Thermal analysis of the Ce<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Tb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> pigments

Compounds based on CeO₂ were synthesized as high-temperature environment-friendly inorganic pigments with interesting hues. The pigments have been synthesized by using the solid state reaction in the temperature range from 1,300 to 1,600 °C. The host lattice of these pigments is CeO₂ that is doped by terbium ions. The incorporation of doped ions provides interesting orange colours after application into ceramic glaze. The goal was to develop conditions for the synthesis of these compounds and to determine the influence of calcination temperature on their colouring effects. The simultaneous TG-DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments. The pigments were also evaluated from the standpoint of their structure and particle sizes.     

Sol-Gel Synthesis and Properties of Y<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Ba<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>FeO<Subscript>3</Subscript> Nanocrystals

The sol-gel method was used to prepare Y_1–xBa_xFeO₃ (x = 0, 0.05, 0.1, 0.15, 0.2) nanocrystals. The influence of the dopant content on the particle size and magnetic properties of yttrium ferrite was examined.     

High-temperature ion transport in La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>FeO<Subscript>3−δ</Subscript>

The conductivity of the entire solid solution La_1–xSr_xFeO_3–, where x=0.2, 0.4, 0.5, 0.7 and 0.9, in the oxygen partial pressure range 10^–19 to 0.5 atm and temperatures between 750 and 950 °C is reported. The analysis of the isothermal pressure dependences of the conductivity reveal that the lanthanum-strontium ferrites can be characterized as mixed ion-electron conductors in the low-oxygen pressure/high-oxygen deficiency limit. The partial contribution to conductivity from oxygen ions increases with strontium content and attains a maximal value at x=0.5. Further increase in doping results in the development of oxygen vacancy ordering phenomena and deterioration of the conducting properties.Presented at the OSSEP Workshop Ionic and Mixed Conductors: Methods and Processes, Aveiro, Portugal, 10–12 April 2003     

<Emphasis Type="Italic">T</Emphasis>–<Emphasis Type="Italic">x</Emphasis>–<Emphasis Type="Italic">y</Emphasis> Diagram of MgO–SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> System: Microstructure Design

A computer model of the T–x–y diagram of MgO–SiO₂–Al₂O₃ system is used to show the possibility of analysis of its microstructure constitution in terms of competition between primary and eutectic crystals by means of vertical mass balance diagrams calculated for a given centroid over the whole temperature range. The usefulness of horizontal mass balance diagrams is considered for studying phase relations at a fixed temperature along the chosen isopleth. Mass balances were used to determine the crystallization path at the quasi-peritectic liquidus point with the invariant reaction L + Al₂O₃ = 3Al₂O₃ · 2SiO₂ + MgO · Al₂O₃, whose composition was taken into account in giving a rationale to corundum armor element technology.     

Electrical Conductivity,Thermal Expansion and Electrochemical Properties of Perovskites PrBaFe<Subscript>2–<Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>5 + δ</Subscript>

In order to evaluate applicability of mixed-conducting PrBaFe_2–xNi _x О_{5 + δ} perovskites for cathodes of solid oxide fuel cells (SOFCs), their crystal structure, thermal and chemical expansion, electrical conductivity and electrochemical behavior were studied. The solubility limit of nickel in PrBaFe₂O_{5 + δ} corresponds to x = 0.8. At x > 0.2, the disordered cubic phase transformed into the tetragonal phase. The maximum level of conductivity (50–120 S/cm) at the operating temperatures of SOFC was found for the composition with the maximum nickel content, PrBaFe_1.2Ni_0.8О_{5 + δ}. This material is also characterized by moderate thermal and chemical expansion relative to other ferrite-nickelates. The polarization resistance of a porous PrBaFe_1.2Ni_0.8О_{5 + δ} cathode in a cell with a protective Ce_0.6La_0.4O_2–δ layer and a solid electrolyte (La_0.9Sr_0.1)_0.98Ga_0.8Mg_0.2O_3–δ was ~0.9 Ohm cm² at a temperature of 1073 K, atmospheric oxygen pressure, and current density of–120 mA cm^–2.     

Catalytic properties of Ce<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> prepared using a template in the oxidation of CO

The catalytic activity in CO oxidation of Ce _x Zr_1–x O₂ double oxides prepared using pine sawdust and cetyltrimethylammonium bromide (CTAB) as templates is compared. It is found by means of SEM and the low-temperature adsorption of N₂ that biomorphic oxides reproduce the macropore structure of the template. It is shown via XRD and Raman spectroscopy that all samples contained mixed ceria-zirconia oxide. The double oxides form a cubic phase with a lattice of the fluorite type at a ratio of Ce: Zr = 4, regardless of the nature of the template; when Ce: Zr = 1, the biomorphic mixed oxide forms a tetragonal phase. According to Raman spectroscopy and XRD it was shown that the distortion of the oxygen sublattice is higher in biomorphic samples. Energy dispersive analysis shows that Ca impurities were present in the biomorphic samples, introducing additional distortions in the lattice of double oxide and leading to the formation of anionic vacancies. It is found that when Ce: Zr = 4, the conversion of CO on biomorphic oxide in the range of 100–350°C is higher than that observed for Ce _x Zr_1–x O₂ (CTAB); reducing the Ce: Zr ratio in the biomorphic sample to 1 results in a marked decrease in CO conversion at 100–200°C. It is concluded that these differences are due to changes in the mobility of the lattice oxygen.     

Oxygen transport in La<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>Co<Subscript>1−<Emphasis Type="Italic">y</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>O<Subscript>3−δ</Subscript>

The surface exchange coefficient and chemical diffusion coefficient of oxygen for the perovskites La_0.6Sr_0.4Co_1–yFe_yO_3– (y=0.2, 0.5 and 0.8) were measured using the conductivity relaxation technique. Measurements were performed between 600 and 800 °C in an oxygen partial pressure range between 10^–4 and 1 bar. Both transport coefficients decrease markedly with decreasing oxygen partial pressure below about 10^–2 bar at all temperatures. This is attributed to ordering of oxygen vacancies. Implications for using La_0.6Sr_0.4Co_1–yFe_yO_3– as an oxygen separation membrane are discussed.Presented at the OSSEP Workshop Ionic and Mixed Conductors: Methods and Processes, Aveiro, Portugal, 10-12 April 2003     

Synthesis and electrochemical evaluation of La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript> catalysts for zinc-air batteries

La_1-x Sr _x MnO₃ (x?=?0.1～0.4) catalysts for primary and rechargeable zinc-air batteries have been successfully synthesized by the citrate method and their electrochemical properties measured. The materials can catalyze both ORR and OER, and the one with ideal composition of La_0.8Sr_0.2MnO₃ catalyst exhibits the highest catalytic activity and durability in alkaline medium. The resulting primary zinc-air cell shows a peak power density of 146 mW cm^?2 at 235 mA cm^?2. The secondary cell exhibits a charge-discharge voltage gap of 1.0 V at 10 mA cm^?2, which is highly stable over many charge-discharge cycles.     

Synthesis,structure, and properties of substituted bismuth niobates Bi<Subscript>3</Subscript>Nb<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Er<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>7–δ</Subscript>

Results are reported of a study of the structural and electrical characteristics of substituted bismuth niobates with composition Bi₃Nb_1–x Er _x O_7–δ, which are promising oxygen-ion conductors. The homogeneity regions of solid solutions were determined by X-ray phase analysis and electron microscopy with X-ray fluorescence microanalysis, and their crystal-chemical parameters were calculated. The electrical conductivity of sintered samples was examined by impedance spectroscopy.     

Electrotransport Properties of Ceramics Based on Bi<Subscript>4</Subscript>V<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>x</Subscript>O<Subscript>11 − <Emphasis Type="Italic">x</Emphasis></Subscript>

Conditions for the formation of single-phase compounds in the synthesis of solid solutions Bi₄V_{2 − x} Fe_xO_{11 − x} are studied. The sequence of phase transitions is determined. Parameters of unit cells of solid solutions are determined. The net conductance as a function of temperature and composition is studied.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 607–609.Original Russian Text Copyright © 2005 by Emel’yanova, Buyanova, Zhukovskii.     

Anodic Electrocatalysts for Fuel Cells Based on Pt/Ti<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Ru<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript>

The electrocatalytic activity of materials in the 10% Pt/Ti_1–xRu _x O_2–δ system, where x = 0–0.3 (0 ≤ Ru ≤ 30 mol %), in the reactions of hydrogen electrooxidation in the presence of CO is studied in the liquid three-electrode cell and a model of fuel cell. It is shown that the tolerance of the electrocatalysts towards CO is determined by the crystal structure of the support: the support with the rutile structure provides a higher rate of CO desorption than the support with the anatase structure. The potential of the onset of CO oxidation decreases with increasing concentration of dopant in the support from 650 mV for 10% Pt/TiO₂ to 480 mV (NHE) for 10% Pt/Ti_0.91Ru_0.09O_2–δ (rutile). The use of these materials as the anodic catalysts of fuel cell operating with hydrogen containing 30 ppm CO enabled us to obtain a current density by 7 times higher as compared with the 20% PtRu/C E-Tec catalysts.     

Potassium–conducting K<Subscript>1 − 2<Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>GaO<Subscript>2</Subscript> solid electrolytes

Solid electrolytes with potassium-cation conductivity in the K_{1 − 2x} Pb _x GaO₂ system were synthesized and studied. It was found that solid solutions based on potassium monogallate are formed in a wide range of compositions. They contain vacancies in the potassium sublattice that provide for high conductivity of electrolytes. The relationship is considered between electric characteristics of solid electrolytes and the composition and structure of solid solutions. The results are compared to the earlier obtained data for similar solid electrolytes based on potassium monoaluminate and monoferrite.     

Production and characteristics of substituted lanthanum niobate LaNb<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>W<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>4 + δ</Subscript>

Solid solutions LaNb_1–x W _x O_{4 + δ} (x = 0.02–0.10, Δx = 0.02) were investigated, which crystallize in the monoclinic system (space group I2/c) at room temperature and undergo a phase transition into the tetragonal modification with increasing temperature. The stability of various modifications was analyzed by high-temperature X-ray powder diffraction analysis. The electrical conductivity of sintered samples was studied by impedance spectroscopy. Insertion of tungsten into the niobium sublattice leads to an increase in the conductivity of the solid solutions.     

Electrochemical characterization of praseodymium centers in Pr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> zirconias using electrocatalysis and photoelectrocatalysis

The voltammetry of nanoparticles and scanning electrochemical microscopy are applied to characterize praseodymium centers in tetragonal and monoclinic zirconias, doped with praseodymium ions (Pr _x Zr_1−x O₂), prepared via sol–gel routes. Doped zirconia nanoparticles were synthesized by a sol–gel liquid-phase route and characterized by different techniques, including X-ray diffraction powder pattern, ultraviolet–visible diffuse reflectance spectroscopy, infrared spectroscopy, and transmission electron microscopy (TEM). Gels annealed at around 400 °C yielded tetragonal Pr _x Zr_1−x O₂ phases. The monoclinic forms of Pr-doped ZrO₂ were obtained by annealing at temperatures higher than 1,100 °C. TEM micrographs proved that the size of the nanoparticles produced was dependent on their crystalline form, around 15 and 60 nm for tetragonal and monoclinic, respectively. The electrochemical study confirmed that a relatively high content of praseodymium cation was in the chemical state (IV), i.e., as Pr⁴⁺, in both zirconia host lattices. The catalytic and photocatalytic effects of Pr⁴⁺ centers located in the monoclinic zirconia lattice on nitrite reduction and oxygen evolution reaction were studied.     

Preparation of mesoporous Ce<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> mixed oxides and their catalytic properties in methane combustion

Mesoporous Ce_{1 ? x} Fe _x O₂ mixed oxide catalysts of different molar ratios (x = 0.1–0.5) were prepared by the citric acid sol-gel method and the microwave technique. The activities of Ce_{1 ? x} Fe _x O₂ mixed oxides on methane combustion were investigated, and the structure and reductive properties were characterized by XRD, BET, DRS, and TPR. The data showed that Ce_{1 ? x} Fe _x O₂ mixed oxides prepared were mesoporous material. When x ≤ 0.2, the transition metal Fe incorporated into the lattice of CeO₂ to form cubic Ce_{1 ? x} Fe _x O₂ solid solutions, and mixed phases of cubic Ce_{1 ? x} Fe _x O₂ solid solutions and α-Fe₂O₃ existed when x > 0.2. Ce_{1 ? x} Fe _x O₂ solid solutions show higher activity for methane combustion than pure CeO₂, especially for Ce_0.9Fe_0.1O₂.     

Transport and thermal characteristics of Cs<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Rb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>H<Subscript>2</Subscript>PO<Subscript>4</Subscript>

The transport and thermal properties of Cs_{1 − x} Rb _x H₂PO₄ in a wide range of compositions were studied. The binary salts Cs_{1 − x} Rb _x H₂PO₄ (x = 0–0.9) contain solid solutions with a structure of CsH₂PO₄. The binary salts were synthesized by mechanically mixing the starting components and growing crystals by isothermal evaporation from aqueous solutions. The properties of Cs_{1 − x} Rb _x H₂PO₄ salts obtained by different procedures were found to differ considerably. At higher rubidium contents in compounds obtained by mechanical mixing, the superionic transition temperature rose insignificantly, the high-temperature phase conductivity decreased twofold, the low-temperature conductivity increased within the limits of the order of magnitude, and the system of hydrogen bonds was slightly weakened. In Cs_{1 − x} Rb _x H₂PO₄ crystals grown from solutions, the temperature of the superionic transition decreased along with its slowing down, and the low-temperature conductivity increased by more than three orders of magnitude because of the higher contents of residual acid aqueous centers in the structure of the salt. These systems are characterized by increased thermal stability.     

The synthesis and transport properties of the cuprates La<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript>1 + <Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>2</Subscript>O<Subscript>6 + δ</Subscript>

The cuprates La_{2 ? x} Sr_{1 + x} Cu₂O_{6 + δ}(x = 0, 0.1, 0.2) are synthesized by solid-state method. Their dc conductivity was studied over the 373 to 1173 K temperature range and 10 to 2.1 × 10⁴ Pa oxygen partial pressure range by using four-probe technique. It is shown that the cuprate conductivity in air is maximal at ～673 K; it is 60 S/cm for La₂SrCu₂O_6.09; 68 S/cm, for La_1.9Sr_1.1Cu₂O_6.18; and 81 S/cm, for La_1.8Sr_1.2Cu₂O_6.10. The thermal expansion coefficient of La₂SrCu₂O_6.09 is determined by thermomechanical method and high-temperature X-ray diffraction method; its value (16 ppm K^?1) shows that the material is compatible with the ceria-based solid electrolytes during the thermal cycling.     

Transport and structural properties of compounds (1 − <Emphasis Type="Italic">x</Emphasis>)CsHSO<Subscript>4</Subscript>-<Emphasis Type="Italic">x</Emphasis>KH<Subscript>2</Subscript>PO<Subscript>4</Subscript>

The homogeneous substitution of cations (K⁺) and anions (H₂PO₄⁻) for CsHSO₄ is performed. The dependences of protonic conductivity and structure of (1 − x)CsHSO₄-xKH₂PO₄ (x = 0.05–0.9) compounds on the composition are studied. It is found that the introduction of KH₂PO₄ leads to the formation of a new highly conductive phase. At small amounts of introduced KH₂PO₄ (x = 0.05), a mixed salt forms; its low-temperature conductivity is by more than two orders of magnitude higher than that of the source salts. The thermal behavior of mixed salt (1 − x)CsHSO₄-xKH₂PO₄ of various compositions and the peculiarities of crystal structure are studied. The structural parameters of the salt at x = 0.05–0.5 are close to those of Cs₃(HSO₄)₂(H₂PO₄). At higher x, another phase forms, whose structure has yet to be determined. The thermal stability of the salt decreases with increasing fraction of KH₂PO₄ introduced. The conductivity of the composites based on the mixed salt and silicon dioxide (1 − y){xKH₂PO₄-(1 − x)CsHSO₄}-ySiO₂ (x = 0.05, 0.1; y = 0.1–0.7) is studied. It is shown that, in the low-temperature range, the conductivity of composite systems increases within an order of magnitude, passes through a maximum, and, then, decreases at y > 0.5 due to the percolation effect.     

Synthesis of (Ni<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>P (0 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 0.65) substitution solid solution

The phosphides (Ni_{1 ? x} Co _x )₂P (0 ≤ x ≤ 0.65) crystallizing in the hexagonal system, space group P \(\bar 6\)2m, were synthesized in two steps starting from the continuous solid solution (Ni_{1 ? x} Co _x )₃(PO₄)₂ · 8H₂O. The initial phosphates were first completely dehydrated at 800°C and then reduced with hydrogen at 900–1000°C for 1–2 h.