The influence of temperature and procedure on the phase relationships of LaxBa1-xCoO3-delta with 0 <= x <= 1.0, oxygen nonstoichiometry, thermal and chemical expansion contributions, in air, and the electrochemical response of electrodes formed by three porous layers LaxBa1-xCoO3-delta /(50:50wt%) LaxBa1-xCoO3-delta+Ce0.9Gd0.1O1.95/Ce0.9Gd0.1O1.95 have been investigated. The crystal structures of samples with 0 <= x <= 0.5 and x = 1.0 were refined satisfactorily with a single phase. The cubic perovskite could be obtained for the x = 0.5-0.7 furnace-cooled samples (similar to 5 degrees C/min). This phase was found unstable for x = 0.6 and 0.7, in air, at T <= 1000 degrees C. For x = 0.8 and 0.9 a mixture of phases has been obtained. The expansion coefficient reaches a maximum of 26x10(-6) K-1 for x = 0.6 and a minimum of 16x10(-6) K-1 for x = 0.8 and 0.9 for Delta T = 20-900 degrees C. AC impedance spectroscopy measurements were carried out in the temperature range of 400 <= T <= 700 degrees C. A minimum polarization resistance Rp similar to 0.065-0.075 ohm cm(2) was obtained for 0.4 <= x <= 0.7 at T = 600 degrees C, which compares very well with the Rp value reported for composites prepared with cobaltites. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.043201jes]