Nonstoichiometry, thermal expansion and oxygen permeability of SmBaCo2-xCuxO6-delta

Abstract

Phase relationship analysis in the pseudobinary SmBaCo2 - xCuxO6 - delta system at 1000-1100 degrees C in air revealed the existence of solid solutions with the layered perovskite and 123-type structures, formed within the ranges of 0 <= x <1.2 and 1.5 <= x <= 2.0, respectively. The substitution of Cu2+ for Co3+/4+ was found to induce phase transition from orthorhombic (space group Pmmm) into tetragonal (P4/mmm) polymorph at x > 0.1, and to increase oxygen deficiency studied by thermogravimetry and iodometric titration. The electrical conductivity and thermal expansion of Cu-substituted cobaltites decrease on doping, while the steady-state Oxygen permeability exhibits an opposite trend, in correlation with the oxygen content variations. The average thermal expansion coefficient of SmBaCo1.4Cu0.6O6 - delta ceramics, where the level of ionic transport is comparable to that in most permeable cobaltite-based mixed conductors, is 16.9 x 10(-6) K-1 at 25-1000 degrees C in air. At the same time, copper additions increase chemical reactivity of the materials with doped ceria electrolytes. (C) 2014 Elsevier B.V. All rights reserved.