Effect of Nb5 + content on the high temperature properties of the mixed conductors system La1 − xBaxCo1 − yNbyO3 − δ with 0.6 ≤ x ≤ 1.0 and 0 ≤ y ≤ 0.4

Abstract

The replacement of Co by Nb in the La1 − xBaxCo1 − yNbyO3 − δ (0.6 ≤ x ≤ 1.0) system and its effects on phase stability and high temperature properties of the cubic perovskite phase were investigated by X-ray diffraction, dilatometry, electrical conductivity, oxygen permeation and electrochemical impedance spectroscopy. The incorporation of Nb in the B site stabilizes the cubic perovskite in the as prepared samples. The Nb solubility increases from y = 0.1, for the sample with Ba content x = 0.6, to y = 0.4 for 0.8 ≤ x ≤ 1.0. However, after a heat treatment at 750 °C during 10 days small amounts of secondary phases were detected for samples with x = 0.9 and 1.0. The linear expansion of the cubic phases decreases with the Nb content as well as with the Ba content. The minimum value, α = 12.9 × 10− 6 K− 1, was obtained for La0.2Ba0.8Co0.6Nb0.4O3 − δ. The behavior of electrical conductivity and oxygen permeation data with Nb content is explained from variations in the oxygen vacancy concentration, which is controlled by Nb5 + and Ba2 + contents. The minimum polarization resistance value, Rp = 0.08 Ω cm2, was obtained at 600 °C for La0.2Ba0.8Co0.9Nb0.1O3 − δ. The low Rp value of this compound and the crystal structure stability of various compositions in the system La1 − xBaxCo1 − yNbyO3 − δ with x ≥ 0.7 and y ≥ 0.1 make these materials of interest as mixed conductors.