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

Substitution of Ca by La in initial cubic double perovskite Ba-4(Ca2Nb2)O-11[VO](1) allowed obtaining phases with a similar structure with a lower content of structural oxygen vacancies, Ba-4(La (x) Ca2 - x Nb-2)O11 + 0.5x [VO](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 predominantly hole nature of conductivity in the high-temperature region (T > 600A degrees 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 1000A degrees C with simultaneous mass-spectrometric determination of evolved H2O and CO2. The properties of the studied Ba-4(La (x) Ca2 - x Nb-2)O11 + 0.5x (x = 0.5, 1, 1.5, 2) phases were compared with the earlier studied Ba4 - x La (x) (Ca2Nb2)O11 + 0.5x phases with similar lanthanum content.