Effect of A-Site Cation Ordering on Chemical Stability, Oxygen Stoichiometry and Electrical Conductivity in Layered LaBaCo₂O5+δ Double Perovskite

Carlos Bernuy-Lopez; Kristin Høydalsvik; Mari-Ann Einarsrud; Tor Grande

doi:10.3390/ma9030154

Effect of A-Site Cation Ordering on Chemical Stability, Oxygen Stoichiometry and Electrical Conductivity in Layered LaBaCo₂O_5+δ Double Perovskite

Materials (Basel). 2016 Mar 3;9(3):154. doi: 10.3390/ma9030154.

Authors

Carlos Bernuy-Lopez¹, Kristin Høydalsvik², Mari-Ann Einarsrud³, Tor Grande⁴

Affiliations

¹ Department of Material Science and Engineering, NTNU Norwegian University of Science and Technology, Trondheim NO-7491, Norway. carlos.bernuy-lopez@ntnu.no.
² Department of Material Science and Engineering, NTNU Norwegian University of Science and Technology, Trondheim NO-7491, Norway. kristin.hoydalsvik@ntnu.no.
³ Department of Material Science and Engineering, NTNU Norwegian University of Science and Technology, Trondheim NO-7491, Norway. mari-ann.einarsrud@ntnu.no.
⁴ Department of Material Science and Engineering, NTNU Norwegian University of Science and Technology, Trondheim NO-7491, Norway. tor.grande@ntnu.no.

Abstract

The effect of the A-site cation ordering on the chemical stability, oxygen stoichiometry and electrical conductivity in layered LaBaCo₂O_5+δ double perovskite was studied as a function of temperature and partial pressure of oxygen. Tetragonal A-site cation ordered layered LaBaCo₂O_5+δ double perovskite was obtained by annealing cubic A-site cation disordered La_0.5Ba_0.5CoO_3-δ perovskite at 1100 °C in N₂. High temperature X-ray diffraction between room temperature (RT) and 800 °C revealed that LaBaCo₂O_5+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 LaBaCo₂O_5+δ was demonstrated. La_0.5Ba_0.5CoO_3-δ remained cubic at the studied temperature irrespective of partial pressure of oxygen. LaBaCo₂O_5+δ is metastable with respect to La_0.5Ba_0.5CoO_3-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 La_0.5Ba_0.5CoO_3-δ resulting in a higher electrical conductivity relative to LaBaCo₂O_5+δ. The conductivity in both materials was reduced with decreasing partial pressure of oxygen pointing to a p-type semiconducting behavior.

Keywords: cation and anion ordering; chemical expansion; layered double perovskite (LDP); solid oxide fuel cells.