Electrochemical properties of solid solutions in the Li8Zr1 − x Ce x O6 system

Li₈Zr_{1 ? x} Ce _x O₆ solid solutions based on lithium zirconate Li₈ZrO₆ were obtained by solid-state synthesis in an inert atmosphere. Their transport properties (the electron component of the total conductivity, the temperature and concentration dependences of conductivity, and the activation energies) were studied by impedance spectroscopy. The practical stability of the ceramic samples of Li₈Zr_{1 ? x} Ce _x O₆ solid solutions (x = 0–0.07) at 473–573 K against melted lithium was studied.     

The Preparation and Characterization of Highly Dispersed PdO over Alumina for Low‐temperature Combustion of Methane

PdO/Al₂O₃ catalysts prepared by glow discharge plasma treatment followed by thermal calcination show a much higher dispersion and a better catalytic activity for methane combustion at relatively low temperatures. The dispersion of palladium active species by such plasma prepared catalysts is 29.7%, 5.4 times higher than that of conventional catalysts. XPS analysis indicates that a surface enrichment of Pd active species (PdO) has been achieved after plasma treatment. The surface atomic composition of PdO of plasma prepared catalysts reaches 10.5%. XRD characterization also confirms a wellcrystallized PdO phase present on the plasma prepared catalyst. The lightoff temperature of the plasma prepared catalyst is 370°C, 50°C lower than that obtained from the conventional catalyst.     

Effect of Zr/Ce molar ratio on the structure of powders and Zr1−x Ce x O2 coatings on quartz fiber reinforced polyimide matrix composites via sol–gel process

In this investigation, Zr_1−x Ce _x O₂ coatings were fabricated on quartz fiber reinforced polyimide matrix composites via sol–gel process at 400 °C. The phase evolution, structural and morphological characteristic of specimens were investigated by differential scanning calorimetric, Fourier transform infrared spectroscopy, powder X-ray diffraction and scanning electron microscopy. The significant phase evolution of final powders with the decreasing Zr/Ce molar ratio could be observed as follows: tetragonal (t′) → cubic + tetragonal (t′) → tetragonal (t″). BET specific surface areas of powders exhibited a decreased tendency with the increasing calcination temperature as well as the decreasing Zr/Ce molar ratio. The average crystallite size and the mean particle size increased with the elevated calcination temperature, while the particle size also increased with the increase in Ce content. The progressive addition of Ce could promote the sintering process and the densification of coating. Morphologies of coatings changed with the variation of the Zr/Ce molar ratio. The results indicate that Zr_0.75Ce_0.25O₂ coating with the Zr/Ce molar ratio of 3 is a stable uniform coating with excellent adhesion.     

Preparation of aqueous sols of Ce1 − x Gd x O2-δ, Y0.9Eu0.1VO4 and nanocomposites Ce1 − x Gd x O2-δ/Y0.9Eu0.1VO4 stabilized by polyacrylic acid

A method for the synthesis of stable aqueous sols of nanocrystalline solid solutions Ce_1?x Gd _x O_2-δ (x = 0.10, 0.15, 0.20) and Y_0.9Eu_0.1VO₄ and nanocomposites Ce_{1 ? x} Gd _x O_2-δ/Y_0.9Eu_0.1VO₄ stabilized by biocompatible low-molecular-weight polyacrylic acid was proposed. Polyacrylic acid was shown to be a promising matrix for the preparation of polyfunctional composite materials.     

Electrophysical properties of solid solutions of Zn2 − x (Zr a Sn b )1 − x Fe2x O4 compositions

The electrophysical properties of the multicomponent Zn₂ZrO₄ ? Zn₂SnO₄ ? ZnFe₂O₄ system are studied. The electrophysical parameters of solid solutions of Zn_{2 ? x} (Zr _a Sn _b )_{1 ? x} Fe_2x O₄ (x = 0–1.0, Δx = 0.1, a + b = 1) are determined. It is found that the formed solid solutions are semiconductors with electrophysical properties that change in a regular fashion with composition and are distinguished by high values of resistivity (107–1012 Ω cm).     

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.     

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.     

Glycolate Ti1 − x Fe x (OCH2CH2O)2 − x/2 as a precursor for the preparation of quasi-one-dimensional (1D) solid solutions Ti1 − x Fe x O2 − 2x/2 (0 ≤ x ≤ 0.1)

Quasi-one-dimensional (1D) solid solutions Ti_{1 ? x} Fe _x (OCH₂CH₂O)_{2 ? x/2} (0 < x ≤ 0.1) with the structure of anatase were prepared by heating the glycolate Ti_{1 ? x} Fe _x (OCH₂CH₂O)_{2 ? x/2} in an atmosphere of air at a temperature of >450°C. The conditions of formation and the properties of the new glycolate Ti₃Fe₂(OCH₂CH₂O)₉ were described. It was found that the synthesized Ti_{1 ? x} Fe _x O_{2 ? 2x/2} solid solutions exhibit photocatalytic activity in the reaction of hydroquinone oxidation in an aqueous solution on irradiation with UV light. A correlation between the rate of oxidation of hydroquinone and the concentration of iron in the catalyst was established. A procedure for the preparation of titanium dioxide with the structure of anatase doped with iron and carbon (Ti_{1 ? x} Fe _x O_{(2 ? x/2) ? yCy)} and also composites on its basis, which contain an excess amount of carbon, was proposed.     

Recent advances in layered LiNi x CoyMn1−x−y O2 cathode materials for lithium ion batteries

Lithium cobalt oxide, LiCoO₂, has been the most widely used cathode material in commercial lithium ion batteries. Nevertheless, cobalt has economic and environmental problems that leave the door open to exploit alternative cathode materials, among which LiNi _x Co_yMn_{1 − x − y} O₂ may have improved performances, such as thermal stability, due to the synergistic effect of the three ions. Recently, intensive effort has been directed towards the development of LiNi _x Co _y Mn_{1 − x − y} O₂ as a possible replacement for LiCoO₂. Recent advances in layered LiNi _x Co_yMn_{1 − x − y} O₂ cathode materials are summarized in this paper. The preparation and the performance are reviewed, and the future promising cathode materials are also prospected.     

Novel red-emitting phosphors, (Mg(1−x−y)MnxDyy)Al2Si2O8 and (Mg(1−x−y)MnxTmy)Al2Si2O8

Mn⁴⁺ doped and Dy³⁺, Tm³⁺ co-doped MgAl₂Si₂O₈-based phosphors were prepared by conventional solid state reaction at 1,300 °C. They were characterized by thermogravimetry, differential thermal analysis, X-ray powder diffraction, photoluminescence, and scanning electron microscopy. The luminescence mechanism of the phosphors, which showed broad red emission bands in the range of 600–715 nm and had a different maximum intensity when activated by UV illumination, was discussed. Such a red emission can be attributed to the ²E → ⁴A₂ transitions of Mn⁴⁺.     

Electrochemical sensors based on platinized Ti1 − x Ru x O2

Electrocatalysts based on platinized titania modified with ruthenia (0–9 mol %) were studied. The synthesized materials were investigated as working electrodes in potentiometric sensors sensitive to hydrogen and carbon monoxide. All electrocatalysts showed reproducible behavior at pure gas concentrations from 400 to 4000 ppm. In CO-H₂ mixtures with comparable concentrations of both gases, the sensors were selective toward hydrogen at ≥0.05 mol % Ru, but not selective to hydrogen or CO at less than 0.05 mol % Ru in the substrate.     

Ionic conductivity and crystal chemistry of ramsdellite type compounds,Li2+x(LixMg1−xSn3)O8, 0 ≤ x ≤ 0.5 and Li2Mg1−xFe2xSn3−xO8, 0 ≤ x ≤ 1

Solid solution phases Li_2+x(Li_xMg_1−xSn₃)O₈: 0 ≤ x ≤ 0.5 and Li₂Mg_1−xFe_2xSn_3−xO₈: 0 ≤ x ≤ 1, both with ramsdellite type structure, have been synthesized by solid state reaction at 1773 and 1523 K, respectively. The relationship of the ramsdellite structure to the recently illustrated, tetragonal-packed structure is given. The Li_2+x(Li_xMg_1−xSn₃)O₈ solid solutions exhibit conductivities 4 × 10⁻⁶–5 × 10⁻⁴ (Ω cm)⁻¹ at 573 K and corresponding activation energies, 0.93−0.74 eV. The highest conductivity was observed for Li_2.3(Li_0.3Mg_0.7Sn₃)O₈, x = 0.3. In the solid solution series Li₂Mg_1−xFe_2xSn_3−xO₈, the highest conductivity was exhibited by Li₂Fe₂Sn₂O₈, 2 × 10⁻⁵ (Ω cm)⁻¹ at 573 K.     

Atoms state and interatomic interactions in perovskite-like oxides: XXXII. Formation of paramagnetic clusters in the La1−0.33x Ca0.33x Fe x Al1−x O3 and La1−0.33x Sr0.33x Fe x Al1−x O3 solid solutions

Calcium- and strontium-containing lanthanum orthoferrites have been studied using magnetic dilution method. It has been shown that the iron-atom clusters with competing ferro- and antiferromagnetic exchange interactions can exist. By using Mossbauer spectroscopy, Fe(IV) atoms have been found in the La_1?0.33x Ca_0.33x Fe_xAl_1?x O₃ solid solutions and Fe(III) atoms in two different surroundings have been found in the La_1?0.33x Sr_0.33x Fe _x Al_1?x O₃ solid solutions. The compositions of paramagnetic clusters stable at the infinite dilution have been proposed basing of the magnetic susceptibility and Mossbauer spectroscopy data.     

Electron doping versus antisite defects: Structural and magnetic properties of Sr2−xLaxCrMoO6 and Sr2−xLaxCr1+x/2Mo1−x/2O6 perovskites

This study reports the synthesis, structure and magnetic properties of Sr_2?xLa_xCrMoO₆ and Sr_2?xLa_xCr_1+x/2Mo_1?x/2O₆ samples. Although both series exhibit similar crystal structures, Sr_2?xLa_xCrMoO₆ samples present an effective electron doping revealed by a significant expansion of the unit cell with increasing x. In Sr_2?xLa_xCr_1+x/2Mo_1?x/2O₆ samples instead, the Cr-excess leads to a non electron doped system. Both series show a large amount of antisite defects whose number increases as La-content increases. Neutron diffraction patterns reveal the existence of long-range magnetic ordering for all samples but the magnetic peaks are very broad for Sr₂CrMoO₆ indicating a short coherence length of the magnetic ordering. This coherence length is increased upon replacing Sr by La. In both systems there is a clear increase of the magnetic transition temperature with increasing the La-content. The samples show ferromagnetic contributions at low temperature as deduced from the magnetic hysteresis loops typical of hard ferromagnetic materials. However, magnetic saturation is not achieved even at 5 T and the magnetic moment at this field is small. The ac magnetic susceptibility reveals the existence of several anomalies suggesting that these compounds are magnetically inhomogeneous. This is probably due to the presence of the large amount of structural defects not homogenously distributed.     

Synthesis and characterization of PrBaCo2 − x Ni x O5 + δ cathodes for intermediate temperature SOFCs

Nickel-substituted layered perovskite PrBaCo_{2 ? x} Ni _x O_{5 + δ} (PBCN) powders with various proportions of nickel (x?=?0, 0.1, 0.2, and 0.3, abbreviated as PBCN-0, PBCN-1, PBCN-2, and PBCN-3, respectively) are investigated as potential cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) based on the yttria-stabilized zirconia (YSZ) electrolyte. It is found that PBCN-1 has the highest electrical conductivity of 1,397 S cm^?1 at 400 °C. Substitution of Co by Ni decreases the thermal expansion coefficient (TEC) clearly. The average TEC at the temperature range of 35–900 °C decreases from 22.8?×?10^?6 K^?1 for PBCN-0 to 18.9?×?10^?6 K^?1 for PBCN-3. The polarization resistances of PBCN samples on YSZ electrolyte at 800 °C are 0.053, 0.048, 0.052, and 0.042 Ω cm² for PBCN-0, PBCN-1, PBCN-2, and PBCN-3, respectively. The single fuel cell with the configuration of PBCN-3/YSZ/Pt delivers the highest power densities of 100, 185, 360, 495, and 660 mW cm^?2 at 600, 650, 700, 750, and 800 °C, respectively.