High temperature transport properties of La0.5-xPrxBa0.5CoO3-δ perovskite (x=0, 0.2, 0.5)

LnBaCo(2)O(6-delta) (Ln = lanthanide) are prospective materials for oxygen separation membranes. These materials show high rates of oxygen surface exchange and diffusivity, and high electrical conductivity. In this work, the La0.5-xPrxBa0.5CoO3-delta system (0 <= x <= 0.50) was studied as potential oxygen separation membrane. Samples were synthesized via a combined EDTA-citrate complexing sol-gel process at 1100 degrees C in air. Dense samples were obtained after 6 h calcination at 1100 degrees C in air. Single cubic perovskite phase (S.G. Pm (3) over barm) was obtained for 0 <= x <= 0.25, and tetragonal (S.G. P4/mmm) double perovskite phase for 0.30 <= x <= 0.50. Electrical conductivity (sigma) was measured as a function of temperature for La0.5Ba0.5CoO3-delta (La50), La0.3Pr0.2Ba0.5CoO3-delta (La30) and Pr0.5Ba0.5CoO3-delta (La00) compounds. All the compounds have shown high electrical conductivity, reaching values between 1000 and 2000 Scm(-1) at 300 degrees C. On increasing temperature above 300 degrees C, the conductivity decreases, exhibiting a metallic-like behavior, taking values of sigma = 547, 385 and 714 Scm(-1) at 800 degrees C, for La00, La30 and La50, respectively. Oxygen permeation measurements were carried out as a function of temperature between 700 and 900 degrees C by varying the He flux between 1 and 100 ml center dot min -1 on dense membranes of the same thickness (L = 1.4 mm). Ionic conductivities of 0.037, 0.054 and 0.014 Scm(-1) were estimated from the oxygen permeation flux at 800 degrees C for La00, La30 and La50, respectively.