Diffusion Of Barium Research Articles

Tailoring Work Functions of Heterostructures by Varying the Depth of a Buried Monolayer

AbstractThe work function is a critical parameter for device design and understanding of materials properties, but contemporary experimental literature on tailored work functions is rather scarce. This paper presents a promising new approach to work function design that uses pulsed laser deposition (PLD) growth with unit cell precision. It is shown that a monolayer buried within a material can influence the work function as a function of the layer depth. This method can preserve properties of the original material's surface, and furthermore, a sensitive material can be used as the monolayer, both of which are beneficial for device design. Proof of concept is demonstrated by inserting a nominal monolayer of barium oxide (BaO) into strontium titanate (SrTiO3) (001) at different depths, revealing a previously unknown work function trend. Density functional theory (DFT) calculations, surface characterization, and scanning transmission electron microscopy (STEM) studies verify the quality of the heterostructures and help to understand how charge transfer, slight barium diffusion, and termination effects account for the observed work function trends. This work function tunability is a promising approach for future devices that require a tailored work function, which can easily be extended to a wider variety of materials.

Assessment of barium diffusion from therapeutic mud wrapped in micro-perforated polyethylene bags towards the human organism

Barium is present within the clay-derived therapeutic mud packs deposed on the patient's skin for treating some rheumatologic conditions. We studied in twenty-four young healthy volunteers the diffusion of Ba from mud wrapped in micro-perforated polyethylene bags and soaked in mineral water. No significant systematic increase in plasma or urine Ba levels was evidenced when comparing pre- and post-treatment samples using inductively-coupled plasma mass spectrometry. These levels were markedly inferior to the recommended thresholds in nearly all the participants. Noticeably variability in blood and especially urine Ba concentrations was large and mainly explained by environmental exposure (alimentation). Interestingly, we evidenced an intense Ba accumulation within the therapeutic mud at the end of the regimen. Because we chose a clay with one of the highest Ba content available in France for medical therapy and participants with an optimal transcutaneous diffusion capacity (young individuals with low-fat mass), we conclude unambiguously that there is no risk of Ba overexposure in patients receiving pelotherapy according to the procedure used in French medical spas.

EXPERIMENTAL AND MODEL EVALUATION OF DIFFUSION COEFFICIENTS OF BARIUM IN LIQUID GALLIUM AND LEAD

Gallium and lead are used as liquid cathodes to produce alloys of alkaline earth metals, including barium. Data on the diffusion coefficients of barium (DBa) in liquid metals obtained by anodic chronopotentiometry are very limited. In this paper, an experimental evaluation of DBa in liquid gallium and lead was carried out by a combined method. It is based on the joint processing of the measurement data of the cathode chronopotentiometry in the coordinates E–ln√τ and the equations of the isotherms of the potentials of the alloys of the E–lnXBa obtained under the same conditions. Measurements were carried out in the melt KCl– 26 mol % BaCl2, at temperatures from 953 to 1073 K. The basis for the calculation of DBa is the Sanda equation. The features of electrode processes on liquid metal cathodes in barium-containing chloride melts are taken into account. The values of stabilized residual current densities depending on the temperature are established. It is shown that at the beginning of the process of barium separation into alloys, the effect of joint potassium deposition is manifested, especially on the lead cathode. The contribution of barium current output is proposed to be estimated by the current selectivity index, which depends on the potential of the alloy. It is shown that the joint discharge of potassium and barium into alloys leads to an overestimation of dva on gallium and lead from 5 to 12%. The activation energies of barium diffusion in gallium and lead, respectively 20.7 and 16.2 kJ/mol, were calculated on the basis of the obtained temperature dependences of DBa. Calculations show that on liquid thallium, bismuth, antimony measurement of cathode chronopotentiograms for barium is impossible, because of significant potassium co-deposition. Based on the data on the structure of dilute alloys and thermodynamic characteristics of alkaline earth metals, the method of calculation of reduced radii of microgroups-diffusers in the Stokes – Einstein equation is proposed. The DMe values calculated using the reduced radii are in satisfactory agreement with the majority of experimental data. These facts confirm the validity of the model of collective diffusion of barium and other alkaline earth metals in alloys as part of microgroups by translational mechanism.

Mineral Precipitation in Fractures and Nanopores within Shale Imaged Using Time-Lapse X-ray Tomography

Barite precipitation in fractures and nanopores within a shale sample is analysed in situ, in 3D, and over time. Diffusion of barium and sulphate from opposite sides of the sample creates a supersaturated zone where barium sulphate crystals precipitate. Time-lapse synchrotron-based computed tomography was used to track the growth of precipitates over time, even within the shale’s matrix where the nanopores are much smaller than the resolution of the technique. We observed that the kinetics of precipitation is limited by the type and size of the confinement where crystals are growing, i.e., nanopores and fractures. This has a major impact on the ion transport at the growth front, which determines the extent of precipitation within wider fractures (fast and localised precipitation), thinner fractures (non-localised and slowing precipitation) and nanopores (precipitation spread as a front moving at an approximately constant velocity of 10 ± 3 µm/h). A general sequence of events during precipitation in rocks containing pores and fractures of different sizes is proposed and its possible implications to earth sciences and subsurface engineering, e.g., fracking and mineral sequestration, are discussed.

Surface processes at the first stage of magnetron cathode Pd-Pd5Ba activation

The electron emission of palladium-barium cathodes is highly effective due to the active BaO substance formation of low work function on the cathode surface (2.3 eV). The work function is a universal parameter characterizing the emission capacity of material. The degree of cathode surface coverage with the emission-active layer and distribution uniformity specificate such important parameters as the emission current and homogeneity of the cathode surface. The active metal – barium – is part of the activation phase – Pd5Ba intermetallic compound. The active substance layer is formed during the activation by vacuum cathode heat treatment. At thermal Pd5Ba dissociation, diffusing Ba atoms flux through the defects in the crystal structure of a palladium matrix to be oxidized by the residual oxygen locked in a device. This article is a first attempt to analyze the correlation of emission-active substance distribution over the cathode surface with the mechanisms of barium diffusion in the emitter. At the first stages of thermal activation, BaO active substance was locatized on the palladium-barium cathode surface by scanning electron microscopy (SEM) and high spatial resolution electron probe microanalysis. The analysis reveals that Ba atoms fluxing through grain boundaries form a line of the emission-active substance along the grain boundaries. The line width is in the region of several microns. In places of triple joints, BaO formations are mostly sizeable. BaO nanoparticles are formed on the surface of individual grains due to Ba diffusion through dislocation tubes. The series of vacuum cathode annealing showed that at T = 750 °C, BaO reproduction from diffusing Ba atoms does not compensate for the BaO evaporation rate. The annealing process, carried out for 30 min at T = 900 °C, has led to the active layer formation along the grain boundaries and to the formation of BaO nanoparticles on the surface of some grains. We introduce an original technique for assessing the surface coverage degree of a cathode covered with an emission-active substance. The technique implies using electronic microimages processed with the ImageMagick.

The sorption and diffusion of 133Ba in crushed and intact granitic rocks from the Olkiluoto and Grimsel in-situ test sites

The distribution coefficients of barium on Olkiluoto pegmatitic granite and veined gneiss, Grimsel granodiorite and their main minerals (quartz, plagioclase, potassium feldspar and biotite) were obtained by batch sorption experiments carried out as a function of the concentration of barium. The distribution coefficients on biotite and veined gneiss were modelled with the PHREEQC computing program. In addition, the diffusion of barium into rock cubes was also studied both experimentally and computationally and the rock cubes from the diffusion experiments were studied with autoradiography and scanning electron microscopy. The results showed that the distribution coefficients of barium were largest on biotite and the sorption as a function of barium concentration on all the minerals followed a similar trend. The distribution coefficients of barium on veined gneiss, pegmatitic granite and granodiorite followed the distribution coefficient trend of their main minerals and the distribution coefficients were largest on granodiorite due to the low salinity of the groundwater simulant. The distribution coefficients of barium on veined gneiss were of the same magnitude as on granodiorite because of the high biotite content of veined gneiss and those on pegmatitic granite were a magnitude smaller. It was also discovered that the distribution coefficients in saline water were considerably smaller than the results obtained in low salinity water, which suggests that competing ions play a significant role in the sorption of barium. Finally, the concentration decrease of barium in the solution in the diffusion experiments was largest in granodiorite which can be explained with both the porous structure of all the minerals of granodiorite leading to high accessible surface area and with the sorption properties of barium. It was discovered with autoradiography that the barium was mainly sorbed on the dark minerals of the rocks, but, additionally, barium sorption on plagioclase was also concluded to be significant. In addition, the sorbed barium could be seen with scanning electron microscopy on the biotite and calcite veins in the fissures of the rock in granodiorite and veined gneiss.

Timescales of magmatic processes prior to the ∼4.7 ka Agnano-Monte Spina eruption (Campi Flegrei caldera, Southern Italy) based on diffusion chronometry from sanidine phenocrysts

Barium diffusion chronometry applied to sanidine phenocrysts from the trachytic Agnano-Monte Spina eruption (∼4.7 ka) constrains the time between reactivation and eruption of magma batches in the Campi Flegrei caldera. Backscattered electron imaging and quantitative electron microprobe measurements on 50 sanidine phenocrysts from representative pumice samples document core-to-rim compositional zoning. We focus on compositional breaks near the crystal rims that record magma mixing processes just prior to eruption. Diffusion times were modeled at a magmatic temperature of 930 °C using profiles based on quantitative BaO point analyses, X-ray scans, and grayscale swath profiles, yielding times ≤60 years between mixing and eruption. Such short timescales are consistent with volcanological and geochronological data that indicate that at least six eruptions occurred in the Agnano-San Vito area during few centuries before the Agnano-Monte Spina eruption. Thus, the short diffusion timescales are similar to time intervals between eruptions. Therefore, the rejuvenation time of magma residing in a shallow reservoir after influx of a new magma batch that triggered the eruption, and thus pre-eruption warning times, may be as short as years to a few decades at Campi Flegrei caldera.

Preparation of highly (001)-oriented α-Fe2O3 film on Si-substrate from drop coated BaFe12O19 via barium diffusion-induced transformation

Oriented iron oxide structure is of particular importance in electronic, magnetic, and catalytic applications. We report on a facile route to prepare (001)-oriented hematite (α-Fe2O3) film on a silicon substrate with drop coated BaFe12O19 nanoplates from hydrothermal process as precursor. The obtained α-Fe2O3 film displays an ultrahigh (001) orientation of 99.4% when treated at 1300°C for 5h. Transformation of BaFe12O19 into α-Fe2O3 is driven by directional diffusion of barium into the interface between BaFe12O19 coating and the substrate, where a thermodynamically stable barium silicate was produced. Given the structural similarity between BaFe12O19 and α-Fe2O3, the crystallographic direction of BaFe12O19 [001] is topologically converted into α-Fe2O3 [001] during the transformation. The ultrahigh degree of orientation of the α-Fe2O3 film is attributed to the large aspect ratios of the starting BaFe12O19 nanoplates, which facilitate the realignment of plates, causing them to flatten on the substrate during heat treatment.

The improvement of barium-containing anode for ceria-based electrolyte with electron-blocking layer

An original approach aiming at the improvement of barium-containing anode in the reduction of partial internal electronic short circuit for ceria-based electrolyte in intermediate temperature solid oxide fuel cells (IT-SOFCs) was proposed in this research. The improved cells employed by mixed proton-oxide ion-electron conducting composite anodes show efficiently enhanced properties, especially in the effective increase of power densities. The electron-blocking layer can be maintained with a suitable proportion of Gd0.1Ce0.9O2-δ (GDC) below 20 mol% at anodes. Furthermore, a mechanism for barium diffusion and ionic conduction behavior in barium-containing anodes of the improved cells was proposed.

Formation mechanism of highly [0 0 1]c textured Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 relaxor ferroelectric ceramics with giant piezoelectricity

We investigated the synthesis mechanism and giant piezoelectricity of highly [001]c textured Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) relaxor based ferroelectric ceramics (texture fraction ∼94%) with BaTiO3 (BT) templates. The onset of texture occurred at ∼88% relative density (RD), and rapid increase in texture fraction happened with RD>94%. A PbO-rich grain boundary liquid of ∼6–13nm thickness, detected at oriented crystalline interfaces, facilitated epitaxial nucleation and subsequent [001]PIN-PMN-PT||[001]BT growth of textured grains on BT templates. Interfaces between BT templates and PIN-PMN-PT textured grains were found to be coherent and defect-free at the atomic scale, and there was almost no barium diffusion across the interfaces during the texturing process. Nanodomains were clearly visible in the oriented grains. [001]c poling ordered the domain structures of textured ceramics and resulted in a more uniform domain size of several hundred nanometers. The textured ternary PIN-PMN-PT ceramics exhibited ∼200% improvement in piezoelectric response relative to their random counterparts, as a result of their piezoelectric anisotropy and engineered domain status along with higher mobility of domain walls.

Structural analysis of thermal degradation and regeneration in blue phosphor BaMgAl10O17:Eu2+ based upon cation diffusion

Thermal degradation of blue phosphor BAM:Eu2 + under air is investigated using XPS, XRD, EPR and photoluminescence (PL) in order to analyze the loss of intensity in terms of modifications of the dopant distribution in the crystal cell and between crystal bulk and surface. This study reveals the key role played by oxidation-driven 2D diffusion of europium and barium, that results in important concentration gradients and makes degradation strongly dependent on both microstructure and cooling speed. Also based upon cation mobility, a possible regeneration effect is evidenced at moderate temperature. Flux treatments, known to increase the intensity of photoluminescence, also appear to reduce thermal degradation by lowering specific surface; they also enhance the regeneration process by forming extended single-crystal domains conducive to cation diffusion.

Analysis and Characterization of Phase Evolution of Nanosized BaTiO3 Powder Synthesized Through a Chemically Modified Sol-Gel Process

In the current research, a cost-effective and modified method with a high degree of reproducibility was proposed for the preparation of fine nanoscale and high-purity BaTiO3. In contrast to the other established methods, in this research, carbonate-free BaTiO3 nanopowders were prepared at a lower temperature and in a shorter time span. To reach an in-depth understanding of the scientific basis of the proposed process, an in-detail analysis was carried out for characterization of nanoscale BaTiO3 particles via differential thermal analysis (DTA)/thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques aided by theoretical calculations. The effects of the temperature and time of calcination process on the preparation mechanism, phase transformation, tetragonality, and particle size of BaTiO3 were examined. The reaction that results in the formation of barium titanate initiated at approximately 873 K (600 °C) and seemed to be completed at approximately 1073 K (800 °C) and the polymorphic transformation of cubic to tetragonal initiated at approximately 1173 K (900 °C). It seemed to be completed at approximately 1373 K (1100 °C). According to the reaction mechanism, the formation of BaTiO3 in the initial stage of the interfacial reaction between BaCO3 and TiO2 depends on the BaCO3 decomposition. In the second stage, the BaTiO3 formation is controlled by barium diffusion through the barium titanate layer. In this stage, in contrast to the literature, no secondary phase was detected. The overall characterizations showed the temperature is more effective than time on the progress in process of preparation because of its diffusion-controlled nature.

High temperature degradation of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ membranes in atmospheres containing concentrated carbon dioxide

Degradation of microstructure and phase composition of perovskite-structured Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ membrane was investigated after exposure to CO 2-containing atmospheres in the temperature range of 800–900 °C. A carbonate surface layer was formed on the treated membrane. Adjacent to the carbonate layer is an intermediate decomposed zone, consisting of mainly CoO and a Ba–Sr–Co–Fe oxide compound as well as (Ba, Sr)CO 3 carbonate. Three different carbonate phases were observed, depending on the annealing conditions. The growth of both the carbonate top layer and the decomposed zone obeys a parabolic rate law, indicating a diffusion-controlled growth mechanism. The growth kinetics and mechanism are insusceptible to the change of partial pressure of oxygen and carbon dioxide under the given conditions. Deviation from the nominal composition was observed in this decomposed zone, which becomes more pronounced closer to the carbonate top layer. The carbonate layer was found to grow outward, which indicates outward diffusion of barium and strontium cations under their respective chemical potential gradient. Full substitution of Co by Fe in this material leads to reduced degradation rate in CO 2, which is consistent with the lowering of the chemical potential of the A-site cations. The adverse effect of CO 2 was found to be more pronounced at the grain boundaries of the membrane.

Behavior of Ba(Co, Fe, Nb)O3-δ Perovskite in CO2-Containing Atmospheres: Degradation Mechanism and Materials Design

This study investigates the degradation behavior and mechanism of perovskite-type BaCo0.4Fe0.4Nb0.2O3-δ membranes in CO2-containing atmospheres at 800−1000 °C and examines the influence of cation substitution on the CO2 resistance. The oxygen permeation flux deteriorates rapidly upon switching the sweep gas from Ar to CO2. During exposure to CO2, the membrane material decomposes to form a compact BaCO3 surface layer and a subjacent porous decomposed zone which consists of CoO and a Co-depleted Ba(Co, Fe, Nb)O3-δ perovskite phase. Within this zone, the composition of the perovskite product varies with depth, with more pronounced cobalt depletion found closer to the carbonate layer. The growth of the product layers is found to be diffusion-controlled and can be enhanced by the presence of oxygen. Outward diffusion of barium from the unreacted perovskite bulk appears to rate limit the growth. A drop of the barium chemical potential is concurrent with a larger degree of cobalt depletion in the Ba(Co, Fe, Nb)O...

Viscosity and diffusion of barium and fluoride in Na 2O/K 2O/Al 2O 3/SiO 2/BaF 2 glasses

The interdiffusion coefficients of barium and fluoride in glasses, in the system Na 2O/K 2O/Al 2O 3/SiO 2 with BaF 2 additions, were determined from the diffusion profiles using energy dispersive X-ray analysis in a scanning electron microscope. The diffusivities were in agreement with Arrhenius-equation. Diffusion coefficients of fluoride were in the range from 4.5 × 10 −15 m 2 s −1 to 30 × 10 −15 m 2 s −1 at 580 and 640 °C, respectively, while those of barium were 0.035 × 10 −15 m 2 s −1 at 600 and 1.3 × 10 −15 m 2 s −1 at 680 °C and hence are around two orders of magnitude smaller than the values for of fluoride. During the diffusion of F −, the charge compensation is assumed to be predominantly achieved by the simultaneous diffusion of highly mobile alkali ions. The viscosity of the melts decreased with increasing BaF 2-concentration. The diffusion coefficients did not obey Stokes–Einstein Law. In the case of the crystallization of BaF 2 from silicate glasses, the rate determining step should be the diffusion of barium.

Self- and foreign alkaline-earth diffusion in mixed cation silicate glasses

Self-diffusion of alkaline-earth ions in various mixed cation silicate glasses of the composition A 2O·2MO·4SiO 2 was investigated by radiotracer diffusion measurements below the respective glass transition temperatures. Including previous measurements, we have analyzed the diffusivity of divalent ions in mixed cation systems with A = Li, Na, K, Cs and M = Ca, Sr, Ba. The activation enthalpy depends strongly on the type of cations, revealing an increasing diffusivity for glasses with cations of similar size. The behavior is consistent with mechanical loss spectroscopy measurements performed on the same glasses. In addition foreign atom diffusion of calcium and barium in strontium containing glasses were performed. In the case the ionic radius of the alkali ions exceeds that of the alkaline-earth ions the diffusion activation enthalpy of the foreign ion equals the activation enthalpy of self-diffusion. The results can be described on the basis of a theoretical model proposed by Kirchheim [R. Kirchheim, J. Non-Cryst. Solids 328 (2003) 157] that relates the activation enthalpy to electrostatic and elastic contributions.

Heavy ion Rutherford backscattering spectrometry (HIRBS) study of barium diffusion in borosilicate glass

Diffusion of barium in borosilicate glasses containing sodium and calcium has been studied using heavy ion Rutherford backscattering spectrometry (HIRBS) using 30MeV 19F beam. A thin layer (25μg/cm2) of BaCl2 was vacuum evaporated on the polished surface of the glass samples which were then annealed at different temperatures (573–723K) and subsequently subjected to HIRBS measurements. It was observed that introduction of 10mole% of calcium in place of sodium results in increase in the activation energy of diffusion of barium by about 30%. This indicates that alkaline earth ions retard the diffusion process in borosilicate glass. The results corroborate the data obtained on diffusion of sodium by radiotracer method. The results have been explained in terms of the increasing rigidity of the glass network with introduction of alkaline earth ions.

Barium diffusion in mixed cation glasses

Diffusion of barium (Ba) in mixed cation glasses of the composition xNa2O x (3 - x)BaO.4SiO2 with x = 0.0, 0.1, 0.3 and 1.0 and 0.4K2O.2.6BaO.4SiO2 was investigated by means of the radiotracer diffusion technique below the respective glass transition temperatures. In accord with our previous results of calcium (Ca) diffusion in soda-lime silicate glasses (F. Natrup et al., Phys. Chem. Chem. Phys., 2005, 7, 2279), the mobility of alkaline-earth ions increases with the alkali content in all analyzed glass systems with no decrease in the diffusion activation enthalpy, but a raise in the pre-exponential factor. A distinct dependency of the activation enthalpy of alkaline-earth ions on the type and content of the alkali ions in the glass is observed. The results provide evidence for elastic and electrostatic contributions to cation diffusion in glasses and support the formation of dissimilar cation pairs, that were derived from nuclear magnetic resonance (NMR) investigations of soda-lime silicate glasses and glasses containing sodium and barium. Finally, a striking correlation between the pre-exponential factor of alkaline-earth ion diffusion in soda-lime and potassium barium glasses is found, the origin of which remains unsolved.

Charge compensation mechanism in yttria-doped barium titanate

A commercial TiO 2-excess BaTiO 3 powder doped with Y 2O 3 has been pressureless-sintered using conventional tube furnace and CO 2-laser, and the room-temperature electrical conductivity determined. Grain-growth inhibition is found to occur at ∼0.40 mol% Y 2O 3 where the refined microstructure of an average grain size of ∼1 μm is obtained from sintering at 1215 °C. The principal charge compensation mechanism in Y 2O 3-doped BaTiO 3 depending upon temperature can be divided into three characteristic regimes. The mechanism is predominantly of the cation vacancy compensation at temperatures <1210 °C, a mixed mode at 1210–1500 °C, and the electron compensation when sintering temperature exceeds 1500 °C. Sintering using the CO 2-laser has enabled the retention of the high temperature defect equilibrium which renders the room-temperature conductivity of ∼10 −2 (Ω mm) −1 to the ceramics. The sintering of Y 2O 3-doped BaTiO 3 ceramics is improved since densification is enhanced by faster barium diffusion via the extrinsic cation vacancy and coarsening suppressed by high Y 2O 3-content due to reduced grain-boundary mobility by second-phase (Y 2Ti 2O 7) pinning.

Interface formation between metal and poly-dialkoxy-p-phenylene vinylene

In this work we address the dynamics and stability of calcium/PPV and barium/PPV interfaces during and after deposition of the metal. Diffusion of calcium and barium into ${\mathrm{OC}}_{1}{\mathrm{C}}_{10}\phantom{\rule{0.3em}{0ex}}\mathrm{PPV}$ is studied with low energy ion scattering (LEIS) and x-ray photoelectron spectroscopy (XPS). During metal deposition the diffusivity is found to be orders of magnitude higher than after deposition and the diffusion coefficient was found to be dependent on the metal concentration in the PPV. Furthermore, the amount of metal inside the polymer films was found to depend on the deposition rate. These observations were explained in a two-stage diffusion model. In the first stage atoms land on the surface and diffuse fast into the polymer and in the second stage metal ionizes and is trapped and diffusion is strongly decreased. The diffusion coefficient of barium into PPV at $T=298\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is found to be almost an order of magnitude lower than the diffusion coefficient of calcium into PPV [$(0.35\ifmmode\pm\else\textpm\fi{}0.05)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}23}{\mathrm{m}}^{2}∕\mathrm{s}$ and $(2.7\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}23}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{2}∕\mathrm{s}$, respectively]. Furthermore, the activation energy of the diffusion process of barium into PPV $(0.75\ifmmode\pm\else\textpm\fi{}0.07\mathrm{eV})$ is significantly higher than the activation energy of the diffusion process of calcium into PPV $(0.62\ifmmode\pm\else\textpm\fi{}0.05\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$. The difference in diffusion coefficient and activation energy between calcium and barium are discussed in terms of an Arrhenius law of diffusion. Finally, polymer LED performance was studied as a function of the amount of metal diffused into the polymer layer. It was observed that the light output and the efficiency decreased as the amount of metal in the PPV increased. This indicates that the metal ions form charge carrier traps and exciton quenching sites in the PPV.