A-site order-disorder in the NdBaMn2O5+δ SOFC electrode material monitored in situ by neutron diffraction under hydrogen flow

The A-site disordered perovskite manganite, Nd0.5Ba0.5MnO3, has been obtained by heating the A-site-ordered and vacancy ordered layered double perovskite, NdBaMn2O5, in air at 1300 degrees C for 5 h. Combined transmission electron microscopy (TEM) images and neutron powder diffraction (NPD) analysis at 25 degrees C revealed that Nd0.5Ba0.5MnO3 has a pseudotetragonal unit cell with orthorhombic symmetry (space group Imma, root 2a(p) x 2a(p) x root 2a(p)) at 20 degrees C with the cell dimensions a = 5.503(1) angstrom, b = 7.7962(4) angstrom, c = 5.502(1) angstrom, in contrast to Pm (3) over barm or Cmcm that have been previously stated from X-ray diffraction studies. The in situ neutron diffraction study carried out on Nd0.5Ba0.5MnO3 in hydrogen flow up to T similar to 900 degrees C, allows monitoring the A-site cation disorder-order structural phase transition of this representative member of potential SOFC anode materials between air sintering conditions and hydrogen working conditions. Oxygen loss from Nd0.5Ba0.5MnO3 proceeds with retention of A-site disorder until the oxygen content reaches the Nd0.5Ba0.5MnO2.5 composition at 600 degrees C. The phase transition to layered NdBaMn2O5 and localization of the oxygen vacancies in the Nd layer proceeds at 800 degrees C with retention of the oxygen content. Impedance spectroscopy measurements for the oxidized A-site ordered electrode material, NdBaMn2O6, screen printed on a Ce0.9Gd0.1O2-delta (CGO) electrolyte showed promising electrochemical performance in air at 700 degrees C with a polarization resistance of 1.09 U cm(2) without any optimization.