Microstructure of the LaSrCuO<Subscript>4 − δ</Subscript>|Ce<Subscript>0.9</Subscript>Gd<Subscript>0.1</Subscript>O<Subscript>2 − δ</Subscript> interface and its reversibility with respect to oxygen

The conditions of formation of electrode/electrolyte interfaces LaSrCuO_{4 − δ}|Ce_0.9Gd_0.1O_{2 − δ} are optimized. It is shown that electrode layers formed by the screen printing method have better developed surfaces and are more uniform and strong as compared with thick film layers applied by a brush. Symmetric LaSrCuO_{4 − δ}|Ce_0.9Gd_0.1O_{2 − δ}|LaSrCuO_{4 − δ} cells with porous electrodes are studied by impedance spectroscopy and cyclic voltammetry in the temperature range of 773–1173 K at the oxygen partial pressure of (28–2.1) × 10⁴ Pa. The oxygen process is shown to be limited by the charge transfer across the electrode/electrolyte interface. The exchange currents are calculated in the temperature range of 773–1173 K to amount from 1 × 10⁻³ to 3.5 × 10⁻² A/cm², which points to the high reversibility of the electrode/electrolyte interface with respect to oxygen.     

Cellulose-precursor synthesis of nanocrystalline Ce<Subscript>0.8</Subscript>Gd<Subscript>0.2</Subscript>O<Subscript>2−δ</Subscript> for SOFC anodes

Developments of intermediate-temperature solid oxide fuel cells (IT SOFCs) require novel anode materials with a high electrochemical activity at 800–1070 K. The polarization of cermet anodes, made of nickel, ceria and yttria-stabilized zirconia (YSZ) and applied onto a YSZ solid electrolyte, can be significantly reduced by catalytically active ceria additions, the relative role of which increases with decreasing temperature. Further improvement is observed when using Ce_0.8Gd_0.2O_2– (CGO) having a high oxygen ionic conductivity instead of undoped ceria, owing to enlargement of the electrochemical reaction zone. Nanocrystalline CGO powders with grain sizes of 8–35 nm were thus synthesized via the cellulose-precursor technique and introduced into Ni–CGO–YSZ cermets, and tested in contact with a (La_0.9Sr_0.1)_0.98Ga_0.8Mg_0.2O_3– (LSGM) electrolyte at 873–1073 K. The results showed that the anode performance can be enhanced by additional surface activation, in particular by impregnation with a Ce-containing solution, and also by incorporation of YSZ, which probably acts as a cermet-stabilizing component. The overpotential of the surface-modified Ni–CGO (25 wt%–75 wt%) anode in a 10% H₂/90% N₂ atmosphere was approximately 110 mV at 1073 K with a current density of 200 mA/cm².Presented at the OSSEP Workshop Ionic and Mixed Conductors: Methods and Processes, Aveiro, Portugal, 10–12 April 2003     

Electrophysical properties of Ce<Subscript>0.8</Subscript>Gd<Subscript>0.2</Subscript>O<Subscript>2 − δ</Subscript> + <Emphasis Type="Italic">x</Emphasis> mol % Al<Subscript>2</Subscript>O<Subscript>3</Subscript> solid composite electrolytes

The influence of aluminum and cobalt oxides on the microstructure and the mechanical, electrical, and optical properties of the Ce_0.8Gd_0.2O_2−δ solid electrolyte was studied. Using nanosized Al₂O₃ in the synthesis allowed it to be uniformly distributed in the composite electrolyte and improved the microhardness of the resulting ceramics. The introduction of cobalt oxide made it possible to lower the synthesis temperature during the preparation of gasproof ceramics and hindered, to a certain extent, the formation of the GdAlO₃ phase during synthesis. Using the standard set of investigation methods allowed us to find solutions to several problems in using this electrolyte for solid-oxide fuel cells (SOFCs).     

Peculiarities of electrical transfer and isotopic effects H/D in the proton-conducting oxide BaZr<Subscript>0.9</Subscript>Y<Subscript>0.1</Subscript>O<Subscript>3 − δ</Subscript>

Electrical conduction of the oxide BaZr_0.9Y_0.1O_{3 − δ} is studied by electrochemical impedance spectroscopy as a function of temperature (300–600°C) and the oxygen partial pressure in gas phase saturated with H₂O or D₂O vapor. The full electrical conduction is separated into components, in particular, the bulk and grain boundary conduction. It is shown that at P _O2> 1 Pa the BaZr_0.9Y_0.1O_{3 − δ} conduction is contributed significantly by electron holes whose transference number in air atmosphere may be as high as 0.5–0.6. In reductive conditions, the electrical transfer involves proton (deuteron) charge carriers. Isotopic effect H/D in the conduction in the bulk and along the grain boundaries is determined. Isotopic effect H/D in the hole conduction is also revealed. It is shown that this effect comes out of different solubility of deuterons and protons in the oxide (the thermodynamic isotopic effect).     

Comparison of the properties of PZTNB-1 + Ni<Subscript>0.9</Subscript>Co<Subscript>0.1</Subscript>Cu<Subscript>0.1</Subscript>Fe<Subscript>1.9</Subscript>O<Subscript>4 − δ</Subscript> magnetoelectric composites manufactured from components synthesized by Sol-Gel processes

Processes were developed for manufacturing mixed magnetoelectric (ME) composites (100 − x) wt % PZTNB-1 + x wt % Ni_0.9Co_0.1Cu_0.1Fe_1.9O_{4 − δ} using sol-gel processes to synthesize piezoelectric and magnetostrictive components; these processes provide composite ceramics having different connectivity types with the same composition. When PZTNB-1 prepared by the sol-gel process is used for manufacturing the composites, there is a deep one-way doping of the piezoelectric with ferrite constituents, and this doping considerably reduces the degree of tetragonal distortion of the perovskite unit cell to the point of disappearance. In contrast, when coarse-grained PZTNB-1 powder and a ferrite nanopowder prepared by the sol-gel process are used, undesirable doping is completely inhibited. This type of composite has the highest ME transduction efficiency, by two or more times exceeding the ME ceramics of the same composition manufactured by other processes.     

Crystal structure of Bi<Subscript>36</Subscript>MgP<Subscript>2</Subscript>O<Subscript>60 − δ</Subscript>

A compound with the general formula Bi₃₆MgP₂O_{60 ? δ} was obtained by a solid-state reaction method. Its composition was confirmed using EDAX. The compound belongs to the cubic crystal system (space group I23, no. 197) and has a sillenite-type structure. The lattice parameter a _o is 10.15704(12) Å. The Rietveld refinement of the crystallographic data revealed mixed tetrahedral sites (2a) occupied by Mg, P, and Bi in a ratio of 32: 63: 5. The resulting lattice strains are compensated by vacancies in the cationic (2a) and anionic sites (24f) and by distortion of the Bi-O framework detected by IR and Raman spectroscopy.     

Effect of sintering temperature on microstructure,electric and optical properties of Ce<Subscript>0.8</Subscript>Gd<Subscript>0.2</Subscript>O<Subscript>2−δ</Subscript> + 2 mol % TiO<Subscript>2</Subscript>

The effect of the sintering temperature of the Ce_0.8Gd_0.2O_2?δ + 2 mol % TiO₂ on its microstructure, electric, and optical properties was studied using the methods of x-ray spectroscopy, scanning electron microscopy (SEM), conductivity and ellipsometry. It is shown that the electrolyte lattice parameter decreases at an increase in the sintering temperature. The pattern of the sample surface obtained using the SEM method points to the dominating role of the sintering temperature in the formation of the electrolyte microstructure. Variation of optical properties as dependent on the synthesis temperature is also determined by the microstructure parameters of ceramics: presence of pores, formation of grain interfaces.     

Synthesis and properties of high-density protonic solid electrolyte BaZr<Subscript>0.9</Subscript>Y<Subscript>0.1</Subscript>O<Subscript>3 − α</Subscript>

The described method for synthesis of proton-conducting ceramics BaZr_0.9Y_0.1O_{3 ? α} at the temperature of 1850°C from mixture of barium carbonate and zirconium-yttrium hydroxides enabled to prepare high-density translucent specimens. According to powder diffraction data, the synthesized ceramics consists of single phase and has the cubic perovskite structure with the elementary cell parameter a = 0.42009 ± 0.00004 nm. The electrophysical properties of the synthesized ceramics were measured. The conductivity of such high-density specimens was shown to excel by an order of magnitude the conductivity of porous (80% relative density) material.     

Influence of A-site deficiencies in the system La<Subscript>0.9</Subscript>Sr<Subscript>0.1</Subscript>Ga<Subscript>0.8</Subscript>Mg<Subscript>0.2</Subscript>O<Subscript>3−δ</Subscript> on structure and electrical conductivity

In this study, the A-site-deficient ABO₃ perovskites La_0.9–x Sr_0.1Ga_0.8Mg_0.2O_3– with x=0.025, 0.05, 0.075, 0.1, and 0.2 were prepared by conventional solid state reactions. X-ray investigations were carried out in order to determine the influence of the A-site deficiencies on the structure. The electrical conductivities were measured as a function of both temperature and oxygen partial pressure in ranges 500–1000 °C and 0.2–10^–6 atm, respectively. Only for small x values were single phases obtained. All compositions with A-site deficiencies exhibit a lower conductivity compared to the stoichiometric compound. It is shown by SEM micrographs that the sample morphology is changed by an A-site-deficient preparation as well. For A-site-deficient compositions, a reduction of the grain size is observed, most likely due to impurity inclusions in the grain boundaries.     

Impedance Study of the Conductivity of Solid Oxide Electrolyte Films SrZr<Subscript>0.95</Subscript>Y<Subscript>0.05</Subscript>O<Subscript>3–δ</Subscript> and CaZr<Subscript>0.9</Subscript>Y<Subscript>0.1</Subscript>O<Subscript>3–δ</Subscript>

Information on the across-plane conductivity of films of solid-oxide electrolytes SrZr_0.95Y_0.05O_3–δ and CaZr_0.9Y_0.1O_3–δ deposited on ion-conducting supports is acquired by the impedance method. It is shown that the support/film interface and the intergrain boundaries considerably affect the across-plane charge transfer in the film. The effect of the crystallographic orientation of the YSZ support on the microstructure and conductivity of the CaZr_0.9Y_0.1O_3–δ electrolyte film is demonstrated.     

The synthesis and thermodynamic properties of strontium fluoromanganite Sr<Subscript>2.5</Subscript>Mn<Subscript>6</Subscript>O<Subscript>12.5 − δ</Subscript>F<Subscript>2</Subscript>

The existence of the [SrF_0.8O_0.1]_2.5[Mn₆O₁₂] = Sr_2.5Mn₆O_{12.5 ? δ}F₂ compound was established in the SrO-Mn₂O₃-SrF₂ system at 900°C and p(O₂) = 1 atm. The crystal structure of strontium fluoromanganite was determined from the X-ray powder diffraction data, electron diffraction, and high-resolution electron microscopy. It can be described in the monoclynic system with four Miller hklm indices: hklm: H = h a* + k b* + l c ₁ ^* + m q ₁, q ₁, q ₁ = c ₂ ^* = γc ₁ ^* , γ ≈ 0.632, a ≈ a ≈ 9.72 Å, b ≈ 9.55 Å, c ₁ ≈ 2.84 Å, c ₂ ≈ 4.49 Å, monoclinic angle γ ≈ 95.6°. The electromotive force method with a solid fluorine ion electrolyte was used to refine the composition of fluoromanganite and determine the thermodynamic functions of its formation from phases neighboring in the phase diagram (SrMn₃O₆, Mn₂O₃, SrF₂, and oxygen), ΔG°, kJ/mol = ?(111.7 ± 1.9) + (89.5 ± 1.5) × 10^?3 T.     

Chemical synthesis and granulometric composition of CaZr<Subscript>0.9</Subscript>Y<Subscript>0.1</Subscript>O<Subscript>3–δ</Subscript> powders

CaZr_0.9Y_0.1O_3–δ powders were synthesized by chemical solution methods: modified Pechini method and from solutions of inorganic salts in water and ethanol. The structure crystallizes into the orthorhombic type upon annealing at 1000°C for powders prepared by the Pechini method and from solution of salts in water. It was shown that CaZr_0.9Y_0.1O_3–δ powders synthesized by various methods have different dispersities. The results obtained in a study of the granulometric composition by the sedimentation method and microscopic analysis enable fabrication of dense and mechanically strong electrolyte films and ceramics.     

Thermal analysis of the (Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>1−x</Subscript>(Y<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>x</Subscript> pigments

The synthesis of new compounds based on Bi₂O₃ is investigated because they can be used as new ecological inorganic pigments. Chemical compounds of the (Bi₂O₃)_1−x(Y₂O₃)_x type were synthesized. The host lattice of these pigments is Bi₂O₃ that is doped by Y³⁺ ions. The incorporation of doped ions provides the interesting colours and contributes to a growth of the thermal stability of these compounds. The simultaneous TG-DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments. This paper also contains the results of the pigment characterization by X-ray powder diffraction and their colour properties.     

Regime of superhigh reactivity of the YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6 + δ</Subscript> superconductor toward the components of air

Physicochemical features of the YBa₂Cu₃O_{6 + δ} superconductor synthesized via ceramic route and subjected to a kind of modification by long-term exposure to an atmosphere with low pH₂O have been studied by X-ray diffraction, thermal analysis, and magnetometry. The resulting material had a high degree of saturation with air components at room temperature and 30% humidity, up to 1.5 wt % in 30 days, which is not inherent in YBa₂Cu₃O_{6 + δ}.     

Formation of solid solutions of multiferroics in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The sequence of phases appearance during the formation of Bi_1–xNd_xFeO₃ solid solutions in powder oxides mixtures of bismuth, neodymium, and iron has been determined. It has been shown that the closeness of the reaction mixture composition to that of the individual compound (BiFeO₃ or NdFeO₃) is essential for the realization of the series of phase transformations yielding solid solutions of multiferroics Bi_1–xNd_xFeO₃ as the final product, due to the prevalence of various interphase contacts in the starting reaction zone.     

Reactivity of the oxides in the ternary V<Subscript>2</Subscript>O<Subscript>5</Subscript>-CuO-α-Sb<Subscript>2</Subscript>O<Subscript>4</Subscript> system in air

In this work it has been established which compounds finally are formed in air in the two-component CuO-V₂O₅ and CuO-α-Sb₂O₄ systems. Unknown thermal properties of CuV₂O₆, Cu₂V₂O₇ and Cu₁₁V₆O₂₆ have been established. Reactivity of the oxides and phase relations in the ternary V₂O₅-CuO-α-Sb₂O₄ system in air have been studied by using XRD and DTA methods. The results have showed the reaction of V₂O₅, CuO with α-Sb₂O₄ does not produce any compound where all the three oxides would be involved. It has been established that the α-Sb₂O₄ reacts and forms binary phases independently with CuO or V₂O₅. On the base of these results the investigated system was divided into subsidiary subsystem in which CuSb₂O₆ remains at equilibrium in the solid state with other phases formed in corresponding binary systems.     

On the Control of Plasma Parameters and Active Species Kinetics in CF<Subscript>4</Subscript> + O<Subscript>2</Subscript> + Ar Gas Mixture by CF<Subscript>4</Subscript>/O<Subscript>2</Subscript> and O<Subscript>2</Subscript>/Ar Mixing Ratios

The effects of both CF₄/O₂ and Ar/O₂ mixing ratios in three-component CF₄ + O₂ + Ar mixture on plasma parameters, densities and fluxes of active species determining the dry etching kinetics were analyzed. The investigation combined plasma diagnostics by Langmuir probes and zero-dimensional plasma modeling. It was found that the substitution of CF₄ for O₂ at constant fraction of Ar in a feed gas produces the non-monotonic change in F atom density, as it was repeatedly reported for the binary CF₄/O₂ gas mixtures. At the same time, the substitution of Ar for O₂ at constant fraction of CF₄ results in the monotonic increase in F atom density toward more oxygenated plasmas. The natures of these phenomena as well as theirs possible impacts on the etching/polymerization kinetics were discussed in details.     

Oxygen ionic and electronic transport in Gd<Subscript>2−x</Subscript>Ca<Subscript>x</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript><Subscript>−δ</Subscript> pyrochlores

Oxygen ion transference numbers for Gd_2−xCa_xTi₂O_{7 −δ} (x=0.10–0.14) pyrochlore ceramics were determined at 973–1223 K by the modified e.m.f. and faradaic efficiency techniques, taking into account electrode polarization, and from the results on oxygen permeation. The ion transference numbers vary in the range 0.95–0.98 in air, increasing when the temperature or oxygen partial pressure decreases. The activation energies for the ionic and p-type electronic transport in air are 74–77 and 87–91 kJ/mol, respectively. The p-type conductivity and oxygen permeability of Gd₂Ti₂O₇-based pyrochlores can be adequately described by relationships common for other solid electrolytes. At temperatures below 1273 K under a gradient of 10%H₂+90%N₂/air, average ion transference numbers for doped gadolinium titanate are not less than 0.97. Thermal expansion coefficients for Gd_2−xCa_xTi₂O_{7 −δ} ceramics, calculated from dilatometric data in air, are in the range (10.4–10.6)×10⁻⁶ K⁻¹ at 400–1300 K.     

The effect of the synthesis method on the morphological and luminescence characteristics of α-Zn<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript>

A promising yellow phosphor, α-Zn₂V₂O₇, was synthesized at temperatures below the phase transition temperature (610 ± 5°C) by three different methods: solid-phase and microwave processes and thermolysis of a water–salt composition. According to powder X-ray diffraction, the structures of all samples belonged to space group C/2c. Depending on the method of synthesis, the particle size varied from 500 nm (thermolysis of a water–salt composition) to 5–8 μm (ceramic and microwave methods). The excitation spectra of all samples are in the UV region (220–400 nm) and the emission spectra are in the 400–750 nm wavelength range. The photoluminescence spectra of the samples are non-elementary, which is caused by specific features of the electronic charge transfer in the structural VO₄ tetrahedra.     

Preparation and characterization of luminescent cellulose–Y<Subscript>4</Subscript>Si<Subscript>2</Subscript>O<Subscript>7</Subscript>N<Subscript>2</Subscript>:Ce<Superscript>4+</Superscript> hybrid hydrogels

Novel luminescent bio-based hydrogels comprising cellulose and Y₄Si₂O₇N₂:Ce⁴⁺ (YC) were prepared in an alkali/urea aqueous system using epichlorohydrin as a cross-linker. The structure, characteristics and properties of the hydrogels were investigated by various techniques, including FTIR spectroscopy, wideangle X-ray diffraction, scanning electron microscopy, etc. The results showed that when the content of YC was less than 0.05 g, the YC particles were tightly embedded in the macro porous of cellulose matrix, which not only supplied cavities for YC immobilization, but also supplied the pore wall to protect the structure and character of YC. Hence, the cellulose–YC hybrid hydrogels exhibited strong cyan fluorescence under a UV lamp. However, excess of YC particles were enshrouded in the cellulose matrix resulted in smaller pores, weaker fluorescence intensity, lower swelling ratio and higher mechanical properties.