Substitution of Ca by La in initial cubic double perovskite Ba 4(Ca2Nb2)O11[VO]1 allowed obtaining phases with a similar structure with a lower content of structural oxygen vacancies, Ba4(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 > 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 simultaneous mass-spectrometric determination of evolved H2O and CO2. The properties of the studied Ba4(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 (Ca2Nb 2)O11 + 0.5x phases with similar lanthanum content. © 2013 Pleiades Publishing, Ltd.