Vol 53, No 8 (2017)

Structural features of solid solutions based on CaYb₂S₄ (the Yb₃S₄ structural type) are studied using the methods of Rietveld full-profile analysis, measurement of pycnometric density, and thermal analysis in vacuum with simultaneous study of variation of the elementary cell parameters. Conductivity of samples with different doping additive content are studied in the medium of argon and in the hydrogen sulfidecontaining medium using the impedance technique. Different mechanisms of defect formation are analyzed as dependent on the doping degree.

The structural and electric characteristics of fluorine-substituted complex oxides obtained by anion doping based on Ba₂CaNbO_5.5 and Ba₂In₂O₅ matrices were compared. The mobility of ion charge carriers was found to depend on the concentration of the dopant anion and oxygen vacancies and the degree of disordering of the latter.

This work is devoted to the studying of effects of La₂NiO₄ doping with alkaline-earth elements: Ca, Sr, and Ba (at an amount of 15 mol %) on its structural, electrical, and electrochemical properties. The effects of the alkaline-earth element nature, introduction of the Ce_0.8Sm_0.2O_1.9-electrolyte (SDC) component to the functional layer, and the presence of collecting film onto electrochemical activity of the electrodes contacting the Ce_0.8Sm_0.2O_1.9-electrolyte are examined. The doping was found to increase the La2NiO4 full conductivity due to increase in the hole conductivity. The maximal conductivity (at the sample density of 86–89%) was obtained for the Ca-doped composition: 85 S/сm at 700°C, as compared with 65 S/сm for undoped La₂NiO₄. at the same time, the doping was found to deteriorate the electrodes’ electrochemical activity which is likely to be due to loss of interstitial oxygen as a result of the doping. The using of composite electrodes allows increasing polarization conductivity markedly. For instance, at 700°С the conductivity of La₂NiO₄ is 0.25 S/сm²; of its based composite, 0.67 S/сm².

The kinetics of oxygen isotope exchange between gas-phase oxygen and the electrochemical cell O₂, Pt | ZrO₂ + 10 mol % Y₂O₃ (YSZ) | Pt, O₂ with applied potential difference (ΔU = ±1.2 V) is studied in the temperature range of 600–800°С and the oxygen pressure interval of 3–13 kPa. An original design of a vacuum electrochemical cell with the separated gas space is put forward for studying how the potential difference on the electrochemical cell influences the kinetics of interaction of gas-phase oxygen with the gas electrode O₂, Pt | YSZ in the electrochemical cell. It is shown that the oxygen interphase exchange rate is the higher the more negative the charge on the electrode studied; moreover, the mechanism of gas-phase oxygen exchange with the gas electrode O₂, Pt | YSZ in the electrochemical cell depends fundamentally on the electrode charge sign. The possible reasons for the revealed differences are discussed; the corresponding models are proposed.

Substituted lanthanum manganites with the general composition La_1–xBi_xMn_1–yFe(Ni,Cu)yO_{3 + δ} and unit cells in rhombohedral (space group (sp. gr.) R-3c) and/or orthorhombic (sp. gr. Pnma) symmetry are synthesized and attested. They are characterized by permanent excessive oxygen nonstoichiometry within a single structure type at room temperature, independent of the dopant concentration. These materials are adequately mechanically compatible with bismuth niobates. The interval of their chemical compatibility with bismuth-containing compounds is limited by 700–800°C. In this region, the conductivity of composites of substituted lanthanum manganites and bismuth-containing electrolytes is higher as compared with individual compounds. The use of individual manganites or their composites as the electrodes in cells with bismuthcontaining electrolytes increases the total conductivity of the cells.

Lithium-containing bismuth titanates with the pyrochlore-type structure Bi_1.6Li_xTi₂O_7–δ were obtained for the first time. The formation of the pyrochlore phase was confirmed by X-ray diffraction analysis, scanning electron microscopy and local microanalysis. In Bi_1.6M_xTi₂O_7–δ, the lithium and indium are occupied the bismuth sites, primarily. The electrophysical properties of doped bismuth titanates were studied by impedance spectroscopy in the frequency range 1–10⁶ Hz. In the low-temperature range (of up to ~400°C), electron conductivity predominates; above 400°C, the oxygen-ion type of conductivity is revealed. In the range p(O₂) = 0.21–1 atm, the average value of the sum of ion transport numbers is 0.5 at 500–550°C. The relaxation process was found from the frequency dependences of the dielectric parameters (ε', tan δ, M''), which was of the same type for systems with different dopants (In, Li) probably due to the hopping mechanism of oxygen conductivity.

The ion conductivity of the salts [(C₄H₉)₄N]BF₄ and [(C₄H₉)₄N]Br was studied in vacuum at temperatures from room temperature to 190 and 135°C, respectively. The salts have phase transitions to disordered high-temperature phases accompanied by an increase in conductivity. [(C₄H₉)₄N]Br has higher conductivity than [(C₄H₉)₄N]BF₄. As the conductivity decreases with the increasing size of the anion, the BF₄^– and Br^– anions are the most probable current carriers in the salts.