 wafers that had been ion-implanted to fluences spanning five orders of magnitude has revealed subtle radiation-damage effects and a pronounced concentration dependence for thermal diffusion. At concentrations above ∼ 10 16 atoms/cm 3 much of the iodine became trapped, likely in microscopic bubbles. True thermal diffusion coefficients for iodine in polycrystalline UO 2 have been derived by modelling the low-fluence data.

Kinetics of decomposition of the solid electrolyte RbCu4Cl3I2

The processes of electrochemical decomposition of the solid electrolyte RbCu4Cl3I2 at the vitreous carbon electrode and chemical decomposition of RbCu4Cl3I2 by iodine has been investigated. The anodic decomposition of the electrolyte occurs in two steps. At first, the oxidizing electrode reaction of Cu+ ions up to Cu2+ ions takes place at potentials higher than 0.57 V and onto the electrode surface the layer of decomposition products is formed, including the compound of divalent copper RbCuCl3. Then the oxidizing reaction of I ions occurs at potentials higher than approximately 0.67 V with deposition of the iodine layer onto the electrode surface. The deposition rate of the layers of decomposition products is controlled by instantaneous nucleation and two-dimensional growth of the deposit. It was shown that slow diffusion of the iodine in the reaction product layer is a limiting step in the chemical interaction of iodine with RbCu4Cl3I2. For the compressed RbCu4Cl3I2 sample investigated, iodine diffusion coefficient was calculated to be 6.2×10−7 cm2 s−1. Iodine loss from the glassy carbon surface is about 1.1×10−4 g cm−2 s−1 at the thickness of the RbCu4Cl3I2 sample is equal to 2 mm.

Kinetics of chemical decomposition of the solid electrolyte RbCu 4Cl 3I 2 by iodine

In the solid electrolyte cell, copper–RbCu 4Cl 3I 2–I 2, glassy carbon, the EMF values at open circuit were measured as a function of time. Iodine was generated through anodic electrochemical decomposition of the electrolyte RbCu 4Cl 3I 2 and this iodine then further reacted with the fresh electrolyte. An equation was deduced which relates the EMF values to the iodine concentration at the glassy carbon surface. It was shown that slow diffusion of the iodine in the reaction product layer is a limiting step in the chemical interaction of iodine with RbCu 4Cl 3I 2. For the compressed RbCu 4Cl 3I 2 sample investigated, the iodine diffusion coefficient was calculated to be 6.2×10 −7 cm 2/s. Iodine loss from the glassy carbon surface was about 1.1×10 −4 g/cm 2 s. The thickness of the RbCu 4Cl 3I 2 sample was equal to 2 mm.

Diffusion study of implanted iodine in zirconium using ion beams

This study is related to the back end of the nuclear fuel cycle. During nuclear reactor operation, the inner side of the zircaloy cladding tube is implanted by recoil with fission products. Among them, 129I poses a real problem firstly, because it is a volatile element and secondly because it has a very long half-life ( T=1.59×10 7 years). The aim of this paper is to make an analysis of iodine diffusion into zirconium compared to zirconium oxide. In order to analyse the mechanisms involved in iodine migration, stable ( 127I) and radioactive iodine ( 131I) species were implanted into zirconium. Diffusion profiles of iodine were followed as a function of successive annealing times (up to several hours) and temperatures (in the range 400–600°C), either by using Rutherford backscattering spectrometry to profile 127I or by γ spectroscopy to measure 131I release. These two techniques allowed us to determine very low iodine diffusion coefficient values (down to 10 −17 cm 2 s −1) and to extrapolate them to waste storage conditions.

Retention of iodine in yttria stabilized zirconia

The diffusion behavior of iodine in yttria stabilized zirconia (YSZ) was investigated as a function of the temperature. Iodine implantation was performed in this cubic solid solution by irradiating material samples with 1 MeV iodine ions. The distribution of iodine was evaluated by using TRIM computer calculation and measured by Rutherford backscattering spectrometry (RBS) using 5 MeV 4He particle. The iodine profile was quantified after successive temperature steps. At each step the maximum temperature was held for 2 h. It was found, that the iodine profile remained unchanged up to 1373 K. At 1573 K iodine diffused significantly. The iodine profile was measurable up to 1773 K. Even at this high temperature a significant iodine retention is observed. The diffusion coefficient of iodine (3.5 ± 1.4 × 10 −15 cm 2 s −1) is of the same order as the temperature extrapolated data of iodine in monoclinic/tetragonal zirconia.

Diffusion Coefficients of Molecular Iodine in Aqueous Solutions

The diffusion coefficients of iodine in 0.075 mol dm-3 sulfuric acid have been determined between 298 K and 358 K, by measuring the limiting reduction currents at a platinum rotating disk electrode. A Stokes−Einstein relation is verified over the range of temperature studied. The experimental value obtained at 298 K is compared with some available relations for the estimation of diffusion coefficients at infinite dilution. The agreement is good.

Binary gaseous diffusion coefficients for iodine in helium and in argon

The binary gaseous diffusion coefficients at 1 atm of pressure for the systems iodine+helium and iodine +argon have been determined from 301 to 445 K using the modified entrainment method. The results are discussed in terms of the Lennard-Jones and Maitland-Smith intermolecular potentials

Determination of the diffusion coefficients of iodine in porphyrin thin films by utilization of the battery effect in Schottky barrier devices

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDetermination of the diffusion coefficients of iodine in porphyrin thin films by utilization of the battery effect in Schottky barrier devicesW. Andrew. NevinCite this: Anal. Chem. 1991, 63, 21, 2414–2417Publication Date (Print):November 1, 1991Publication History Published online1 May 2002Published inissue 1 November 1991https://doi.org/10.1021/ac00021a006RIGHTS & PERMISSIONSArticle Views138Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (466 KB) Get e-Alerts Get e-Alerts

Photovoltaic properties of iodine-doped magnesium tetraphenylporphyrin sandwich cells. Optimization of doping, and dark electrical properties

By fabricating, doping, and testing sandwich cells of the structure Al/Al2O3 /magnesium tetraphenylporphyrin (MgTPP)/Au under high vacuum, without contact with the atmosphere, the effect of iodine doping on the dark and photovoltaic response has been determined. The properties were found to be extremely sensitive to small variations in iodine concentration, and a method of doping was developed to give highly reproducible devices with optimum photovoltaic efficiency for this system. The doped device behaves as a metal-insulator-semiconductor structure in which a depletion layer of thickness ∼100 nm and carrier concentration ∼1016 cm3 is formed in the porphyrin near the Al-Al2O3/MgTPP interface. From analysis of the time dependence of the electrical properties after doping, a value of 1×10−15 cm2/s is obtained for the diffusion coefficient of iodine in the MgTPP film. Rectification of the dark characteristics is observed only for optimized devices, with a rectification ratio of 240 obtained for a cell having a 200-nm-thick porphyrin layer. Current transport at moderate field strengths appears to be space-charge limited in the presence of a discrete trapping level in the porphyrin, enhanced at higher fields by Poole–Frenkel emission in the oxide layer.

Rutherford backscattering spectrometry studies of iodine diffusion in polyimide

AbstractRutherford backscattering spectrometry with a 2.1‐meV He2+ion beam is used to measure the diffusion of iodine into polyamic acid and polyimide films. The iodine diffusion coefficient D decreases from its initial value of about 2X10−13cm2/s in polyamic acid to approximately 1.4 × 10−15cm2/s in partially cured polyimide, but then increases to a value of nearly 1.5 × 10−14 cm2/s in fully cured polyimide. This dramatic increase in D cannot be attributed to the “in‐plane” biaxial orientation of the polyimide molecules since indential D's were found with isotropic specimens. Microvoids less than 2 nm in size caused by water and carbon dioxide formation during imidization may, however, give rise to the observed behavior. The results demonstrate that Rutherford backscattering spectrometry with its excellent depth resolution (better than 30 nm) and good sensitivity (50 ppm iodine can be detected) is very useful for measuring the diffusion of slowly diffusing species in glassy polymers.

Adsorption Mechanism of Iodine on Activated Carbon

Abstract The characteristics and mechanisms for the adsorption of iodine from aqueous solutions or from organic solvents on activated carbon were studied. Most adsorption terminated in 24 h, but a very slow adsorption was observed even after 2 d for aqueous solutions. It was found that the adsorbed species could be quantitatively predicted using the Freundlich equation, and that Traube's rule holds for the experimental results of the adsorption equilibria from aqueous solutions and from all organic solutions except alcohols. The intraparticle diffusion coefficients of iodine in organic solvents were determined according to the Boyd equation from the experimental adsorption rate results and correlated to the viscosity of organic solvents.

Investigation of the electrical conductivity of the iodine‐polyphenylacetylene charge‐transfer complex

AbstractThe electrical conductivity of the charge transfer complex between iodine and polyphenylacetylene (PPA) has been studied. The room temperature d‐c conductivity (σ) increased by seven orders of magnitude with iodine addition, reaching a maximum of 10−5 Ω−1 · cm−1 for a 1:1 ratio of iodine to repeating unit, and its concentration dependence could be described by: σ = σ0 exp [γc(1–c) – γ/4], where c is the mole fraction of iodine. Both crystalline and amorphous cis‐PPA followed this form, the crystalline polymer having a lower conductivity at low iodine levels, but attaining the same maximum value. The trans‐polymer iodinated much less readily than cis‐PPA. Molecular weight variations did not influence iodine uptake or conductivity in the range studied. It was possible to remove virtually all iodine from the charge‐transfer complex in dynamic vacuum, and an iodine diffusion coefficient of D ≈ 10−11 cm2.s−1 was determined from the rate of weight loss. Passage of current resulted in the evolution of iodine and iodine compounds at the anode. The experiment is consistent with a predominantly ionic conduction mechanism, in which the strong concentration dependence of σ is associated with a concentration‐dependent activation energy for ionic charge‐carrier formation.

Surface Diffusion Coefficient of Iodine in Some Superionic Solid Films

Iodine surface diffusion coefficient in some Ag + ion based superionic solid films has been measured by observing the radial movement of iodine under a metallurgical microscope. The values of surface diffusion coefficient for Ag 7 I 4 PO 4 , NH 4 Ag 4 I 5 and [(CH 3 ) 4 N] 2 Ag 13 I 15 are 2×10 -8 cm 2 /sec, 6.3×10 -8 cm 2 /sec and 7.8×10 -6 cm 2 /sec, respectively at 25°C. The low value of iodine diffusion coefficient for Ag 7 I 4 PO 4 , makes it a good material for film solid state battery.

The characteristics of fission gas release from uranium dioxide during irradiation

Release rates for the unstable rare gases 88Kr, 87Kr, 85mKr, 133Xe, 135Xe, 138Xe were measured for samples of polycrystalline and large-grained uranium dioxide in the temperature range 700–1550°C. Interpretation is in terms of simple diffusion of gas atoms and their halogen precursors. Derived diffusion coefficients for iodine are compared with those obtained from direct measurements of 133I, 131I release from the same experiment and show good agreement. Diffusion coefficients calculated for krypton, xenon and iodine are similar in their magnitudes and temperature dependences, but magnitudes for bromine are much (≈ 200 times) higher.

Activation enthalpy of diffusion for iodine in mixed solvents

The diffusion coefficients of iodine diluted in two different binary mixed solvents have been measured as a function of temperature. The enthalpy of activation of diffusion was evaluated from the Arrhenius plot of the data in cyclohexane + ethanol and +iso-octane solutions. The enthalpy value for iodine in an equimolar mixture of cyclohexane + ethanol was found to be ∼1 kcal mol–1 larger than that for iodine in the two pure solvents.

The impedance of the Pt/Ag4RbI5 and C/Ag4RbI5 interphases at anodic potentials

Impedance measurements have been made on the Pt/Ag4RbI5 and C/Ag4RbI5 interphases. Rate constants for the electrochemical oxidation of I− to I2 on Pt have been determined. Steady-state measurements have enabled calculation of the solubility and diffusion coefficient of iodine in Ag4RbI5. The variation of these characteristics with pressure and particle size of electrolyte has also been investigated. The results are in agreement with those obtained from transient measurements.