Effect of hydration on conductivity of Ba4La x Ca2 − x Nb2O11 + 0.5x (x = 0.5, 1, 1.5, 2) phases

Abstract

Abstract-Substitution of Ca by La in initial cubic double perovskite Ba 4 (Ca 2 Nb 2 )O 11 [V O ] 1 allowed obtaining phases with a similar structure with a lower content of structural oxygen vacancies, Ba 4 (La x Ca 2 -x Nb 2 )O 11 + 0.5x [V O ] 1 -0.5x (x = 0.5, 1, 1.5, 2). The impedance technique was used to measure the temperature dependences of conductivity in the atmosphere of dry and humid air. Transport numbers determined using the EMF method in an oxygen-air and water steam concentration cells point to the pre dominantly hole nature of conductivity in the high temperature region (T > 600°C) and to predominance of proton conductivity in the low temperature region. Activation energies of hole and proton conductivity were calculated. Thermogravimetric measurements were carried out under heating from 25 to 1000°C with simul taneous mass-spectrometric determination of evolved H 2 O and CO 2 . The properties of the studied Ba 4 (La x Ca 2 -x Nb 2 )O 11 + 0.5x (x = 0.5, 1, 1.5, 2) phases were compared with the earlier studied Ba 4 ⎯ x La x (Ca 2 Nb 2 )O 11 + 0.5x phases with similar lanthanum content.

Novel anion conductors – conductivity, thermodynamic stability and hydration of anion-substituted mayenite-type cage compounds C12A7:X (X = O, OH, Cl, F, CN, S, N)

“…The hydration of perovskite-based materials turned out to be a real bulk process with the chemical diffusion of H 2 O into the entire volume. [58][59][60][61] In fluorite-type oxides (Zirconia, Ceria), hydration appears to be more of a surface-interface process inside grain boundaries. 62,63 Kim et al did not observe any significant effect on the conductivity of nano-crystalline ceria in hydration experiments.…”