Electrical conductivity and defect equilibria of Pr0.1Ce0.9O(2-δ)

Praseodymium-cerium oxide (PCO) solid solutions exhibit mixed ionic electronic conductivity (MIEC) behavior in a relatively high and readily accessible oxygen partial pressure (P(O(2))) regime and as such serve as a model system for investigating the correlation between thermodynamic and kinetic properties and performance figures of merit in the areas of high temperature energy conversion, automotive control, and gas sensing applications. In this paper, we present measurements on the non-stoichiometry of Pr(0.1)Ce(0.9)O(2-δ) and develop a defect equilibria model to predict the dependence of the concentration of all the dominant charge carriers on temperature, P(O(2)), and Pr fraction. The predictive model is then employed to describe the measured electrical conductivity and oxygen nonstoichiometry whereby pre-exponentials and enthalpies of defect formation and migration are extracted.     

Electronic conductivity of Ce0.9Gd0.1O(1.95-δ) and Ce0.8Pr0.2O(2-δ): Hebb-Wagner polarisation in the case of redox active dopants and interference

The electronic conductivity of Ce(0.9)Gd(0.1)O(1.95-δ) and Ce(0.8)Pr(0.2)O(2-δ) under suppressed ionic flow was measured as a function of pO(2) in the range from 10(3) atm to 10(-17) atm for temperatures between 600 °C and 900 °C by means of Hebb-Wagner polarisation. The steady state I-V curve of Ce(0.9)Gd(0.1)O(1.95-δ) could be well described by the standard Hebb-Wagner equation [M. H. Hebb, J. Chem. Phys., 1952, 20, 185; C. Wagner, Z. Elektrochem., 1956, 60, 4], yielding expressions for the n- and p-type conductivity as a function of pO(2). On the other hand, significant deviation of the steady state I-V curve from the standard Hebb-Wagner equation was observed for the case of Ce(0.8)Pr(0.2)O(2-δ). It is shown that the I-V curve can be successfully reproduced when the presence of the redox active dopant, Pr(3+)/Pr(4+), is taken into account, whereas even better agreement can be reached when further taking into account the interference between the ionic and electronic flows [C. Chatzichristodoulou, W.-S. Park, H.-S. Kim, P. V. Hendriksen and H.-I. Yoo, Phys. Chem. Chem. Phys., 2010, 12, 33]. Expressions are deduced for the small polaron mobilities in the Ce 4f and Pr 4f bands of Ce(0.8)Pr(0.2)O(2-δ).     

Evaluation of kinetic stability against CO2 and conducting property of BaCe0.9−xZrxY0.1O3−δ

In order to prepare high proton conducting oxide with high chemical stability against CO₂ at 600–800 °C, preparation of BaCe_0.9?xZr_xY_0.1O_3?δ was examined. Almost single-phase could be prepared for the specimens with x = 0.0–0.2 by Pechini method. Reaction kinetics between BaCe_0.9?xZr_xY_0.1O_3?δ and CO₂ could be explained by Jander model. With increasing Zr content up to 0.2, apparent rate constant determined from Jander plot decreased by about one order, showing improvement of kinetic stability against CO₂. It was also clarified that influence of partial Zr substitution on electrical property was slight, leading to the conclusion that BaCe_0.7Zr_0.2Y_0.1O_3?δ exhibited both high kinetic stability against CO₂ and relatively high proton conduction.     

Sol–gel synthesis and catalytic property of Ce1−x Ti x O2 nanocomposites supported on attapulgite clay

Ce_1?x Ti _x O₂ nanocomposites supported on attapulgite clay (Ce_1?x Ti _x O₂/ATP) were prepared by a facile sol–gel route. The textural and structural properties of the prepared products were characterized by thermogravimetric-differential scanning calormetry analysis, X-ray diffraction, transmission electron microscopy, energy-dispersive spectrometry, Fourier transform infrared spectroscopy and Nitrogen adsorption-desorption measurements. The catalytic activity of the prepared Ce_1?x Ti _x O₂/ATP catalysts for rhodamine B degradation was investigated. Results indicate that the particle size of Ce_1?x Ti _x O₂ nanoparticles evenly attached onto the surface of ATP is approximately 10 nm. The Ti⁴⁺ doping ratios exhibit considerable impact on the redox ability and catalytic activity of Ce_1?x Ti _x O₂/ATP composites. The introduction of an optimal amount of Ti⁴⁺ contributes to forming structure defects and electronic defects in the oxide lattice, increasing concentration of oxygen vacancies, consequently improving low-temperature redox ability of Ce⁴⁺ and enhancing catalytic activity of the composites. Ce_1?x Ti _x O₂/ATP (x = 0.5) catalyst has the best catalytic degradation efficiency, which can reach as high as 97 % after reaction for 240 min. It is also found that attapulgite clay exhibit a positive synergistic effect to the Ce_1?x Ti _x O₂ nanoparticles.     

Mechanism of oxygen transfer in layered lanthanide nickelates Ln2 − x NiO4 + δ (Ln = La, Pr) and their nanocomposites with Ce0.9Gd0.1O2 − δ and Y2(Ti0.8Zr0.2)1.6Mn0.4O7 − δ solid electrolytes

The mechanism of oxygen transfer in layered nickelates having a Ruddlesden-Popper structure and their nanocomposites with Ce_0.9Gd_0.1O_{2 ? δ} (GDC) and Y₂(Ti_0.8Zr_0.2)_1.6Mn_0.4O_{7 ? δ} (YTZM) solid electrolytes having fluorite and pyrochlore structures were studied by the oxygen isotope heteroexchange method in a flow and static reactor, thermoprogrammed desorption, and semiempirical interacting bonds method. The experimental heteroexchange data were adequately described by assuming that all atoms were equivalent in exchange in the bulk of layered nickelates, which was consistent with the cooperative oxygen migration model with fast exchange between the interstitial and regular positions. Strong interaction between the domains of the nickelate phases and solid electrolytes in nanocomposites, accompanied by a redistribution of cations between the phases, hindered the cooperative oxygen migration and led to a decrease in the diffusion coefficient as the exchange rate increased.     

Electrochemical performance and stability of nano-particulate and bi-continuous La1−X Sr X CoO3 and Ce0.9Gd0.1O1.95 composite electrodes

A bi-continuous porous cathode consisting of nano-particles of strontium substituted lanthanum cobaltite (LSC) covering the surface of a Ce_0.9Gd_0.1O_1.95 (CGO10) backbone has been produced. The polarization resistance (R _P) of this cathode was measured to ～35 mΩ cm² at 650 °C. The area-specific resistance at 650 °C (ASR) when applied onto an anode supported cell (ASC) was found to increase from 540 to 730 mΩ cm² when subjected to a thermal cycle to 850 °C. This effect was attributed to particles coarsening but also to a reaction with the electrolyte. The results imply that a CGO10 barrier is required for this type of nano-structured cathode.     

Optimization of the electrochemical performance of a Ni/Ce0.9Gd0.1O2−δ-impregnated La0.57Sr0.15TiO3 anode in hydrogen

A-site deficient perovskite La_0.57Sr_0.15TiO₃ (LSTO) materials are synthesized by a modified polyacrylamide gel route. X-ray diffraction pattern of LSTO indicates an orthorhombic structure. The thermal expansion coefficient of LSTO is 10.0 × 10⁻⁶ K⁻¹ at 600 °C in 5%H₂/Ar. LSTO shows an electrical conductivity of 2 S cm⁻¹ at 600 °C in 3%H₂O/H₂. A new composite material, containing the porous LSTO backbone impregnated with small amounts of Ce_0.9Gd_0.1O_2−δ (CGO) (3.4–8.3 wt.%) and Ni/Cu (2.0–6.3 wt.%), is investigated as an alternative anode for solid oxide fuel cells (SOFCs). Because of the substantial electro-catalytic activity of the fine and well-dispersed Ni particles on the surface of the ceramic framework, the polarization resistance of 6.3%Ni-8.3%CGO-LSTO anode reaches 0.73 Ω cm² at 800 °C in 3%H₂O/H₂. In order to further improve the anodic performance, corn starch and carbon black are used as pore-formers to optimize the microstructure of anodes.     

Synthesis and photoluminescent properties of Y1 − x La x PO4:Eu3+ nanophosphor

In this paper, Y_{1 ? x} La _x PO₄:Eu³⁺ (x = 0.5, 0.7, and 0.3) nanophosphors were synthesized by a rather simple method. The products present different morphologies. For Y_{1 ? x} La _x PO₄:Eu³⁺, they have similar phase composition of a mixture of monoclinic LaPO₄ and tetragonal YPO₄. Furthermore, the luminescence behavior of Eu³⁺ has been investigated in this type of matrices. In Y_{1 ? x} La _x PO₄:Eu³⁺, the ⁵D₀-⁷F₁ magnetic dipole transition is dominant, indicating that the Eu³⁺ site is inversion symmetry. The difference in the Eu-O charge transfer (CT) band with La³⁺ ion concentration suggests the difference in the ionicity of the Eu-O bond. Among those products, the red to orange intensity ratio (R/O) of ⁵D₀-⁷F₂ to ⁵D₀-⁷F₁ value of Eu³⁺ is different, furthermore, for La³⁺ x = 0.3, the R/O value of Eu³⁺ is the biggest on the contrary, indicating that the inversion symmetry Eu³⁺ is lowest.     

Functional properties and electrochemical performance of dual-phase Pr0.9Y0.1BaCo2O6−δ–Ce0.8Sm0.2O1.9 composite cathodes

Journal of Solid State Electrochemistry - The dual-phase composites are obtained by mixing perovskite-like cobaltite Pr0.9Y0.1BaCo2O6–δ and samarium-doped ceria Ce0.8Sm0.2O1.9 in weight...     

Nd0.6-xBaxSr0.4Co0.2Fe0.8O3-δ-30％Ce0.9Gd0.1O1.95复合阴极的性能

采用溶胶-凝胶法合成了Nd0.6-xBaxSr0.4Co0.2Fe0.8O3-δ(NBSCF)阴极粉体和Ce0.9Gd0.1O1.95(GDC)电解质粉体.利用X射线衍射仪(XRD)、电子能谱仪(XPS)分别对NBSCF的结构及其与GDC的化学相容性、NBSCF表面的化学状态进行表征.用直流四端子法和交流阻抗谱法分别测...     

Synthesis and study of the properties of the solid solutions K2Y1−x Tb(Tm) x (MoO4)(PO4) and K2Y1−x Tm x (MoO4)(PO4)0.95(VO4)0.05

The solid solutions K₂Y_1?x Tb(Tm) _x (MoO₄)(PO₄) and K₂Y_1?x Tm _x (MoO₄)(PO₄)_0.95(VO₄)_0.05 were synthesized, which are isostructural and crystallize in the orthorhombic crystal system (space group Ibca). The luminescence intensity of the terbium-containing samples increases with increase in the terbium content. The thulium-containing samples are characterized by intense luminescence in the blue spectral region and concentration quenching of luminescence. The introduction of the vanadate anion adversely affects the luminescence intensity.     

Structure,chemical stability and electrical properties of BaCe0.9Y0.1O3−δ modified with V2O5

Wet vacuum impregnation method was applied in order to evaluate the possibility of the formation of the material in BaCe_0.9Y_0.1O_3?δ–V₂O₅ system. Single-phase BaCe_0.9Y_0.1O_3?δ samples, synthesised by solid-state reaction method, were impregnated with the solution of vanadium(V) oxide precursor. Multi-step, multi-cycle impregnation procedure was applied to enhance the impregnation efficiency. Partial decomposition of Y-doped BaCeO₃ in contact with the solution of the precursor, resulting in the formation of vanadium containing phases (CeVO₄ and BaV₂O₆) on the materials surface, was observed. However, the presence of vanadium was also confirmed for the inner parts of the materials. The synthesised materials were submitted for exposition test to evaluate their chemical stability towards CO₂/H₂O. All BaCe_0.9Y_0.1O₃-based materials modified by impregnation revealed higher chemical stability in comparison with single-phase un-modified BaCe_0.9Y_0.1O_3?δ, since the amount of barium carbonate formed during the exposition was significantly lower. The total electrical conductivity of the received multi-phase materials was generally slightly lower than for the reference BaCe_0.9Y_0.1O_3?δ sample, since the presence of the additional phases had a blocking effect on materials conductivity. The values of BaCeO₃ lattice parameters and the Seebeck coefficient did not show the modification of the defects structure of Y-doped BaCeO₃ during applied synthesis procedure.

     

Electrochemical performance of LaNi0.6Co0.4O3-δ–Ce0.9Gd0.1O1.95 composite electrode and evaluation of its effective reaction length

Journal of Solid State Electrochemistry - The electrochemical properties of LaNi0.6Co0.4O3-δ–Ce0.9Gd0.1O1.95 composite electrodes as a function of temperature and p(O2) were investigated...     

Characterization of superparamagnetic Mg x Zn1−x Fe2O4 powders

Structural and magnetic properties of Mg _x Zn_1−x Fe₂O₄ powders have been studied with respect to the application for thermal cancer therapy (magnetic hyperthermia). Mg _x Zn_1−x Fe₂O₄ (x=0.1–0.5) powders with particle sizes between 5 and 8 nm were produced by citrate method. The X-ray diffraction patterns of the samples correspond to a spinel phase. The lattice constant and the volume of the elementary cell increase when x changes from 0.1 to 0.5. The FTIR-spectra ascertain the spinel phase formation. The Mossbauer studies reveal the presence of extremely small particles, which undergo superparamagnetic relaxation at room temperature. The core-shell model has been applied to explain quadruple doublets. The quadruple splitting at “shells” is bigger than those at “cores” whereas the isomer shifts remain close. Magnetic studies confirm the presence of extremely small particles that behave as superparamagnetic ones.      

Crystal structure and properties of the Na1−x Ru2O4 phase

Sodium ruthenium(III,IV) oxide Na_1−x Ru₂O₄ was synthesized by the solid state reaction of Na₂CO₃ and RuO₂ in inert atmosphere and characterized by X-ray powder diffraction, electron diffraction, and high-resolution transmission electron microscopy. The compound crystallizes in the CaFe₂O₄-type structure (space group Pnma, Z = 4, a = 9.2641(7) Å, b = 2.8249(3) Å, c = 11.1496(7) Å). Double rutile-like chains of the RuO₆ octahedra form a three-dimensional framework, whose tunnels contain sodium cations. The structure contains two crystallographically independent sites of ruthenium atoms randomly occupied by the Ru^III and Ru^IV cations. The superstructure with the doubled b parameter found for one of the samples under study using electron diffraction is caused, probably, by ordering of the Ru cations in the rutile-like chains. The Na_{1− x} Ru₂O₄ compound exhibits temperature-independent paramagnetism with χ₀ = 1.9·10⁻⁴ cm³ (mole of Ru⁻¹). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1655–1660, October, 2006.     

Synthesis and characterization of nano-structured Th1?x Ce x O2 mixed oxide

GEL combustion technique was applied to obtain oxides of thorium and cerium from their respective nitrate solutions using citric acid as the gelating agent. The dried samples were characterized by IR and TG studies. Intermediate and final products during TG studies have been isolated and characterized by XRD studies. All the TG runs during heating of thorium and cerium nitrate with citric acid dried Gels showed a two step process. The weight loss at each step and the X-ray data of the product at each step, helped in suggesting a possible mechanism. Kinetic study was carried out independently for each step. The reaction mechanism as observed during interactive procedure was found to be diffusion controlled. The kinetic parameters (activation energy and pre-exponential factor) for each step in all reactions have been calculated. Observations from XRD studies show that with increase in cerium concentration in the oxides, the lattice parameter values have shown a decreasing trend for all the five compositions studied. It was observed that in TG studies with increase in cerium concentration, the final temperature of the reactions have shown a decreasing trend. SEM studies of the powders reveal that synthesized oxides have a tendency to form agglomerate of varying size ranging from 50 to 100 μm in case of mixed oxides but the size of thorium oxide powder so synthesized have pore size 10–100 μm. SEM images shows that GEL combustion may result in agglomeration, if the temperature is not properly controlled to the desired value. SEM studies also reveal that each agglomerate contains approximately 10–100 individual particles. Surface area of the mixed oxide powders were determined using Gas adsorption technique. The surface area was found to be in the range of 3–17 m²/g in all cases. Specific surface area of thorium oxide was found to be lesser than cerium oxide but in case of mixed oxides surface area decreases with increase in cerium content. Majority of pores, indicating the particle size are in the range of 0.01–0.04 cm³/g.     

Investigation of Pr2NiMnO6‐Ce0.9Gd0.1O1.95 composite cathode for intermediate-temperature solid oxide fuel cells

Journal of Solid State Electrochemistry - The electrochemical performance of Pr2NiMnO6 (PNMO)-xCe0.9Gd0.1O1.95 (CGO) (x = 0–40 wt%) composite oxides as...