Diffusion Of Ce Research Articles

First-principles investigation of lanthanides diffusion in HCP zirconium via vacancy-mediated transport

The diffusion of lanthanide fission products plays an important role in the growth of the fuel-cladding chemical interaction (FCCI) region in metallic fuels. The use of a Zr interdiffusion barrier may mitigate the transport of lanthanides from the fuel to the cladding, but the efficacy of such a liner is not yet known. In this paper, the stability and vacancy-mediated diffusion of La, Ce, Pr, and Nd in hexagonal close-packed (HCP) Zr is investigated via density functional theory (DFT) calculations and self-consistent mean field (SCMF) analysis. DFT is used to calculate the formation, binding, and migration energies of vacancies and vacancy-solute pairs. The DFT energetics are used in the KineCluE code to calculate the Onsager transport coefficients. La is found to be the fastest diffusing species in HCP Zr and experiences an almost isotropic diffusion behavior. The other three species (Ce, Pr, and Nd) demonstrate anisotropic diffusion where the diffusion in the basal planes is significantly faster than that along the c-axis. The calculated lanthanide diffusivities in HCP Zr are fitted to an Arrhenius relation and the activation energies and prefactors are reported for the first time. Furthermore, the vacancy drag and the segregation tendencies were analyzed using the calculated off-diagonal transport coefficients. According to our vacancy-mediated diffusion model, lanthanides are expected to be enriched at vacancy sinks at low temperatures, while at high temperatures, lanthanides are depleted at sinks and will preferably diffuse into the bulk. The enrichment/depletion transition temperature depends on the diffusion direction (basal or axial) and hence will be controlled by the grain texture and orientation.

(Invited) Boosting Solid Oxide Fuel Cell Performance through the Effect of of Interstitial Oxide Ion Supplying of Oxygen Storage Capacitance Materials at Cathodic Functional Layer

Chemical compatibility between the hierachical interface components in solid oxide fuel cells (SOFCs) is an emerging critical issues that significantly impact the durability of SOFCs. However, there are several challenging issues to be solved: cost-effective manufacturing configuration, lowering the operating temperature, and durability. The creation of novel materials or long-lasting electrode/electrolyte interfaces that permit high activity (oxygen reduction or fuel oxidation) while maintaining long-term stability is one of the major barriers to the commercialization of the SOFC Rare-earth doped ceria (REDC) is commonly used to enhance durability and activity in solid oxide cells (SOCs) engineering, with Gd-doped ceria (GDC) being a popular choice for interlayer and additives in solid oxide fuel cells (SOFCs). However, the Ce diffusion into the lattice of ZrO2of YSZ-based electrolyte as a solid solution at high-temperature manufacturing still is remained to be solved. In this study, we conducted La-doped CeO2 (LDC), whose Ce-sites are highly occupied with La to avoid a solid solution of Ce-Zr, as a functionalized interlayer between YSZ-based electrolyte and cathode. When LDC (La-doped CeO2, LDC, Ce0.6La0.4O2−δ) or Bi doped Cerium Oxide buffer layer was optimized at lowering sintering temperature to prevent a La2Zr2O7 impurity reaction, the improved electrochemical performance was achieved at the maximum power density (MPD) of ~1.43 W cm-2 at 800 oC. The high substitution of La3+ into the ceria lattice improves the oxygen non-stoichiometry of LDC, leading to improve the oxide ion supplying of the cathode side during the high current operation. Consequently, we firstly propose that the larger oxygen storage or supplying capacitance (OSC) effect of the interdiffusion layer composition (La, Zr, Ce, Y)O2 in La-doped CeO2 (LDC) is responsible for the positive enhancement of the oxygen reduction reaction (ORR) at high current ranges through interstitial oxygen supply at the cathode/electrolyte interface rather than (Gd, Zr, Ce, Y)O2 in GDC. The OSC of the LDC is higher than that of the GDC, and it effectively enhances the electrochemical performance of the cathode interface in the SOFCs because it may be affected by the high oxygen carrier concentration of the LDC, the higher oxygen releasing, and storage capacitance. This revealed that the effect of oxygen releasing, and storage capacity of the buffer layer might be the cause of improved performance. Consequently, the cell containing the high OSC buffer layer fabricated at 1250 oC to avoid interfacial insulating layers, such as La2Zr2O7 impurities, successfully displayed a dramatically high-power density value. Figure 1

X-ray nano-spectroscopy study of two solid oxide cells operated for long-term in steam electrolysis

This study addresses the degradation mechanisms of porous fuel electrode from an electrode (Ni/YSZ) and an electrolyte (Ni/CGO)-supported cell operated for long-term in steam electrolysis mode. Using a nanobeam, spatially resolved X-ray fluorescence and X-ray absorption spectroscopy are combined to acquire high-resolution compositional maps and to probe intra-granular changes with the evolution of the Ni chemical state. This experimental work highlights oxidized states of nickel (i.e. NiO/Ni(OH)2 species) in the case of Ni/CGO while for Ni/YSZ the chemical state is metallic. In both types of fuel electrodes, the Ni depletion occurs and the depletion length is reduced to around 1 μm in the case of Ni/CGO after 23,000 h in contrast to around 4 μm in the case of Ni/YSZ after 6100 h. In the case of Ni/CGO, the coating of Ni particles by the diffusion of Gd and Ce from the CGO contact layer prevents the Ni migration while in the case of Ni/YSZ the Ni migration is not suppressed. These results are in accordance with in-situ impedance data where the main difference observed between Ni/YSZ and Ni/CGO fuel electrodes is a deactivation of the fuel electrode as non-ohmic losses for Ni/YSZ in contrast to Ni/CGO.

Direct and pulse electroplating effects on the diffusion barrier property of plasma-nitrided Cr coatings on HT9 steel

The introduction of a Cr and chromium nitride multi-coating barrier between the nuclear metallic fuel and the cladding is a potential candidate to mitigate fuel cladding chemical interaction (FCCI). Cr coatings were electroplated on HT9 disks using direct and pulse currents followed by plasma nitriding for synthesizing additional nitride coating. The pulse current induced Cr coatings revealed severe microstructural changes from crack-free to the abundance of cracks during the plasma nitriding due to phase transformation during the plasma nitriding. The phase transformation of hexagonal CrH to cubic Cr occurred at a temperature as low as 110 °C resulting in the liberation of hydrogen pores agglomerated at Cr grain boundaries and internal stress. Finally, the diffusion barrier property of the pulse current induced Cr coatings was significantly reduced, while the plasma-nitrided Cr coating produced by a direct current exhibited a crack-closure effect, and an additional nitride layer successfully hindered the elemental diffusion of Ce and Nd at 650 °C for 25 h. This current study points to the critical effect of current waveforms on the final barrier property of Cr-chromium nitride coatings for nuclear cladding applications.

Domesticating circular economy? An enquiry into Norwegian subnational authorities’ process of implementing circularity

ABSTRACT This article focuses on the introduction of the concept of circular economy into a Norwegian context by concentrating on two levels of subnational authorities against the backdrop of the national level. By drawing on recorded qualitative data collected in the region of Trøndelag and Oslo, we deploy the concept of domestication to analyse how the diffusion of CE as a political, future-oriented concept is appropriated, i.e. through symbolic, practical and cognitive dimensions. Additionally, we consider the performativity of the future as a component in the adoption of the concept. Our findings suggest that the adoption of CE at these levels of governments in Norway is an ongoing process where the co-construction of the dimensions happens concurrently. Relating to the future, the national level takes a translative approach and goes after an increased interest and activity by private actors. At the first subnational level, in the case of the Trøndelag county, the public sector operates as a channel between knowledge of best practices and private actors who can mobilise action. Meanwhile, at the third subnational level, we find at the municipality of Trondheim, a public authority that proactively changes specific practices and regulates (or normalizes) the CE through their own means.

Tailoring electron transfer with Ce integration in ultrathin Co(OH)2 nanosheets by fast microwave for oxygen evolution reaction

The vertically stacked ultra-thin Co(OH) 2 nanosheets endow the good dispersion of Ce doping. The close integration of Ce into Co(OH) 2 assisted by microwave synthesis promotes electron transfer through “ d – f electronic ladders”, contributing to enhanced OER. • Loose Co(OH) 2 facilitates the diffusion of Ce for large active surface and defects. • Ce incorporation is achieved by high pressure microwave with instantaneous heating. • The intimate CeOx/Co(OH) 2 may tailor electron transfer by “d-f electron ladders”. • The optimized Ce0.21@Co(OH) 2 exhibits excellent activity and stability for OER. The intrinsic activity of Co(OH) 2 for oxygen evolution reaction (OER) may be elaborately improved through the suitable valence adjustment. Ce modification at electronic level is proved to be an efficient strategy owing to the flexible transformation of Ce 3+ /Ce 4+ . Herein, Ce 0.21 @Co(OH) 2 with the optimized Ce doping have been fabricated to tailor the fast electron transfer for the enhanced activity and stability for OER. Firstly, the obtained core–shell structure composed of vertical loose Co(OH) 2 sheets not only exposes a large number of active sites, but also provides channels for Ce doping. Secondly, the high pressure microwave with instantaneous heating can fast introduce Ce into Co(OH) 2 , obtaining Ce x @Co(OH) 2 with well dispersion and close integration. The intimated interaction between Ce and Co species may provide the “ d–f electronic ladders” for accelerating electron transfer of the catalytic surface. Meanwhile, Ce promotes the formation of Co-superoxide intermediate and/or the release of oxygen, which is considered to be the rate-determining step for OER. The electrochemical measurements confirmed the low overpotential of 300 mV at 10 mA cm −2 and great stability of Ce 0.21 @Co(OH) 2 for OER. This work demonstrates a meaningful approach to realize the tuned electronic structure through metal doping.

Studying the effects of thermally diffusing Ce into the surface of YAlO3 for associated particle imaging

Active radiation environments and high-rate backgrounds pose a significant challenge towards improving the detection and characterization of Special Nuclear Material (SNM) using Associated Particle Imaging (API). Ongoing research seeks to reduce the sensitivity of a charged particle, or associated particle, detector to x-ray backgrounds through the creation and characterization of an alpha-sensitive, Ce-doped surface region of Yttrium Aluminium Perovskite (YAP). A wet-chemical layer of trivalent cerium (III) acetylacetonate hydrate was thermally diffused with a reducing atmosphere into single YAP crystals for a temperature range of 800 °C to 1500 °C. The diffusion concentration profile of the cerium compound was assayed with Rutherford Backscattering Spectrometry (RBS), where the Ce diffusion activation energy and the pre-exponential factor within YAP were found to be 1.02±0.10 eV and 9.7±2.0×10-15m2s-1, respectively. Resulting transient polycrystalline structural features at the surface of the YAP crystals were investigated with X-Ray Diffraction (XRD). YAP, Yttrium Aluminium Garnet (YAG), and Yttrium Aluminium Monoclinic (YAM) phases were identified, as well as contributions from Y2O3, CeO2, Ce2O3, and the metastable hexagonal polymorph of YAlO3 (YAH). The luminescent responses of the complex surface layers to x-ray and α excitement were examined as functions of annealing temperature. Radioluminescence emissions typical of the Ce3+4f → 5d transition occupying both the Y3+ and Al3+ sites in YAP and YAG were observed. The brightness of the samples under alpha radiation increased as a function of diffused Ce concentration until the point of optical darkening.

Influence of the Plasma of Pd–Ce/Porous Biomass Carbons Catalysts on the Surface Texture with Enhance Catalytic Activity Toward CO Oxidation

The porous biomass carbons (PBCs) as catalyst supports were synthesized by simple hydrothermal and carbonization method, and the surface property of PBCs were designed by plasma treatment technology. The Pd and Ce loaded TPBCs (PBCs were treated with plasma) supports were evaluated for their catalytic activity in the CO oxidation reaction. The Pd–Ce/TPBCs-20 catalyst (Conditions: CO concentration: 1 vol%, Total flow rate: 50 mL min−1, Moisture: 4 vol%) exhibited the highest catalytic activity, and the complete conversion temperature (T100) was about 20 °C for CO catalytic oxidation. Moreover, the Pd–Ce/TPBCs-20 catalyst behaved an excellent stability with the CO conversion rate in the presence of moisture, remaining higher than 90% after 24 h on stream at 20 °C. Raman, XPS, H2-TPR and O2-TPD analysis revealed that the surface oxygen-containing functional groups and defect concentration will increase with increasing plasma treatment time, which could improved Pd and Ce diffusion and Pd–O–Ce bonding interactions, resulting in increased CO catalytic activity. In addition, chitosan as the raw material for the synthesis of PBCs support, is low-cost and easy to be obtained from nature. Therefore, the Pd–Ce/TPBCs catalysts have great potential for catalytic removal of CO in practical application.

Table-like magnetocaloric effect and enhanced refrigerant capacity of HPS La(Fe,Si)13-based composites by Ce–Co grain boundary diffusion

The structure and magnetic properties of LaFe11.6Si1.4/Ce40Co60 bulk composites prepared by hot pressing sintering (HPS), followed by high-temperature diffusion annealing, were investigated. During the HPS process, the La(Fe,Si)13 alloy powder particles combined with Ce40Co60 binder and a porous structure with high mechanical strength were obtained. The addition of Ce40Co60 can also promote the peritectic reaction. Annealing has important effects on the magnetocaloric properties due to the diffusion of Ce and Co into the La(Fe,Si)13 phase during annealing. HPS samples were annealed at 1373 K for 24 h, and a table-like magnetocaloric effect, exhibiting a constant high magnetic entropy change (− ∆SM) of ~ 4.0 J/(kg K) in a commercially useful temperature region of 28 K (236–264 K), was obtained for a field change of 2 T. The values of full width at half maximum of (− ∆SM)–T plots (ΔTFWHM) and enhanced refrigeration capacity for the composites are 55 K and 173 J/kg, respectively, for a field change of 2 T. The composites exhibit high compressive strength of up to 312 MPa. The present results indicate that LaFe11.6Si1.4/Ce40Co60 bulk composites can meet the requirement of near room temperature magnetic refrigeration based on the Ericsson cycle.

High-temperature interaction of Ce–Fe–As ternary system

The high-temperature interaction within a Ce–Fe–As ternary system in a special barrel-shaped cylinder machined by industrial iron was investigated by x-ray diffraction, backscattered electron imaging, and optical microscopy after heated preservation at 1273 K for 50 h. Results showed that the main phases of Ce–Fe–As interaction at high temperature were CeAs, Fe2As, and a small amount of As dissolved in Fe. Increased atomic ratio of Ce to As had minimal effect on the phase change of the sample. Due to iron diffusion, the phase of Fe2As was found near the cylinder-body matrix but not in the center area of the sample. A transition area where Fe, Ce, and As coexisted was observed between the areas whereas Ce–As and Fe–As coexisted. The diffusion of As into the Ce–Fe–As system occurred through the formation of Fe2As, and Ce diffusion occurred through the vacancy mechanism.

Micromagnetic simulation for the effects of core-shell distributions of RE on the magnetic properties of dual-main-phase Nd-Fe-B based magnets

Abstract Inspired by the experimental discovery, the effects of core-shell distributions of RE on the properties of the dual-main-phase rare earth-iron-boron (RE-Fe-B) magnets are investigated by micromagnetic simulation. In the dual-main-phase (DMP) magnets containing two main phases of hard magnetic Ce-free and Ce-rich RE2Fe14B, the nucleation tends to occur in the Ce-rich RE2Fe14B grains due to their low anisotropy field. The coercivity of dual-main-phase magnets without core-shell distributions of RE is much lower than that of the single-main-phase (SMP) magnets with the same nominal composition, though the Ce-rich RE2Fe14B grains are dipolar coupled by the Ce-free RE2Fe14B grains. The formation of core-shell distributions of RE main phase in DMP magnets adjusts their magnetic behavior. The appearance of the Nd-rich shells in the Ce-rich RE2Fe14B phases due to Nd diffusion will retard the nucleation of reversal domain because of the increased anisotropy field of the grain surface. The demagnetizing field of the Nd2Fe14B phases is also decreased by the shell structure, which further reduces the possibility of the nucleation. On the other hand, the formation of the shells by Ce diffusion in the Nd2Fe14B phase will promote the nucleation of reversal domain due to the reduced surface anisotropy field. It can increase the demagnetizing field of the Ce-rich RE2Fe14B phases and therefore increase the possibility of the nucleation. Hence, good magnetic properties can be only obtained in the DMP magnets with more Nd diffusion and less Ce diffusion, which is consistent with the experimental results.

Thermal diffusion of mixed valence Ce in 6Li loaded silicate glass for neutron imaging

The creation and characterization of Ce doped surface regions in 6Li enriched silicate glasses for cold neutron detection is described. A diffusion layer of a dried solution containing cerium III acetylacetonate hydrate was thermally diffused into monolithic glass samples under a reducing atmosphere. The diffusion characteristics of the mixed valence cerium compound were assayed with Rutherford Backscattering Spectrometry. The Ce diffusion activation energy within the glass was found to be 411 ± 53 kJ/mol (4.26 ± 0.55 eV). Radiation induced color centers formed on the diffusion samples as an effect of using alpha bombardment measurements. The ratio of Ce valence states of the diffused cerium was assayed as a function of depth with X-ray Photoelectron Spectroscopy, and the signal from Ce for the color centers was compared to the unirradiated sample surface.

Microwave effect on barium strontium ferrate and co-fired fuel cells

The microwave effect on barium strontium ferrate (BSF) was determined, and core-shell BSF-xCe cathode was co-fired with ceria-based electrolyte in a focused microwave cavity. The solubility of cerium (Ce) in BSF was up to x = 10 mol%. The grain size of the microwave-sintered BSF was smaller. The conductivity of BSF-20Ce cathode with the lower transition temperature was significantly higher than that obtained by conventional sintering. The ohmic (Rohm) and electrode polarization (Rp) resistances of the fuel cells were significantly reduced. The open-circuit voltage and peak power density of the microwave co-fired fuel cells increased with the Ce coatings. The high ionic conductivity at high operation temperature was due to the generation of more oxygen vacancies without clustering, caused by the effective absorption of microwave by the low valence iron oxide. Thus, the enhanced diffusion of Ce and the reduced Rp and Rohm by the microwave energy improved the performance of fuel cells.

The Effects of Cerium Migration on PEM Fuel Cell Performance

Cerium enhances the durability of polymer electrolyte membrane (PEM) fuel cells by scavenging reactive radical species which are generated during operation. However, during cell fabrication, conditioning, and discharge, Ce migrates through-plane between the PEM and catalyst layers (CLs) due to concentration and potential gradients.1,2 In addition, we have observed in-plane Ce migration due to water gradients and also identified degradation of Ce-exchanged PEM side chains as another possible mechanism for Ce migration.3 Ce migration is detrimental because (1) its accumulation in the CL ionomer can diminish the electrode’s proton conductivity, which generates performance losses4; and (2) its depletion may leave an ionomer region more susceptible to radical attack. Therefore, it is critical to understand the relative influence of different migration mechanisms under a range of operating conditions in order to stabilize Ce in the PEM and localize it to areas of highest radical generation. To understand the effects of potential gradients and relative humidity (RH) on Ce migration, ex situ experiments were performed using uncatalyzed Nafion® XL PEMs (DuPont) which contain ~6 μg/cm2 ion-exchanged Ce. PEM specimens were operated in H2 pump mode in a standard conductivity cell (BekkTech) at 80°C with 50% and 100% RH H2. The evolution of Ce profiles was quantified using X-ray fluorescence (XRF). By comparing the resulting profiles at 4 C of charge transfer for the different potential and RH conditions (Figure 1a), we observe decreased Ce transference at low RH. Under these conditions, decreased PEM water content causes a disproportionate reduction in Ce conductivity relative to proton conductivity. In these experiments, Ce ion mobility induced by a potential gradient leads to a concentration gradient, which, in turn, induces Ce diffusion in the opposite direction. Therefore, the profiles shown in Figure 1a arise from a combination of ion mobility and back-diffusion due to the resulting concentration gradient. In order to decouple these effects, a transient, 1-D model was developed based on Nernst-Einstein ion mobility and Fickian diffusion, in order to solve for the ion mobility and diffusion coefficients. Experimental and model results for the 2 V, 100% RH case are shown in Figure 1b. At 100% RH, both diffusion and ion mobility coefficients were determined to be an order of magnitude higher than at 50% RH. In addition to migration within the PEM, Ce is stabilized in the cathode CL, likely in the CL ionomer and/or carbon CL supports.3 Ce accumulation in the cathode catalyst layer was measured to degrade MEA performance. Different mechanisms have been proposed for the performance loss, including increased proton resistance within the CL, and a reduction of oxygen reduction reaction kinetics. However, the effect of each mechanism on performance loss is difficult to quantify. The relative influence of Ce poisoning on the cathode CL performance will also be discussed. Quantifying the different Ce migration mechanisms has provided a better understanding of the effects of Ce migration in the PEM and CL and the associated losses in operating performance. These results demonstrate that stable Ce compounds, which can be localized to areas of highest reactive radical generation, need to be developed to enhance PEFC durability without compromising performance. Acknowledgements This research is supported by the U.S. DOE Fuel Cell Technologies Office, through the Fuel Cell Performance and Durability (FC-PAD) Consortium; Fuel Cells Program manager: Dimitrios Papageorgopoulos. Prof. Ajay Prasad and Prof. Suresh Advani also acknowledge support from the University of Delaware’s Fuel Cell Bus Program. This program is funded by the Federal Transit Administration at the Center for Fuel Cell Research at the University of Delaware. References Stewart, S. M.; Spernjak, D.; Borup, R.; Datye, A.; Garzon, F. ECS Electrochem. Lett. 3, F19–F22 (2014).Baker, A. M.; Mukundan, R.; Spernjak, D.; Advani, S. G.; Prasad, A. K.; Borup, R. L. ECS Trans. 75, 707–714 (2016)Baker, A. M.; Mukundan, R.; Spernjak, D.; Judge, E. J.; Advani, S. G.; Prasad, A. K.; Borup, R. L. J. Electrochem. Soc. 163, F1023–F1031 (2016).Banham, D.; Ye, S. Y.; Cheng, T.; Knights, S.; Stewart, S. M.; Wilson, M.; Garzon, F. J. Electrochem. Soc. 161, F1075–F1080 (2014). Figure 1

Multi-scale analysis of the diffusion barrier layer of gadolinia-doped ceria in a solid oxide fuel cell operated in a stack for 3000 h

The state-of-the-art materials for SOFCs are yttria-stabilized zirconia as electrolyte and lanthanum strontium cobalt ferrite as cathode. However, the formation of insulating phases between them requires the use of diffusion barriers, typically made of gadolinia doped ceria. The study of the stability of this layer during the fabrication and in operando is currently one of the major goals of the SOFC industry. In this work, the cation inter-diffusion at the cathode/barrier layer/electrolyte region is analysed for an anode-supported cell industrially fabricated by conventional techniques, assembled in a short-stack and tested under real operation conditions for 3000 h. A comprehensive study of this cell, and an equivalent non-operated one, is performed in order to understand the inter-diffusion mechanisms with possible effects on the final performance. The analyses evidence that the cation diffusion is occurring during the fabrication process. Despite the significant diffusion of Ce,Gd, Zr, Y and Sr cations, the formation of typically reported CGO-YSZ solid solution is not observed while the presence of isolated grains of SrZrO3 is proved. All in all, this study presents new insights into the stability of the typically employed diffusion barriers for solid oxide cells that will guide future strategies to improve their performance and durability.

Microstructure Evolution of Novel Al-Cu-Li-Ce Alloys during Homogenization

The present work is aimed to clarify the formation of the τ 1 (Al 8 Cu 4 Ce) phase and its formation mechanism in the high Cu content alloys with Ce addition, i.e high Cu/Li Al-Cu-Li-Ce alloys. The microstructure evolution of the alloy during the two-step homogenization annealing process was investigated. Results show that the coarse Ag+Mg enriched T B (Al 7 Cu 4 Li) phase and the primary AlCuCe phase occur under solidification. Two types of the minor τ 1 phases are formed after homogenization. It is concluded that the τ 1 phase nucleation mechanism could involve either nucleation on an existing T B phase by Ce diffusion from the Al matrix or the transformation of the primary AlCuCe phase into the τ 1 phase by Ce diffusion through the coarse primary AlCuCe phase shrink. It is deduced that the grain refinement is attributed to the primary AlCuCe, which can promote α (Al) nucleation and further prohibit the grain growth for the experimental alloy.

Ostwald Ripening Behavior of Al8CeCu4 Phase in Al-14Cu-7Ce Alloy

The Ostwald ripening behavior of Al 8 CeCu 4 phase in the Al-14Cu-7Ce alloy annealed at elevated temperatures was investigated using hardness testing, scanning electron microscopy, image analyses and physical modeling. Results indicate that the average radius of Al 8 CeCu 4 particles increases while the hardness of the alloy decreases with increasing of annealing temperature and time. The ripening process of Al 8 CeCu 4 phase is mainly controlled by the volume diffusion of Ce. The ripening kinetic of Al 8 CeCu 4 particles satisfies well the modified Lifshits-Slyozov-Wagner theory, taking into account the effect of the volume fraction of Al 8 CeCu 4 particles. The volume diffusion coefficient of Ce and the interfacial energy between the matrix and Al 8 CeCu 4 phase were also calculated based on the general rate equation.

Asymmetric diffusion of Zr, Sc and Ce, Gd at the interface between zirconia electrolyte and ceria interlayer for solid oxide fuel cells

The microstructures of cathode interlayer and elemental diffusion behaviors across the interfacial region (electrolyte/interlayer) have been characterized using high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and scanning TEM combined with energy dispersive X-ray spectroscopy (STEM-EDS). A densified film about 100 nm is locally formed at the interface of electrolyte/interlayer as the interlayer using dip-coating method and being sintered at 1200 °C. It is observed that the compositional distribution curves across the interface are asymmetric. More amount of the Zr, Sc component is detected in gadolinium-doped ceria (GDC) than that of the Ce, Gd component is detected in scandia-stabilized-zirconia (SSZ). XRD and EDS results show that the densified layer might consist of (Zr, Ce)O2-based solid solution. The high open circuit voltage of the cell is related to the dense structure of electrolyte, while the increased activation energy in overpotential resistance is attributed to the porous structure of interlayer as well as the high resistance phases locally formed at its interface.

Diffusion Processes Between the Barrier Cathodic Layer and the Electrolyte of a Solid-Oxide Fuel Cell

We study the influence of reducing and oxidizing media on the mutual diffusion of chemical elements between the (Ce,Gd)O2–δ barrier (protective) cathodic layer and the YSZ electrolyte of a solid-oxide fuel cell in the course of annealing at 1400°С. The results of the analysis of distributions of chemical elements in annealed specimens demonstrate that, in the case of annealing in the reducing medium, the diffusion of Ce and Gd into the electrolyte is more intense than the diffusion of Zr from the electrolyte into the protective layer. As compared with the oxidizing medium (air), the mutual diffusion of Ce, Gd, and Zr in the reducing (hydrogen-containing) medium is much more intense and the depth of their penetration is 1.5–3 times larger.

Atomic scale investigation of Si and Ce‐rich nanoclusters in Ce‐doped SiO1.5 thin films

AbstractThe optical properties and the nanoscale structure of Ce‐doped SiO1.5 thin films elaborated by evaporation were investigated by photoluminescence and atom probe tomography. Strong Ce‐related blue luminescence is observed on the 1100 °C annealed sample. Atom probe tomography experiments give evidence of the formation of a cerium silicate having a stoichiometry compatible with Ce2Si2O7. Moreover, we further observe the formation of pure Si nanocrystals (Si‐ncs) which results from the phase separation of the SiO1.5 film. No optical signal from Si‐ncs was observed at least for the 3% Ce‐doped SiO1.5 film considered in this study. We analyze the size distribution of both Si‐ncs and Ce2Si2O7 particles. Finally, the Si and Ce diffusion coefficients were estimated based on atom probe tomography characterizations. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)