SYNTHESIS AND PHASE ANALYSIS OF FLUORINE-DOPED PEROVSKITES BASED ON BARIUM-CALCIUM NIOBATES

The paper takes into account the fact that today, as a material for the electrolyte of solid oxide fuel cells, the compounds with a perovskite-like structure characterized by oxygen-ion conductivity in the dry air and proton conductivity in the air atmosphere are actively studied. The possibility of proton defects in these compounds is due to the presence of oxygen vacancies. The presence of vacant positions in the oxygen sublattice promotes reversible dissociative absorption of water from the gas phase and the appearance of proton conductivity. An example of a phase characterized by a perovskite structure and having an oxygen deficiency in the anion sublattice is barium-calcium niobate Ba₂CaNbO_5,5 described in the literature as an oxygen-ion and proton conductor. Isovalent and heterovalent doping of cationic sublattices is the one of methods of modification of this type structure and optimization of physicochemical properties of complex oxide materials. However, the development of anionic doping can be an alternative for the obtaining of new materials with improved properties. It was established that the anionic substitution F ⁻→O ²⁻ leads to increase in oxygen and proton conductivities under small fluorine concentration (a mixed anion effect). The present research is an extension of the study of the effect of heterovalent anionic doping on oxygen-ion and proton transport. In this paper, the fluorine-doped complex oxides based on barium-calcium niobate Ba_2-0,5xCaNbO₅,_5-xF_x were obtained, X-ray analysis was performed. The phases were made by the anionic doping of oxygen sublattice of niobate barium-calcium Ba₂CaNbO_5,5  by fluorine ions. The synthesis was carried out by a solidphase method, the maximum annealing temperature was 1300^оС. All the samples (0 < х ≤ 0,4) were single-phase and characterized by the cubic structure of a double perovskite. It has been established that the introduction of ions with a smaller radius (F^- ) leads to a decrease of the lattice parameter of the fluorine-substituted compositions compared with the undoped barium-calcium niobate Ba₂CaNbO_{5,5 .}

1. Thangadurai V., W. Weppner Recent progress in solid oxide and lithium ion conducting electrolytes research. Ionics, 2006;12:81−92 (in Eng.).

2. Tarancón A. Strategies for Lowering Solid Oxide Fuel Cells Operating Temperature. Energies, 2009;2:1130−1150 (in Eng.).

3. Gallasso F., Darby W. Ordering of the octahedrally coordinated cation position in the perovskite structure. J. Phys. Chem., 1963;67(1):131−133 (in Eng.).

4. Bananos N. Oxide-based protonic conductors: point defects and transport properties. Solid State Ionics, 2001;145:265−274 (in Eng.).

5. Du Y., Nowick A.S. Structural transitions and proton conduction on nonstoichiometric A3B'B"2O9 perovskite-type oxides. J. Am. Ceram Soc., 1995;78(11)3033−3039 (in Eng.).

6. Animitsa I.E., Neiman A.Ya., Kochetova N.A., Korona D.V. Intraphase chemical diffusion of water in Ba4Ca2Nb2O11. Russian J. of Electrochemistry, 2006;42:311−319 (in Eng.).

7. Korona D.V., Neiman A.Ya., Animitsa I.E., Sharafutdinov A.R. Effect of humidity on conductivity of Ba4Ca2Nb2O11 phase and solid solutions based on this phase. Russian J. of Electrochemistry, 2009;45:586−592 (in Eng.).

8. Animitsa I., Tarasova N., Filinkova Ya. Electrical properties of the fluorine-doped Ba2In2O5. Solid State Ionics, 2012;207:29−37 (in Eng.).

9. Tarasova N., Filinkova Ya., Animitsa I. Hydration and forms of oxygen-hydrogen groups in oxyfluorides Ba2-0.5xIn2O5-xFx. Russian J. of Physical Chemistry A, 2012;86:1208−1211 (in Eng.).

10. TarasovaN., Animitsa I. Novel proton-conducting oxyfluorides Ba4-0.5xIn2Zr2O11-xFx with perovskite structure. Solid State Ionics, 2012;264:69−75 (in Eng.).

11. Tarasova N., Filinkova Ya., Animitsa I. Electric properties of oxyfluorides Ba2In2O5-0.5xFx with brownmillerite structure, Russian J. of Electrochemistry, 2013;49:45−51 (in Eng.).

12. Tarasova N., Animitsa I. Effect of anion doping on mobility of ionic charge carriers in solid solutions based on Ba2In2O5. Russian J. of Electrochemistry, 2013;49:698−703 (in Eng.).

13. Tarasova N.A., Zhuravlev N.A., Animitsa I.E., Denisova T.A., Baklanova Ya.V., Kavun V.Ya. Features of the Local Structure of Hydrated Fluorine-Substituted Solid Solutions Based on Ba2In2O5. Bulletin of the Russian Academy of Sciences. Physics, 2014;78:730–732 (in Eng.).

14. Tarasova N., Animitsa I., Denisova T., Nevmyvako R. The influence of fluorine doping on short-range structure in brownmillerite Ba1.95In2O4.9F0.1. Solid State Ionics, 2015;275:47−53 (in Eng.).

15. Tarasova N.A., Animitsa I.E. Hydration processes of oxyfluorides Ba2+0.5хIn2O5Fх (Protsessy gidratatsii oksiftoridov Ba2+0.5хIn2O5Fх). Inorganic Materials: Applied Research, 2015;(8): 50–56 (in Russ.)

16. Animitsa I.E., Tarasova N.A., Denisova T.A., Baklanova Ya.V. Proton state in hydrated fluoro-substituted brownmillerites Ba2In2O5-0.5xFy ·nH2O. Journal of Structural Chemistry, 2016;57:910−916 (in Eng.).

17. Tarasova N.A., Pilshchikova E.D., Obrubova A.V., Korona D.V. The hydration processes of and nature of protons in novel chlorine-substituted brownmillerites Ba2-0.5xIn2O5-xClx (Protsessy gidratatsii i priroda protonov v novykh khlorzameshchennykh braunmilleritakh Ba2-0.5xIn2O5-xClx). International Scientific

18. Tarasova N.A., Animitsa I.E., Pilshchikova E.D., Obrubova A.V. Influence of the nature of substituent ion (F- , Cl- ) on transport properties of brownmillerites based on barium indate (Vliyanie prirody iona-zamestitelya (F-, Cl-) na elektroprovodnost' braunmilleritov na osnove indata bariya). International Scientific Journal for Alternative Energy and Ecology (ISJAEE), 2016;(7−8):38–42 (in Russ.)

19. Tarasova N.A., Pilshchikova E.D., Galisheva A.O., Baldina L.I. Influence of anionic heterovalent doping on the nature of electroconductivity and chemical stability of Ba2In2O5 (Vliyanie anionnogo geterovalentnogo zameshcheniya na prirodu elektroprovodnosti i khimicheskuyu stabil'nost' Ba2In2O5). International Scientific Journal for Alternative Energy and Ecology (ISJAEE), 2016;(21−22):25–30 (in Russ.).

20. Shannon R.D. Ionic Radii. ActaCrystallographica, 1976;A32:155−169 (in Eng.).