ISSN 1070-4272, Russian Journal of Applied Chemistry, 2018, Vol. 91, No. 5, pp. 770−777. © Pleiades Publishing, Ltd., 2018. Original Russian Text © A.V. Kas’yanova, Yu.G. Lyagaeva, N.A. Danilov, S.V. Plaksin, A.S. Farlenkov, D.A. Medvedev, A.K. Demin, 2018, published in Zhurnal Prikladnoi Khimii, 2018, Vol. 91, No. 5, pp. 656−663.
APPLIED ELECTROCHEMISTRY AND METAL CORROSION PROTECTION
Ceramic and Transport Characteristics of Electrolytes Based on Mg-Doped LaYO3 A. V. Kas’yanovaa,b, Yu. G. Lyagaevaa,b,*, N. A. Danilova,b, S. V. Plaksina, A. S. Farlenkova,b, D. A. Medvedeva,b, and A. K. Demina,b a
Institute of High-Temperature Electrochemistry, Ural Branch, Russian Academy of Sciences, Yekaterinburg, 620137 Russia b Ural Federal University named after the first president of Russia B.N. Yeltsin, Yekaterinburg, 620075 Russia *e-mail:
[email protected] Received April 13, 2018
Abstract—Effect of magnesium on the sinterability, phase composition, microstructure, and transport properties of proton-conducting materials of composition LaY1–xMgxO3–δ (х = 0, 0.05, 0.1) was studied. Ceramic samples were obtained by using the citrate-nitrate synthesis method at various sintering temperatures (1250–1400°C). It was shown that, for the samples with x = 0.05 and 0.1, the relative density was no less than 95% at a sintering temperature of 1350°C, whereas undoped lanthanum nitrate has this density at 1450°C. An X-ray diffraction analysis and scanning electron microscopy demonstrated that introduction of a small amount of magnesium (x = 0.05) is sufficient for forming the single-phase and high-dense ceramics. Electrical conductivity data show that the LaY0.95Mg0.05O3–δ sample has high overall and ionic conductivities. DOI: 10.1134/S1070427218050075
High-temperature proton-conducting electrolytes form a unique class of oxide materials that can exhibit oxygen-ion conductivity in air and proton conductivity in humid air or hydrogen. This circumstance enables their application as the main functional elements in a wide variety of electrochemical devices, including fuel cells, electrolyzers, sensors, and membrane reactors [1–5]. However, the working conditions of the majority of solid-oxide electrochemical devices are high temperatures and aggressive atmospheres (H2, CO, hydrocarbons, synthesis gas, and biomass fuel). Therefore, a number of requirements are imposed on the electrolytes: high ionic and low electronic conductivity, chemical stability, and chemical and thermal compatibility with other functional components [6–8]. Of particular interest among the wide variety of proton-conducting materials are those containing no alkaline-earth elements. This is due to their high chemical stability toward reactions in which hydroxides and carbonates are formed. To electrolytes of this kind
belong lanthanum orthoniobates (LaNbO4), lanthanum orthophosphates (LaPO 4 ), lanthanum tungstates (La xWO 3+1.5x) and oxides ABO 3 with a perovskite structure, in which the A and B sublattices are occupied by trivalent cations (e.g., LaYO3) [9–15]. Materials based on lanthanum yttrate can be considered as an alternative to the best studied proton-conducting electrolytes based on cerates and zirconates: due not their excellent chemical as well as wide electrolytic region in which predominantly proton conductivity prevails [16–21]. It is noteworthy that LaYO3 has two polymorphic modifications: lowand high-temperature. The low-temperature form has an orthorhombic structure of the perovskite type below 1450°C. The transition to the high-temperature form with a monoclinic structure occurs upon annealing above 1450°C [22, 23]. Strontium-doped lanthanum yttrate La0.9Sr0.1YO3–δ has a higher electrical conductivity than other acceptordoped LaYO3 [24, 25], because the substitution of La3+ with strontium gives rise to oxygen vacancies responsible 770
