Abstract
The effect of the A-site cation ordering on the chemical stability, oxygen stoichiometry and electrical conductivity in layered LaBaCo2O5+δ double perovskite was studied as a function of temperature and partial pressure of oxygen. Tetragonal A-site cation ordered layered LaBaCo2O5+δ double perovskite was obtained by annealing cubic A-site cation disordered La0.5Ba0.5CoO3-δ perovskite at 1100 °C in N2. High temperature X-ray diffraction between room temperature (RT) and 800 °C revealed that LaBaCo2O5+δ remains tetragonal during heating in oxidizing atmosphere, but goes through two phase transitions in N2 and between 450 °C and 675 °C from tetragonal P4/mmm to orthorhombic Pmmm and back to P4/mmm due to oxygen vacancy ordering followed by disordering of the oxygen vacancies. An anisotropic chemical and thermal expansion of LaBaCo2O5+δ was demonstrated. La0.5Ba0.5CoO3-δ remained cubic at the studied temperature irrespective of partial pressure of oxygen. LaBaCo2O5+δ is metastable with respect to La0.5Ba0.5CoO3-δ at oxidizing conditions inferred from the thermal evolution of the oxygen deficiency and oxidation state of Co in the two materials. The oxidation state of Co is higher in La0.5Ba0.5CoO3-δ resulting in a higher electrical conductivity relative to LaBaCo2O5+δ. The conductivity in both materials was reduced with decreasing partial pressure of oxygen pointing to a p-type semiconducting behavior.
Highlights
Layered double perovskite (LDP) materials with mixed ionic-electronic conductivity and high catalytic activity have been heavily investigated because of their potential application in electrochemical devices such as solid oxide fuel cells (SOFC) [1,2,3,4,5,6,7,8] or gas separation membranes [9,10].These materials are described with a general formula LnBaM2 O5`δ where Ln is a lanthanide metal or Y and M is a transition metal
A-site cation ordered and layered double perovskite LaBaCo2 O5`δ and cubic cation disordered perovskite La0.5 Ba0.5 CoO3 ́δ were obtained from a powder synthesized by spray pyrolysis
LaBaCo2 O5`δ was prepared by thermal annealing of La0.5 Ba0.5 CoO3 ́δ in N2
Summary
Layered double perovskite (LDP) materials with mixed ionic-electronic conductivity and high catalytic activity have been heavily investigated because of their potential application in electrochemical devices such as solid oxide fuel cells (SOFC) [1,2,3,4,5,6,7,8] or gas separation membranes [9,10]. These materials are described with a general formula LnBaM2 O5`δ where Ln is a lanthanide metal or Y and M is a transition metal. A-site cation ordered GdBaMnFeO5`δ has been reported to possess superior cathode SOFC properties compared with the cubic perovskite Gd0.5 Ba0.5 Mn0.5 Fe0.5 O3 ́δ counterpart [14]
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